9 1985 by The Humana Press Inc. All rights of any nature whatsoever reserved. 0163-4984/85/0809~093502.40
Effect of a Moderate Variation in Dietary Energy Intake on the Retention and Excretion of Zinc, Calcium, and Magnesium T. ATINMO,~ I. O. ADEYEFA, E. A. FADERO, AND J. F, OLORUNLEKE
Department of Human Nutrition, College of Aledicine, University of lbadan, lbadan, Nigeria Received January 4, 1985; Accepted February 26, 1985 ABSTRACT Mineral balance was studied by metabolic balance techniques in 13 healthy college females aged 21-23 yr. They were fed diet containing 1780 kcal, 2580 kcal, and 25 g protein in a 20-d experiment period. Both diets contained approximately 5.28 mg zinc, 216.85 mg calcium, and 364.3 mg magnesium. The diet consisted of habitually consumed foods. Blood, urine and fecal samples were collected for mineral analysis using atomic absorption spectrophotometry. Plasma mineral levels were not affected by the change in dietary energy intake. Fecal calcium and magnesium were significantly higher when subjects were fed the low calorie (1780 kcal) diet, whereas there was no significant difference in fecal zinc for the two levels of dietary energy. Urinary calcium and magnesium were also significantly higher w h e n the diet provided 1780 kcal though, on the other hand, urinary zinc was significantly higher when the diet provided 2680 kcal (P 0.05). Urinary calcium and magnesium correlated negatively, whereas urinary zinc correlated positively, with the dietary energy intake (P~ ( 0 . 0 5 ) . Dietary energy intake has a significant effect on the mineral balance of the subjects.
*Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
93
Vol. 8, 1985
94
A t i n m o et aL
Index Entries: Dietary energy intake, and Zn, Ca, and Mg balance; mineral balance, and dietary intake; calcium, dietary intake and balance; magnesium, dietary intake and balance; zinc, dietary intake and balance.
INTRODUCTION Increasing attention is being focused on the effect of dietary components on the absorption and utilization of essential minerals. The effect of dietary protein on zinc, calcium, and magnesium has been extensively studied (1-3). On the other hand, very little work has been d o n e in the direction of relating calorie intake to mineral balance. Mahalko et al. (3) found that there was a statistically significant increase in urinary calcium from a relatively modest increase in dietary protein. Walker and Linkswiller (4) found that increased protein intake caused an increase in urinary calcium, thereby resulting in impaired calcium balance. Total calorie intake has also been found to affect calcium balance. In their various studies, Brown et al. (5), Leverton et al. (6), Young (7), and Young et al. (8), found that young w o m e n fed weightreducing diets exhibited a reduced calcium retention and in most cases a negative calcium balance. Decreased calcium absorption (5) and increased calcium excretion (7) were observed during the periods of low calorie intake, or possibly the decreased proportion of protein in the diet, was not clear. The effect of dietary protein on magnesium balance has also been demonstrated. Schwartz et al. (8) demonstrated that high protein intake in the presence of adequate magnesium intake led to negative magnesium balance in nonpregnant women; but the level of energy intake in the study was not indicated. Romualda et al. (10) in their studies related calorie content of diet to their m a g n e s i u m content. They concluded that a diet supplying an average of 3000 kcal d would contain about 342 m g of magnesium, but they failed to highlight what the m a g n e s i u m status of the subjects is likely to be. Jourdan (11) concluded that-both urinary calcium and magnesium excretions were depressed with calcium intake. The zinc content of a diet has also been related to the protein content (12). Greger and Snedeker (1) observed a significant increase in both fecal and urinary zinc excretions w h e n subjects were fed high protein diets. Dietary protein has also been found to affect the absorption of zinc. Greger and Snedeker (1) and Van Campen and House (13) observed a significant increase in apparent absorption of zinc w h e n subjects were fed high levels of dietary intake. However, Price et al. (14), Meiners et al. (15), and Colin et al. (16), working with h u m a n subjects, found that variation in dietary protein levels did not consistently affect apparent absorption and retention of zinc.
