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ARTICLE Acute effects of pea protein and hull fibre alone and combined on blood glucose, appetite, and food intake in healthy young men – a randomized crossover trial Rebecca C. Mollard, Bohdan L. Luhovyy, Christopher Smith, and G. Harvey Anderson
Abstract: Whether pulse components can be used as value-added ingredients in foods formulated for blood glucose (BG) and food intake (FI) control requires investigation. The objective of this study was to examine of the effects of pea components on FI at an ad libitum meal, as well as appetite and BG responses before and after the meal. In a repeated-measures crossover trial, men (n = 15) randomly consumed (i) pea hull fibre (7 g), (ii) pea protein (10 g), (iii) pea protein (10 g) plus hull fibre (7 g), (iv) yellow peas (406 g), and (v) control. Pea hull fibre and protein were served with tomato sauce and noodles, while yellow peas were served with tomato sauce. Control was noodles and tomato sauce. FI was measured at a pizza meal (135 min). Appetite and BG were measured pre-pizza (0–135 min) and post-pizza (155–215 min). Protein plus fibre and yellow peas led to lower pre-pizza BG area under the curve compared with fibre and control. At 30 min, BG was lower after protein plus fibre and yellow peas compared with fibre and control, whereas at 45 and 75 min, protein plus fibre and yellow peas led to lower BG compared with fibre (p < 0.05). Following the pizza meal (155 min), yellow peas led to lower BG compared with fibre (p < 0.05). No differences were observed in FI or appetite. This trial supports the use of pea components as value-added ingredients in foods designed to improve glycemic control. Key words: pulses, fractions, glycemic control, satiety, yellow peas. Résumé : L’intégration des constituants des légumineuses dans les aliments pour en améliorer la valeur a` des fins de contrôle de la glycémie (« BG ») et de l’apport alimentaire (« FI ») requiert une expérimentation. Cette étude se propose d’examiner les effets des constituants du pois sur FI lors d’un repas ad libitum, sur l’appétit et sur la glycémie avant et après le repas. Selon un essai croisé avec mesures répétées, des hommes (n = 15) consomment aléatoirement (i) des fibres de la coque de pois (7 g), (ii) des protéines de pois (10 g), (iii) des protéines de pois (10 g) additionnées de fibres de la coque (7 g), (iv) des pois jaunes (406 g) et (v) un traitement de contrôle. On sert les fibres de la coque de pois et les protéines avec de la sauce aux tomates et des nouilles et on sert les pois jaunes avec de la sauce aux tomates. Le traitement de contrôle consiste en des nouilles et de la sauce aux tomates. On évalue FI par la consommation d’une pizza (135 min) et on évalue l’appétit et la glycémie avant (0–135 min) et après (155–215 min) la consommation de la pizza. Le traitement de protéines additionné de fibres et le traitement de pois jaunes suscitent une diminution de la surface sous la courbe de glycémie avant la consommation de la pizza comparativement aux traitements de fibres et de contrôle. À la 30e minute, la glycémie est plus faible après le traitement de protéines additionnés de fibres et le traitement de pois jaunes comparativement aux traitements de fibres et de contrôle tandis qu’a` la 45e et a` la 75e minute, le traitement de protéines additionné de fibres et le traitement de pois jaunes suscitent une plus faible glycémie comparativement au traitement de fibres (p < 0,05). Après le plat de pizza (155 min), les pois jaunes abaissent plus la glycémie comparativement au traitement de fibres (p < 0,05). On n’observe pas de différence de FI et d’appétit. Cet essai appuie l’utilisation de constituants du pois comme ingrédients a` valeur ajoutée dans les aliments conçus pour améliorer le contrôle de la glycémie. Mots-clés : légumineuses, fractions, contrôle de la glycémie, satiété, pois jaunes.
Introduction Pulses are a good source of digestible protein (McCrory et al. 2010) and contain complex carbohydrates, including soluble and insoluble fibre (Tosh and Yada 2010) as well as resistant and slowly digestible starch (Hoover et al. 2010; Tosh and Yada 2010). Many studies have identified health benefits related to pulse consumption. In epidemiologic studies, pulse consumption, alone (Papanikolaou et al. 2008) or included in a dietary pattern (Sichieri 2002; Newby et al. 2004), is associated with reduced body weight, waist circumference, and risk of overweight/obesity. In acute studies, when consumed alone, pulses have a low glycemic index (Jenkins et al. 1980; Nestel et al. 2004; Wong et al. 2009) and suppress appetite
(Wong et al. 2009) compared with white bread. When consumed within a mixed meal, pulses lower blood glucose (BG), appetite, and (or) food intake (FI) responses compared with a meal without pulses (Mollard et al. 2011, 2012). In addition, pulses reduce the postprandial BG response following a later meal (Jenkins et al. 1982; Mollard et al. 2011, 2012). Research investigating the effects of pulse components is limited. Yellow pea components are of interest because yellow peas are the least expensive and most abundant pulse, but consumption in Europe and North America is low (Schneider 2002; Mitchell et al. 2009; Mudryj et al. 2012). Safe, inexpensive and high-quality food grade pea fibre and protein fractions are available for human consumption (Smith et al. 2012). We reported previously that pea
Received 12 May 2014. Accepted 25 July 2014. R.C. Mollard, B.L. Luhovyy, C. Smith, and G.H. Anderson. Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON M5S 3E2, Canada. Corresponding author: G. Harvey Anderson (e-mail: [email protected]). Appl. Physiol. Nutr. Metab. 39: 1360–1365 (2014) dx.doi.org/10.1139/apnm-2014-0170
Published at www.nrcresearchpress.com/apnm on 2 August 2014.
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Mollard et al.
protein (10 and 20 g) led to a lower BG response from 0–30 min compared with a nonfraction low-carbohydrate soup, while 20 g of pea protein suppressed FI at 30 min and the BG response following the subsequent meal (Smith et al. 2012). However, when an ad libitum meal was consumed 120 min later, pea protein had no effect on FI or BG and appetite before or after the meal. In addition, pea hull fibre (10 and 20 g) had no effect on any study outcomes. The current trial adds to the existing literature by investigating the effects of pea protein and (or) hull fibre incorporated into a high carbohydrate treatment and compared with both a nonfraction (macaroni and tomato sauce) control and yellow peas. The objective was to examine of the effects of pea protein and hull fibre alone and in combination on FI at an ad libitum meal, as well as BG and appetite before and after the meal.
Materials and methods Participants Healthy men aged 18–35 years with a body mass index (BMI; kg/m2) of 20–24.9 were eligible and recruited through advertisements posted around the University of Toronto. The exclusion criteria were the same as previously reported (Akhavan et al. 2007; Samra et al. 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). This study took place at the University of Toronto, Department of Nutritional Sciences, from December 2007 to December 2008, and was approved by the Human Participants Review Committee, Ethics Review Office, University of Toronto. Written informed consent was obtained from participants by a research assistant. Treatments Treatments were (i) pea hull fibre (7 g), (ii) pea protein (10 g), (iii) pea hull fibre (7 g) plus pea protein (10), and (iv) yellow peas (406 g) (Table 1). Pea fibre (Centara 5, 94% fibre dry weight from hulls) and protein (Propulse, 82% protein dry weight) were commercially available and provided by Nutri-Pea Limited (Portage la Prairie, Man., Canada). The protein is isolated from the cotyledon, whereas the fibre is from the hulls and contains approximately 15% soluble and 85% insoluble fibre (Smith et al. 2012). Canned yellow peas (Nupack, Toronto, Ont., Canada) were purchased at local grocery stores. The amount of yellow peas was based upon the amount used previously (Wong et al. 2009). The amount of pea protein and hull fibre were chosen to match the quantity of protein and fibre found in the yellow pea treatment and also represent amounts that could be added to functional foods. Pea fibre and protein treatments were consumed with noodles and tomato sauce and the yellow pea was consumed with tomato sauce. Control was noodles and tomato sauce. Noodles (Kraft Canada, Inc., Don Mills, Ont., Canada) were chosen because they are a commonly consumed food and are a good source of available carbohydrate. Also, the amount of noodles varied to provide isocaloric matches among the treatments and control. The protein and protein plus fibre treatments contained 74 g of dry noodles; while the fibre and the control treatment contained 61 g. Tomato sauce was used because it is often consumed with both noodles and pulses and because the fractions were easily incorporated. Tomato sauce was prepared on premises and contained bruschetta mix (50 g, Classico, Tomato Basil, H.J. Heinz Company Canada Ltd, Toronto, Ont., Canada), diced tomatoes (75 g, Aylmer’s, Del Monte Canada, Dresden, Ont., Canada), basil (0.8 g), and garlic spice (3.1 g). Noodles were simmered in the prepared tomato sauce and water (300 mL) for 8 min. After cooking, water was added to account for differences in volume among treatments and control to ensure they were isovolumetric (575 mL) and then protein and (or) fibre were incorporated into the treatments. The yellow pea treatment was heated on high (100% power) for 2 min in a microwave oven (1200 W, Sharp Carousel R-310J, Romeoville, Ill., USA) immediately before serving. Yellow peas
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Table 1. Nutritional composition of treatments and control. Treatment
Volume Energy Protein Fibre Available Fat (mL) (kcal) (g) (g) carbohydrate (g) (g)
Control Protein Fibre Protein+fibre Yellow peas
575 575 575 575 575
324 328 322 328 322
10 18 10 18 18
2 2 10 10 10
62 55 62 55 49
4 4 4 4 6
were analyzed for nutritional composition using proximate analysis (Maxxam Analytics, Mississauga, Ont., Canada) and the nutritional composition of all other ingredients was provided by the manufacturers. A research assistant determined the order of the treatments for individual participants by a random number generator. Protocol The trial followed a single-blinded crossover design in which participants received in random order 1 of 4 treatments or control once per week (blinded to what they were receiving), 1 week apart. The protocol was similar to what has been previously described (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Smith et al. 2012). Participants chose a time between 0800 and 1100 hours to arrive for each session following an overnight fast (10–12 h). Water was permitted up until 1 h before the start of the session. Participants were instructed to refrain from alcohol consumption and unusual exercise/activity the night before a session. On arrival, participants completed questionnaires assessing their sleep habits and stress and their compliance with fasting and physical activity instructions. Those whose answers indicated feelings of illness, atypical fatigue, stress, or significant deviations from their usual patterns were asked to reschedule. Before treatment was provided, baseline BG was measured and if it was >5.5 mmol/L participants were asked to reschedule. Capillary BG was measured by the Accu-Chek monitor (Accu-Chek Compact; Roche Diagnostics Canada, Laval, Que., Canada), as previously described (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). Also, subjects completed a motivation-to-eat visual analogue scale (VAS) questionnaire to measure baseline subjective appetite (Flint et al. 2000; Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). After baseline measurements, participants were presented with 1 of the randomly assigned treatments or control and were asked to consume it within 10 min. After consumption, participants completed a VAS questionnaire assessing the palatability (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012) of the treatment or control. BG and subjective appetite were measured at 15, 30, 45, 75, and 135 min and hereafter are reported as prepizza values. At 135 min, participants were fed an ad libitum pizza meal to measure FI, as previously described (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). During the meal, participants were provided with a 300 mL bottle of water (1.5 L; Canadian Springs; Aquaterra Corp., Toronto, Ont., Canada) to measure ad libitum water intake (weight of the bottle before the meal minus the weight of the bottle after the meal). Participants were given 20 min (135–155 min) to consume the pizza meal. At the end of the test meal, participants rated the palatability of the pizza by VAS. Following the pizza meal, BG and subjective appetite were measured at 155, 170, 185, 200, and 215 min and are reported hereafter as post-pizza values. Statistical analysis Sample size was based on previous studies following a withinparticipant design that investigated the effect of protein or fibre Published by NRC Research Press
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Table 2. Food intake (FI) and water intake at the pizza meal.*
Control Fiber Protein Protein+fibre Yellow pea P
FI (kcal)
Water intake (g)
939.2±99.3 960.6±83.2 978.3±87.3 954.6±98.0 914.4±97.6 0.17
383.9±35.4 361.7±39.7 375.1±33.8 373.6±34.1 387.7±30.5 0.68
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA. *Measured at an ad libitum pizza meal consumed at 135 min.
on BG, subjective appetite, and FI (Anderson et al. 2004; Samra and Anderson 2007). Data were analyzed by SAS version 9.1 (SAS Institute, Cary, N.C., USA). Average appetite was calculated as previously described (Anderson et al. 2002). Three-way ANOVA using a PROC MIXED model was applied to test for the effects of treatment, time, and treatment-by-time interaction for pre-pizza (0– 135 min) and post-pizza (135–215 min) absolute average appetite scores and BG. Two-way repeated measures ANOVA using a PROC MIXED model was used to determine the effect of treatment at individual time points and on FI, palatability, and area under the curve (AUC) for BG and average appetite. Tukey–Kramer tests were used for all post hoc analyzes. Session (the rank order in which the treatments were given to a particular subject) was added into all analysis to account for within-participant variation. Significance was set at p < 0.05. Data are presented as means ± SE.
Results Participant characteristics Sixteen participants were recruited and completed sessions; however, 1 was removed from all analysis because he was an outlier for FI. Participants (male, n = 15) had a mean age of 21.5 ± 1.0 years, weight of 73.6 ± 1.8 kg, and BMI of 22.5 ± 0.4 kg/m2.
Table 3. Palatability of the treatments/control and pizza.
Control Fiber Protein Protein+fibre Yellow pea P
Treatments/ control* (mm)
Pizza† (mm)
56.3±5.7 46.6±6.5 48.3±6.1 41.5±5.8 41.0±6.4 0.20
73.1±3.4 73.5±3.5 68.9±3.6 73.9±1.8 70.0±2.7 0.96
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA. *Measured following the consumption of the treatments and control. †Measured following the consumption of the ad libitum pizza meal.
Table 4. Pre- and post-pizza average appetite area under the curve (AUC).* Average appetite AUC (mm/min)
Control Fiber Protein Protein+fibre Yellow pea P
Cumulative
Pre-pizza
Post-pizza
−7990.3±899.9 −8473.7±832.4 −8212.1±791.3 −8467.2±872.8 −9163.3±845.1 0.65
−3988.4±632.9 −3924.6±599.8 −4343.0±596.7 −4377.1±698.1 −4802.5±683.6 0.53
−2379.3±69.4 −3010.1±385.5 −2724.1±341.5 −2778.1±415.4 −2590.0±374.3 0.51
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA. *Cumulative: 0–215 min; pre-pizza: 0–135 min; post-pizza: 135–215 min.
Fig. 1. The effects of treatments on blood glucose (BG) at specific time points over 215 min. Treatments were control, fibre, protein, protein + fibre, and yellow peas. Different lowercase letters are significantly different at each measured time (3-way ANOVA, time-by-treatment interaction, p < 0.05, followed by 2-way ANOVA, Tukey–Kramer post hoc test, p < 0.05). All values are means ± SE (n = 15).
FI and palatability There was no effect of treatment on FI or water intake at the pizza meal (Table 2). There were no differences observed in palatability ratings among treatments and control or the pizza at the meal (Table 3). Subjective appetite Pre-pizza appetite was affected by time (p < 0.001), but there was no effect of treatment (p = 0.13) and no time-by-treatment interaction (p = 0.54). Regardless of treatment, appetite was highest when participants first arrived (75.7 ± 1.8 mm), but decreased at 15 min upon completion of the treatment or control (30.7 ± 2.2 mm), and gradually increased 57.0 ± 2.1 mm at 135 min. Pre-pizza average appetite scores were 44.4 ± 2.3, 49.4 ± 2.6, 45.1 ± 2.5, 44.5 ± 2.7, and 44.3 ± 2.9 mm for the control, fibre, protein, protein plus fibre, and yellow peas, respectively. Post-pizza appetite was affected by time (p < 0.001) but not treatment (p = 0.16) and there was no time-by-treatment interaction (p = 0.12). Immediately after the pizza meal, regardless of treatment, appetite sharply decreased to 14.0 ± 1.1 mm and gradually increased over the next hour to 24.0 ± 1.6 mm. Post-pizza average appetite scores were 24.6 ± 1.8, 26.3 ± 2.1, 26.5 ± 2.0, 26.5 ± 2.2, and 24.7 ± 2.1 mm for the control, fibre, protein, protein plus fibre, and yellow peas, respectively. There was no effect of treatment on cumulative, pre-pizza, or post-pizza appetite AUCs (Table 4). BG Pre-pizza BG was affected by time (p < 0.0001) and treatment (p < 0.0001), with a time-by-treatment interaction (p = 0.02) that was explained by the response to treatments over time (Fig. 1). At 30 min, protein plus fibre and yellow pea led to lower BG concen-
trations compared with fibre and control. At 45 and 75 min, protein plus fibre and yellow peas led to lower BG concentrations compared with fibre. Post-pizza BG was affected by time (p < 0.0001), treatment (p = 0.01), and a time-by-treatment interaction (p = 0.008) (Fig. 1). At 155 min, yellow peas led to lower post-pizza BG concentrations compared only with fibre. There was an effect of treatment on pre-pizza, but not on post-pizza BG AUC (Table 5). Protein plus fibre and yellow peas led to lower pre-pizza BG AUC compared with fibre and control, whereas the response to protein was lower compared with fibre. There was also an effect of treatment on cumulative AUC (Table 5). Protein plus fibre and yellow peas Published by NRC Research Press
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Table 5. Pre- and post-pizza blood glucose (BG) area under the curve (AUC).*
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BG AUC (mmol·min·L−1)
Control Fiber Protein Protein + fibre Yellow pea P
Cumulative
Pre-pizza
Post-pizza
284.3±22.0ab 284.2±31.1a 216.3±23.4bc 190.5±26.4c 199.1±20.2c 0.003
188.5±18.3ab 196.7±22.3a 138.1±16.8bc 124.2±16.5c 129.3±15.6c 0.003
52.7±12.5 51.3±10.6 66.5±11.4 50.8±10.7 60.7±13.3 0.87
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA, followed by Tukey–Kramer post hoc test. Values in the same column with different lowercase letters are significantly different from each other, P < 0.05. *Cumulative: 0–215 min; pre-pizza: 0–135 min; post-pizza: 135–215 min.
led to lower BG cumulative AUC compared with fibre and control, while protein led to lower values compared with fibre.
Discussion This study provides evidence that pea fractions can be used as value-added ingredients in BG control. When consumed within a treatment, containing a source of high glycemic carbohydrate, pea protein plus hull fibre reduced the glycemic response compared with the nonfraction high glycemic control; however, this was not true for either protein or fibre alone. The treatments had no effect on appetite, FI, or BG following the subsequent meal 135 min later. The mechanism(s) responsible for the beneficial effects of pea protein plus fibre on postprandial BG may be due to protein stimulation of insulin, the effects of protein and fibre on gastric emptying, and the effects of fibre on carbohydrate and protein absorption. Pea protein is readily digested, as indicated by the fact that amino acid concentrations peak approximately 30 min after consumption and return to baseline before 120 min (Calbet et al. 2002). It has been suggested that incorporating pea protein into a treatment containing available carbohydrate may increase the insulinaemic response (Smith et al. 2012), which is known to occur for other rapidly digested proteins including whey (Ma et al. 2009; Akhavan et al. 2010). In addition, as seen with whey protein (Ma et al. 2009; Akhavan et al. 2014), pea protein consumed with available carbohydrate may slow gastric emptying through the release of gut hormones. The properties of pea hull fibre that contribute to the glycemic lowering effects when consumed with protein are unclear. Dietary fibre, especially viscous fibre, slows gastric emptying, the rate of flow through the small intestine, and the rate of nutrient absorption (Jenkins et al. 1978; Ray et al. 1983; Blackburn et al. 1984; Meyer et al. 1988; Bergmann et al. 1992; Benini et al. 1995; Leterme et al. 1998; Marciani et al. 2000; Kristensen et al. 2011; Zijlstra et al. 2012; Scazzina et al. 2013). Pea hulls contain mainly cellulose (Reichert 1981), an insoluble fibre, but also contain pectins, glucans, arabinans, and hemicelluloses (Weightman et al. 1994; Renard et al. 1997). Cellulose content and the level of uronic acids (indicator of hemicelluloses) are better predictors of glycaemic response compared with soluble fibre content and insoluble fibre content has been shown to have a negative relationship with the glycaemic index (Wolever 1990). Although cellulose is known to be a nonviscous fibre, it has been shown to significantly increase viscosity and this effect can be even stronger in the presence of other types of fibre (Ang 1991). Also, water-holding capacity is closely related to viscosity. Insoluble dietary fibre has high waterholding capacity (13.4 mL/g) (Dalgetty et al. 2003; Tiwari et al. 2011), which increases in pea hulls after grinding because of the increased surface area and pore volume (Auffret et al. 1994). In a study with rats, insoluble fibre decreased free water content and increased the viscosity of digesta (Takahashi et al. 2009), which can mimic the effect of viscous fibre and affect the postprandial
glucose absorption. This is also supported by another study where pea hull fibre ingestion by healthy volunteers led to the long orocaecal transit time, which is an indicator of small intestinal transit time (Cherbut et al. 1991). Thus, the fibre(s) and mechanism(s) responsible for the effects on glycemic control when combined with protein require investigation. Future studies in which insulin, gastric emptying, and gut hormones are measured are needed to determine the mechanism(s) responsible for the combined action of pea protein and hull fibre. Pea protein alone had no effect compared with control, which may be due to both the dose of protein and the timing of the pizza meal. A previous study conducted by our laboratory showed that 10 g and 20 g pea protein consumed within a low carbohydrate soup reduced the BG response before (0–30 min) and immediately after (50–65 min) and 20 g reduced FI at an ad libitum meal 30 min later. However, similar to the findings in the current study, neither 10 nor 20 g of pea protein affected FI or BG before (0–120 min) or after (135–195 min) an ad libitum meal served 2 h later (Smith et al. 2012). Additionally in the current study, only half of the protein (10 g) came from peas and the rest was from other components (mainly noodles). This dose may have been too low to have short-term effects when given alone and added to high glycemic noodles. However, the rationale for adding the pea protein and fibre to a commonly consumed food product was to determine their benefits as value-added ingredients for improving BG and FI control and thus it was necessary that the amounts reflect those that would be added to foods. Surprisingly, the addition of pea protein did not significantly reduce the BG response at peak (30 min). Previously, it was shown that pea protein alone reduced BG over 30 min, but not over 2 h (Smith et al. 2012). In support of the present findings, an earlier study reported that although 20 g of pea protein reduced appetite 30 min following consumption and FI at meal 30 min later compared with water, it had no effect on BG before or after the meal (Abou-Samra et al. 2011). Inconsistent findings between studies may be due to the type of control and treatment used (water vs. low carbohydrate soup vs. high carbohydrate noodles) and also variations between subjects. As seen previously (Smith et al. 2012), pea hull fibre did not reduce glycemic, appetite, or FI responses compared with control. In contrast, Lunde et al. (2011) found that bread made with pea hull fibre led to lower peak BG and higher satiety ratings compared with bread without pea fibre (Lunde et al. 2011). However, their pea fibre bread not only contained more fibre (20 vs. 2.8 g) but also more protein (14.3 vs. 5.3 g) compared with their control bread. Thus, it is possible that both the higher fibre and protein content in their pea fibre bread played a role in the improved glycemic response compared with control (Lunde et al. 2011), as was seen in response to the protein plus fibre treatment in this study. Also, in the study conducted by Lunde and Colleagues, although they were matched for available carbohydrate content (25 g), the pea fibre bread was a larger portion size (119 vs. 61 g) and had higher energy content (173 vs. 135 kcal) compared with control, which likely contributed to the higher satiety ratings of the pea fibre bread (Lunde et al. 2011). In the present trial the treatments were matched for serving size and energy content. As previously speculated (Smith et al. 2012), higher doses of pea hull fibre and a longer duration of time may be needed to exert short-term benefits. The addition of 7 g of fibre in the current study and 10–20 g in a previous study (Smith et al. 2012) had no effect on study outcomes. However, higher doses (33 g) of insoluble fibre consumed within a breakfast cereal have been shown to reduce the glycemic response to a meal consumed 75 min later (Samra and Anderson 2007). In addition, indigestible carbohydrate from barley kernel (20–26 g), including fibre (11–14 g), suppresses BG, appetite, and (or) FI responses 4–16 h later (Nilsson et al. 2008a, 2008b; Johansson et al. 2013). It is also possible that the benefits observed in response to indigestible carbohydrate Published by NRC Research Press
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may be due to resistant starch, which is found in the cotyledon of yellow peas but not in the hull fibre. Despite the lower glycemic response following consumption, yellow peas had no effect on appetite, FI, or BG following the later meal compared with control. In support of these findings, yellow peas have been shown to lower glycemic response over 2 h, but have no effect on appetite or FI 2 h later compared with white bread (Wong et al. 2009). A longer duration between meals may be required to observe the benefits of yellow peas. When consumed in a standardized mixed meal, yellow peas suppressed appetite over 4 h and reduced FI 4 hours later compared with macaroni and cheese but had no effect on BG following the second meal (Mollard et al. 2011). There are limitations in the current study. First, more time (4–12 h) may be required to observe the benefits of pea hull fibre on BG, appetite, and FI control. Second, although the treatments and control were matched for energy content (isocaloric), the higher amount of available carbohydrate in the control and fibre treatment may have contributed to the higher glycemic response. Third, only pea protein and hull fibre were investigated. Fourth, although the sample size was sufficient to detect differences for blood glucose response, it may have been underpowered to detect differences between the treatments and control for appetite and food intake (Mollard et al. 2011). Finally, this study was conducted in young normal weight males and thus further research into the effects of pea fractions on BG, appetite, and FI regulation in other populations, including females and overweight/obese adults, is necessary. In conclusion, yellow pea protein and hull fibre in combination can be used as value-added ingredients in BG control and have an effect similar to canned yellow peas. Although neither protein nor fibre consumed alone resulted in a lower glycemic response compared with control, it cannot be concluded that they cannot be used as value-added ingredients on their own. Further research is needed to determine the optimal dose of pea protein and fibre for glycemic control and whether higher doses would lead to improved appetite and FI control. Also, future studies investigating the effects of other pea fractions, including starch and cotyledon fibre, are required. Finally, additional research is needed using an alternate design of later measures to determine whether pea hull fibre has beneficial effects on BG, appetite, and FI control because of fermentation of indigestible carbohydrates. Conflict of interest statement The authors have no conflicts of interest.
Acknowledgements This study was funded by Pulse Canada under the Pulse Innovation Project.
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ARTICLE Acute effects of pea protein and hull fibre alone and combined on blood glucose, appetite, and food intake in healthy young men – a randomized crossover trial Rebecca C. Mollard, Bohdan L. Luhovyy, Christopher Smith, and G. Harvey Anderson
Abstract: Whether pulse components can be used as value-added ingredients in foods formulated for blood glucose (BG) and food intake (FI) control requires investigation. The objective of this study was to examine of the effects of pea components on FI at an ad libitum meal, as well as appetite and BG responses before and after the meal. In a repeated-measures crossover trial, men (n = 15) randomly consumed (i) pea hull fibre (7 g), (ii) pea protein (10 g), (iii) pea protein (10 g) plus hull fibre (7 g), (iv) yellow peas (406 g), and (v) control. Pea hull fibre and protein were served with tomato sauce and noodles, while yellow peas were served with tomato sauce. Control was noodles and tomato sauce. FI was measured at a pizza meal (135 min). Appetite and BG were measured pre-pizza (0–135 min) and post-pizza (155–215 min). Protein plus fibre and yellow peas led to lower pre-pizza BG area under the curve compared with fibre and control. At 30 min, BG was lower after protein plus fibre and yellow peas compared with fibre and control, whereas at 45 and 75 min, protein plus fibre and yellow peas led to lower BG compared with fibre (p < 0.05). Following the pizza meal (155 min), yellow peas led to lower BG compared with fibre (p < 0.05). No differences were observed in FI or appetite. This trial supports the use of pea components as value-added ingredients in foods designed to improve glycemic control. Key words: pulses, fractions, glycemic control, satiety, yellow peas. Résumé : L’intégration des constituants des légumineuses dans les aliments pour en améliorer la valeur a` des fins de contrôle de la glycémie (« BG ») et de l’apport alimentaire (« FI ») requiert une expérimentation. Cette étude se propose d’examiner les effets des constituants du pois sur FI lors d’un repas ad libitum, sur l’appétit et sur la glycémie avant et après le repas. Selon un essai croisé avec mesures répétées, des hommes (n = 15) consomment aléatoirement (i) des fibres de la coque de pois (7 g), (ii) des protéines de pois (10 g), (iii) des protéines de pois (10 g) additionnées de fibres de la coque (7 g), (iv) des pois jaunes (406 g) et (v) un traitement de contrôle. On sert les fibres de la coque de pois et les protéines avec de la sauce aux tomates et des nouilles et on sert les pois jaunes avec de la sauce aux tomates. Le traitement de contrôle consiste en des nouilles et de la sauce aux tomates. On évalue FI par la consommation d’une pizza (135 min) et on évalue l’appétit et la glycémie avant (0–135 min) et après (155–215 min) la consommation de la pizza. Le traitement de protéines additionné de fibres et le traitement de pois jaunes suscitent une diminution de la surface sous la courbe de glycémie avant la consommation de la pizza comparativement aux traitements de fibres et de contrôle. À la 30e minute, la glycémie est plus faible après le traitement de protéines additionnés de fibres et le traitement de pois jaunes comparativement aux traitements de fibres et de contrôle tandis qu’a` la 45e et a` la 75e minute, le traitement de protéines additionné de fibres et le traitement de pois jaunes suscitent une plus faible glycémie comparativement au traitement de fibres (p < 0,05). Après le plat de pizza (155 min), les pois jaunes abaissent plus la glycémie comparativement au traitement de fibres (p < 0,05). On n’observe pas de différence de FI et d’appétit. Cet essai appuie l’utilisation de constituants du pois comme ingrédients a` valeur ajoutée dans les aliments conçus pour améliorer le contrôle de la glycémie. Mots-clés : légumineuses, fractions, contrôle de la glycémie, satiété, pois jaunes.
Introduction Pulses are a good source of digestible protein (McCrory et al. 2010) and contain complex carbohydrates, including soluble and insoluble fibre (Tosh and Yada 2010) as well as resistant and slowly digestible starch (Hoover et al. 2010; Tosh and Yada 2010). Many studies have identified health benefits related to pulse consumption. In epidemiologic studies, pulse consumption, alone (Papanikolaou et al. 2008) or included in a dietary pattern (Sichieri 2002; Newby et al. 2004), is associated with reduced body weight, waist circumference, and risk of overweight/obesity. In acute studies, when consumed alone, pulses have a low glycemic index (Jenkins et al. 1980; Nestel et al. 2004; Wong et al. 2009) and suppress appetite
(Wong et al. 2009) compared with white bread. When consumed within a mixed meal, pulses lower blood glucose (BG), appetite, and (or) food intake (FI) responses compared with a meal without pulses (Mollard et al. 2011, 2012). In addition, pulses reduce the postprandial BG response following a later meal (Jenkins et al. 1982; Mollard et al. 2011, 2012). Research investigating the effects of pulse components is limited. Yellow pea components are of interest because yellow peas are the least expensive and most abundant pulse, but consumption in Europe and North America is low (Schneider 2002; Mitchell et al. 2009; Mudryj et al. 2012). Safe, inexpensive and high-quality food grade pea fibre and protein fractions are available for human consumption (Smith et al. 2012). We reported previously that pea
Received 12 May 2014. Accepted 25 July 2014. R.C. Mollard, B.L. Luhovyy, C. Smith, and G.H. Anderson. Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON M5S 3E2, Canada. Corresponding author: G. Harvey Anderson (e-mail: [email protected]). Appl. Physiol. Nutr. Metab. 39: 1360–1365 (2014) dx.doi.org/10.1139/apnm-2014-0170
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protein (10 and 20 g) led to a lower BG response from 0–30 min compared with a nonfraction low-carbohydrate soup, while 20 g of pea protein suppressed FI at 30 min and the BG response following the subsequent meal (Smith et al. 2012). However, when an ad libitum meal was consumed 120 min later, pea protein had no effect on FI or BG and appetite before or after the meal. In addition, pea hull fibre (10 and 20 g) had no effect on any study outcomes. The current trial adds to the existing literature by investigating the effects of pea protein and (or) hull fibre incorporated into a high carbohydrate treatment and compared with both a nonfraction (macaroni and tomato sauce) control and yellow peas. The objective was to examine of the effects of pea protein and hull fibre alone and in combination on FI at an ad libitum meal, as well as BG and appetite before and after the meal.
Materials and methods Participants Healthy men aged 18–35 years with a body mass index (BMI; kg/m2) of 20–24.9 were eligible and recruited through advertisements posted around the University of Toronto. The exclusion criteria were the same as previously reported (Akhavan et al. 2007; Samra et al. 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). This study took place at the University of Toronto, Department of Nutritional Sciences, from December 2007 to December 2008, and was approved by the Human Participants Review Committee, Ethics Review Office, University of Toronto. Written informed consent was obtained from participants by a research assistant. Treatments Treatments were (i) pea hull fibre (7 g), (ii) pea protein (10 g), (iii) pea hull fibre (7 g) plus pea protein (10), and (iv) yellow peas (406 g) (Table 1). Pea fibre (Centara 5, 94% fibre dry weight from hulls) and protein (Propulse, 82% protein dry weight) were commercially available and provided by Nutri-Pea Limited (Portage la Prairie, Man., Canada). The protein is isolated from the cotyledon, whereas the fibre is from the hulls and contains approximately 15% soluble and 85% insoluble fibre (Smith et al. 2012). Canned yellow peas (Nupack, Toronto, Ont., Canada) were purchased at local grocery stores. The amount of yellow peas was based upon the amount used previously (Wong et al. 2009). The amount of pea protein and hull fibre were chosen to match the quantity of protein and fibre found in the yellow pea treatment and also represent amounts that could be added to functional foods. Pea fibre and protein treatments were consumed with noodles and tomato sauce and the yellow pea was consumed with tomato sauce. Control was noodles and tomato sauce. Noodles (Kraft Canada, Inc., Don Mills, Ont., Canada) were chosen because they are a commonly consumed food and are a good source of available carbohydrate. Also, the amount of noodles varied to provide isocaloric matches among the treatments and control. The protein and protein plus fibre treatments contained 74 g of dry noodles; while the fibre and the control treatment contained 61 g. Tomato sauce was used because it is often consumed with both noodles and pulses and because the fractions were easily incorporated. Tomato sauce was prepared on premises and contained bruschetta mix (50 g, Classico, Tomato Basil, H.J. Heinz Company Canada Ltd, Toronto, Ont., Canada), diced tomatoes (75 g, Aylmer’s, Del Monte Canada, Dresden, Ont., Canada), basil (0.8 g), and garlic spice (3.1 g). Noodles were simmered in the prepared tomato sauce and water (300 mL) for 8 min. After cooking, water was added to account for differences in volume among treatments and control to ensure they were isovolumetric (575 mL) and then protein and (or) fibre were incorporated into the treatments. The yellow pea treatment was heated on high (100% power) for 2 min in a microwave oven (1200 W, Sharp Carousel R-310J, Romeoville, Ill., USA) immediately before serving. Yellow peas
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Table 1. Nutritional composition of treatments and control. Treatment
Volume Energy Protein Fibre Available Fat (mL) (kcal) (g) (g) carbohydrate (g) (g)
Control Protein Fibre Protein+fibre Yellow peas
575 575 575 575 575
324 328 322 328 322
10 18 10 18 18
2 2 10 10 10
62 55 62 55 49
4 4 4 4 6
were analyzed for nutritional composition using proximate analysis (Maxxam Analytics, Mississauga, Ont., Canada) and the nutritional composition of all other ingredients was provided by the manufacturers. A research assistant determined the order of the treatments for individual participants by a random number generator. Protocol The trial followed a single-blinded crossover design in which participants received in random order 1 of 4 treatments or control once per week (blinded to what they were receiving), 1 week apart. The protocol was similar to what has been previously described (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Smith et al. 2012). Participants chose a time between 0800 and 1100 hours to arrive for each session following an overnight fast (10–12 h). Water was permitted up until 1 h before the start of the session. Participants were instructed to refrain from alcohol consumption and unusual exercise/activity the night before a session. On arrival, participants completed questionnaires assessing their sleep habits and stress and their compliance with fasting and physical activity instructions. Those whose answers indicated feelings of illness, atypical fatigue, stress, or significant deviations from their usual patterns were asked to reschedule. Before treatment was provided, baseline BG was measured and if it was >5.5 mmol/L participants were asked to reschedule. Capillary BG was measured by the Accu-Chek monitor (Accu-Chek Compact; Roche Diagnostics Canada, Laval, Que., Canada), as previously described (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). Also, subjects completed a motivation-to-eat visual analogue scale (VAS) questionnaire to measure baseline subjective appetite (Flint et al. 2000; Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). After baseline measurements, participants were presented with 1 of the randomly assigned treatments or control and were asked to consume it within 10 min. After consumption, participants completed a VAS questionnaire assessing the palatability (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012) of the treatment or control. BG and subjective appetite were measured at 15, 30, 45, 75, and 135 min and hereafter are reported as prepizza values. At 135 min, participants were fed an ad libitum pizza meal to measure FI, as previously described (Akhavan and Anderson 2007; Samra and Anderson 2007; Wong et al. 2009; Mollard et al. 2011, 2012; Smith et al. 2012). During the meal, participants were provided with a 300 mL bottle of water (1.5 L; Canadian Springs; Aquaterra Corp., Toronto, Ont., Canada) to measure ad libitum water intake (weight of the bottle before the meal minus the weight of the bottle after the meal). Participants were given 20 min (135–155 min) to consume the pizza meal. At the end of the test meal, participants rated the palatability of the pizza by VAS. Following the pizza meal, BG and subjective appetite were measured at 155, 170, 185, 200, and 215 min and are reported hereafter as post-pizza values. Statistical analysis Sample size was based on previous studies following a withinparticipant design that investigated the effect of protein or fibre Published by NRC Research Press
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Table 2. Food intake (FI) and water intake at the pizza meal.*
Control Fiber Protein Protein+fibre Yellow pea P
FI (kcal)
Water intake (g)
939.2±99.3 960.6±83.2 978.3±87.3 954.6±98.0 914.4±97.6 0.17
383.9±35.4 361.7±39.7 375.1±33.8 373.6±34.1 387.7±30.5 0.68
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA. *Measured at an ad libitum pizza meal consumed at 135 min.
on BG, subjective appetite, and FI (Anderson et al. 2004; Samra and Anderson 2007). Data were analyzed by SAS version 9.1 (SAS Institute, Cary, N.C., USA). Average appetite was calculated as previously described (Anderson et al. 2002). Three-way ANOVA using a PROC MIXED model was applied to test for the effects of treatment, time, and treatment-by-time interaction for pre-pizza (0– 135 min) and post-pizza (135–215 min) absolute average appetite scores and BG. Two-way repeated measures ANOVA using a PROC MIXED model was used to determine the effect of treatment at individual time points and on FI, palatability, and area under the curve (AUC) for BG and average appetite. Tukey–Kramer tests were used for all post hoc analyzes. Session (the rank order in which the treatments were given to a particular subject) was added into all analysis to account for within-participant variation. Significance was set at p < 0.05. Data are presented as means ± SE.
Results Participant characteristics Sixteen participants were recruited and completed sessions; however, 1 was removed from all analysis because he was an outlier for FI. Participants (male, n = 15) had a mean age of 21.5 ± 1.0 years, weight of 73.6 ± 1.8 kg, and BMI of 22.5 ± 0.4 kg/m2.
Table 3. Palatability of the treatments/control and pizza.
Control Fiber Protein Protein+fibre Yellow pea P
Treatments/ control* (mm)
Pizza† (mm)
56.3±5.7 46.6±6.5 48.3±6.1 41.5±5.8 41.0±6.4 0.20
73.1±3.4 73.5±3.5 68.9±3.6 73.9±1.8 70.0±2.7 0.96
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA. *Measured following the consumption of the treatments and control. †Measured following the consumption of the ad libitum pizza meal.
Table 4. Pre- and post-pizza average appetite area under the curve (AUC).* Average appetite AUC (mm/min)
Control Fiber Protein Protein+fibre Yellow pea P
Cumulative
Pre-pizza
Post-pizza
−7990.3±899.9 −8473.7±832.4 −8212.1±791.3 −8467.2±872.8 −9163.3±845.1 0.65
−3988.4±632.9 −3924.6±599.8 −4343.0±596.7 −4377.1±698.1 −4802.5±683.6 0.53
−2379.3±69.4 −3010.1±385.5 −2724.1±341.5 −2778.1±415.4 −2590.0±374.3 0.51
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA. *Cumulative: 0–215 min; pre-pizza: 0–135 min; post-pizza: 135–215 min.
Fig. 1. The effects of treatments on blood glucose (BG) at specific time points over 215 min. Treatments were control, fibre, protein, protein + fibre, and yellow peas. Different lowercase letters are significantly different at each measured time (3-way ANOVA, time-by-treatment interaction, p < 0.05, followed by 2-way ANOVA, Tukey–Kramer post hoc test, p < 0.05). All values are means ± SE (n = 15).
FI and palatability There was no effect of treatment on FI or water intake at the pizza meal (Table 2). There were no differences observed in palatability ratings among treatments and control or the pizza at the meal (Table 3). Subjective appetite Pre-pizza appetite was affected by time (p < 0.001), but there was no effect of treatment (p = 0.13) and no time-by-treatment interaction (p = 0.54). Regardless of treatment, appetite was highest when participants first arrived (75.7 ± 1.8 mm), but decreased at 15 min upon completion of the treatment or control (30.7 ± 2.2 mm), and gradually increased 57.0 ± 2.1 mm at 135 min. Pre-pizza average appetite scores were 44.4 ± 2.3, 49.4 ± 2.6, 45.1 ± 2.5, 44.5 ± 2.7, and 44.3 ± 2.9 mm for the control, fibre, protein, protein plus fibre, and yellow peas, respectively. Post-pizza appetite was affected by time (p < 0.001) but not treatment (p = 0.16) and there was no time-by-treatment interaction (p = 0.12). Immediately after the pizza meal, regardless of treatment, appetite sharply decreased to 14.0 ± 1.1 mm and gradually increased over the next hour to 24.0 ± 1.6 mm. Post-pizza average appetite scores were 24.6 ± 1.8, 26.3 ± 2.1, 26.5 ± 2.0, 26.5 ± 2.2, and 24.7 ± 2.1 mm for the control, fibre, protein, protein plus fibre, and yellow peas, respectively. There was no effect of treatment on cumulative, pre-pizza, or post-pizza appetite AUCs (Table 4). BG Pre-pizza BG was affected by time (p < 0.0001) and treatment (p < 0.0001), with a time-by-treatment interaction (p = 0.02) that was explained by the response to treatments over time (Fig. 1). At 30 min, protein plus fibre and yellow pea led to lower BG concen-
trations compared with fibre and control. At 45 and 75 min, protein plus fibre and yellow peas led to lower BG concentrations compared with fibre. Post-pizza BG was affected by time (p < 0.0001), treatment (p = 0.01), and a time-by-treatment interaction (p = 0.008) (Fig. 1). At 155 min, yellow peas led to lower post-pizza BG concentrations compared only with fibre. There was an effect of treatment on pre-pizza, but not on post-pizza BG AUC (Table 5). Protein plus fibre and yellow peas led to lower pre-pizza BG AUC compared with fibre and control, whereas the response to protein was lower compared with fibre. There was also an effect of treatment on cumulative AUC (Table 5). Protein plus fibre and yellow peas Published by NRC Research Press
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Table 5. Pre- and post-pizza blood glucose (BG) area under the curve (AUC).*
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BG AUC (mmol·min·L−1)
Control Fiber Protein Protein + fibre Yellow pea P
Cumulative
Pre-pizza
Post-pizza
284.3±22.0ab 284.2±31.1a 216.3±23.4bc 190.5±26.4c 199.1±20.2c 0.003
188.5±18.3ab 196.7±22.3a 138.1±16.8bc 124.2±16.5c 129.3±15.6c 0.003
52.7±12.5 51.3±10.6 66.5±11.4 50.8±10.7 60.7±13.3 0.87
Note: All values are means ± SE (n = 15). Two-way (treatment, session) ANOVA, followed by Tukey–Kramer post hoc test. Values in the same column with different lowercase letters are significantly different from each other, P < 0.05. *Cumulative: 0–215 min; pre-pizza: 0–135 min; post-pizza: 135–215 min.
led to lower BG cumulative AUC compared with fibre and control, while protein led to lower values compared with fibre.
Discussion This study provides evidence that pea fractions can be used as value-added ingredients in BG control. When consumed within a treatment, containing a source of high glycemic carbohydrate, pea protein plus hull fibre reduced the glycemic response compared with the nonfraction high glycemic control; however, this was not true for either protein or fibre alone. The treatments had no effect on appetite, FI, or BG following the subsequent meal 135 min later. The mechanism(s) responsible for the beneficial effects of pea protein plus fibre on postprandial BG may be due to protein stimulation of insulin, the effects of protein and fibre on gastric emptying, and the effects of fibre on carbohydrate and protein absorption. Pea protein is readily digested, as indicated by the fact that amino acid concentrations peak approximately 30 min after consumption and return to baseline before 120 min (Calbet et al. 2002). It has been suggested that incorporating pea protein into a treatment containing available carbohydrate may increase the insulinaemic response (Smith et al. 2012), which is known to occur for other rapidly digested proteins including whey (Ma et al. 2009; Akhavan et al. 2010). In addition, as seen with whey protein (Ma et al. 2009; Akhavan et al. 2014), pea protein consumed with available carbohydrate may slow gastric emptying through the release of gut hormones. The properties of pea hull fibre that contribute to the glycemic lowering effects when consumed with protein are unclear. Dietary fibre, especially viscous fibre, slows gastric emptying, the rate of flow through the small intestine, and the rate of nutrient absorption (Jenkins et al. 1978; Ray et al. 1983; Blackburn et al. 1984; Meyer et al. 1988; Bergmann et al. 1992; Benini et al. 1995; Leterme et al. 1998; Marciani et al. 2000; Kristensen et al. 2011; Zijlstra et al. 2012; Scazzina et al. 2013). Pea hulls contain mainly cellulose (Reichert 1981), an insoluble fibre, but also contain pectins, glucans, arabinans, and hemicelluloses (Weightman et al. 1994; Renard et al. 1997). Cellulose content and the level of uronic acids (indicator of hemicelluloses) are better predictors of glycaemic response compared with soluble fibre content and insoluble fibre content has been shown to have a negative relationship with the glycaemic index (Wolever 1990). Although cellulose is known to be a nonviscous fibre, it has been shown to significantly increase viscosity and this effect can be even stronger in the presence of other types of fibre (Ang 1991). Also, water-holding capacity is closely related to viscosity. Insoluble dietary fibre has high waterholding capacity (13.4 mL/g) (Dalgetty et al. 2003; Tiwari et al. 2011), which increases in pea hulls after grinding because of the increased surface area and pore volume (Auffret et al. 1994). In a study with rats, insoluble fibre decreased free water content and increased the viscosity of digesta (Takahashi et al. 2009), which can mimic the effect of viscous fibre and affect the postprandial
glucose absorption. This is also supported by another study where pea hull fibre ingestion by healthy volunteers led to the long orocaecal transit time, which is an indicator of small intestinal transit time (Cherbut et al. 1991). Thus, the fibre(s) and mechanism(s) responsible for the effects on glycemic control when combined with protein require investigation. Future studies in which insulin, gastric emptying, and gut hormones are measured are needed to determine the mechanism(s) responsible for the combined action of pea protein and hull fibre. Pea protein alone had no effect compared with control, which may be due to both the dose of protein and the timing of the pizza meal. A previous study conducted by our laboratory showed that 10 g and 20 g pea protein consumed within a low carbohydrate soup reduced the BG response before (0–30 min) and immediately after (50–65 min) and 20 g reduced FI at an ad libitum meal 30 min later. However, similar to the findings in the current study, neither 10 nor 20 g of pea protein affected FI or BG before (0–120 min) or after (135–195 min) an ad libitum meal served 2 h later (Smith et al. 2012). Additionally in the current study, only half of the protein (10 g) came from peas and the rest was from other components (mainly noodles). This dose may have been too low to have short-term effects when given alone and added to high glycemic noodles. However, the rationale for adding the pea protein and fibre to a commonly consumed food product was to determine their benefits as value-added ingredients for improving BG and FI control and thus it was necessary that the amounts reflect those that would be added to foods. Surprisingly, the addition of pea protein did not significantly reduce the BG response at peak (30 min). Previously, it was shown that pea protein alone reduced BG over 30 min, but not over 2 h (Smith et al. 2012). In support of the present findings, an earlier study reported that although 20 g of pea protein reduced appetite 30 min following consumption and FI at meal 30 min later compared with water, it had no effect on BG before or after the meal (Abou-Samra et al. 2011). Inconsistent findings between studies may be due to the type of control and treatment used (water vs. low carbohydrate soup vs. high carbohydrate noodles) and also variations between subjects. As seen previously (Smith et al. 2012), pea hull fibre did not reduce glycemic, appetite, or FI responses compared with control. In contrast, Lunde et al. (2011) found that bread made with pea hull fibre led to lower peak BG and higher satiety ratings compared with bread without pea fibre (Lunde et al. 2011). However, their pea fibre bread not only contained more fibre (20 vs. 2.8 g) but also more protein (14.3 vs. 5.3 g) compared with their control bread. Thus, it is possible that both the higher fibre and protein content in their pea fibre bread played a role in the improved glycemic response compared with control (Lunde et al. 2011), as was seen in response to the protein plus fibre treatment in this study. Also, in the study conducted by Lunde and Colleagues, although they were matched for available carbohydrate content (25 g), the pea fibre bread was a larger portion size (119 vs. 61 g) and had higher energy content (173 vs. 135 kcal) compared with control, which likely contributed to the higher satiety ratings of the pea fibre bread (Lunde et al. 2011). In the present trial the treatments were matched for serving size and energy content. As previously speculated (Smith et al. 2012), higher doses of pea hull fibre and a longer duration of time may be needed to exert short-term benefits. The addition of 7 g of fibre in the current study and 10–20 g in a previous study (Smith et al. 2012) had no effect on study outcomes. However, higher doses (33 g) of insoluble fibre consumed within a breakfast cereal have been shown to reduce the glycemic response to a meal consumed 75 min later (Samra and Anderson 2007). In addition, indigestible carbohydrate from barley kernel (20–26 g), including fibre (11–14 g), suppresses BG, appetite, and (or) FI responses 4–16 h later (Nilsson et al. 2008a, 2008b; Johansson et al. 2013). It is also possible that the benefits observed in response to indigestible carbohydrate Published by NRC Research Press
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may be due to resistant starch, which is found in the cotyledon of yellow peas but not in the hull fibre. Despite the lower glycemic response following consumption, yellow peas had no effect on appetite, FI, or BG following the later meal compared with control. In support of these findings, yellow peas have been shown to lower glycemic response over 2 h, but have no effect on appetite or FI 2 h later compared with white bread (Wong et al. 2009). A longer duration between meals may be required to observe the benefits of yellow peas. When consumed in a standardized mixed meal, yellow peas suppressed appetite over 4 h and reduced FI 4 hours later compared with macaroni and cheese but had no effect on BG following the second meal (Mollard et al. 2011). There are limitations in the current study. First, more time (4–12 h) may be required to observe the benefits of pea hull fibre on BG, appetite, and FI control. Second, although the treatments and control were matched for energy content (isocaloric), the higher amount of available carbohydrate in the control and fibre treatment may have contributed to the higher glycemic response. Third, only pea protein and hull fibre were investigated. Fourth, although the sample size was sufficient to detect differences for blood glucose response, it may have been underpowered to detect differences between the treatments and control for appetite and food intake (Mollard et al. 2011). Finally, this study was conducted in young normal weight males and thus further research into the effects of pea fractions on BG, appetite, and FI regulation in other populations, including females and overweight/obese adults, is necessary. In conclusion, yellow pea protein and hull fibre in combination can be used as value-added ingredients in BG control and have an effect similar to canned yellow peas. Although neither protein nor fibre consumed alone resulted in a lower glycemic response compared with control, it cannot be concluded that they cannot be used as value-added ingredients on their own. Further research is needed to determine the optimal dose of pea protein and fibre for glycemic control and whether higher doses would lead to improved appetite and FI control. Also, future studies investigating the effects of other pea fractions, including starch and cotyledon fibre, are required. Finally, additional research is needed using an alternate design of later measures to determine whether pea hull fibre has beneficial effects on BG, appetite, and FI control because of fermentation of indigestible carbohydrates. Conflict of interest statement The authors have no conflicts of interest.
Acknowledgements This study was funded by Pulse Canada under the Pulse Innovation Project.
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