Biological Trace Elernent Research
VoL 8, 1985
Energy Intake and ~lineral Balance
95
Although very little work has been carried out to relate calorie intake directly with zinc balance, Spencer and Samachsen (17) observed that urinary zinc excretion rose to high levels during total starvation (no calories). In view of the findings above, this study was designed to investigate the direct effect of a moderate change in calorie intake on zinc, calcium and magnesium balance in young women fed on a habitually consumed diet.
MATERIALS AND METHODS Subjects and ExpeHrnental Design Thirteen female students of the University of Ibadan volunteered to participate in the study. The subjects had no known metabolic disorders. Their mean body weight was 53 kg. Subjects were not confined within the laboratory during the study. However, they were required to consume all their meals at the metabolic facility during supervised time periods, to weigh themselves before breakfast under standardized condit-ion (post voiding and minimal clothing) using Salter Scale and to collect all fecal and urine samples in designated containers. Blood samples were taken at the beginning and end of each experimental diet period. All the subjects were students, and they continued to attend classes regularly. They limited their participation in rigorous activities during the study. The balance study consisted of two experimental diet periods each of 10 d duration. Two different levels of energy (low and high) were fed, while protein intake was adequate based on a previously determined minimum nitrogen requirement (2). The low and high energy diets contained 1780 and 2580 kcal/d, respectively, and the adequate protein intake 25 g/d (0.47 g/kg body wt). All subjects were on the low energy diet during the first experimental period after a 3-d break, they were placed on the high energy diet. The subjects received a protein-free diet on the first day of each experimental diet period.
DIET Diets were standardized based on food habitually consumed and meal patterns the subjects were accustomed to. The basal diet fed throughout the study contained 90 g bread, tea, 15 g sugar as breakfast, 300 g grated cassava (eba), 60 g stew, 15 g vegetable, and 20 g meat as lunch; and 300 g rice 60 g stew, and 20 g meat as dinner. The diet for the low energy intake was supplemented with one bottle of carbonated drink whereas that of high energy was supplemented with two bottles of carbonated drink, 30 g margarine, 15 g sugar, and 100 g caloreen (Table 1).
Biological Trace Element Research
VoL 8, I g85
96
A t i n m o et aL
TABLE 1 Experimental Diet--High and Low Energy Intake Average body weight Protein intake High energy intake Low energy intake
Breakfast Bread Tea Sugar Margarine Lunch
Stew Vegetable Meat
Amount, g
53 kg = 0.47 g/protein/kg body wt (or 25 g/protein/d) = 2556.72 kcal = 1704.48 kcal =
Protein, g
90
High energy, kcal 209.7 120 219 263.25 300 2.9 53.33 420 300 53.33 400 240 2581.51
15 (30)~ 30 300 60 15 20
--0.75 0.88 0.5 4.0
209.7 . 60 -263.25 300 2.9 53.33
300 60 20 100b 1 Bottle
6.9 0.88 4.0 --24.93
420 300 53~ -120 1782.51
.
7.02
Low energy, kcal
.
.
Dinner
Rice Stew Meat Caloreen Soft drinks Total:
"High energy intake. bGlucose polymer.
ANALYSES Food, fecal, and urine samples were collected and stored in labeled plastic containers. Blood samples were collected into heparinized bottles. Containers for samples had been previously w a s h e d with d e t e r g e n t (Teepol), soaked in 1N HC1 overnight to remove soap residue, a n d t h e n rinsed thoroughly in deionized water. Fecal marker (camine) was administered to subjects after dinner on days 6 and 11 of each experimental period to mark the beginning and e n d of the collection period. Feces w e r e composited accordingly, w h e r e a s urine samples were composited daily. Food samples were collected daily from days 6 to 10 of each e x p e r i m e n t a l period. The 5 g fecal samples were pre-ashed. The ashed samples w e r e diluted in 50 mL volumetric flasks with 10 mL of 3N HC1 a n d m a d e to v o l u m e with deionized water. Aliquots were then taken a n d areas read on Perkin Elmer Atomic Absorption Spectrophotometer (AAS) Model Biological Trace Element Research
Vol. 8, 1985
Energy Intake and Mineral Balance
97
4000. Food samples were digested using 25 mL of 69% HC1. The samples were then heated for 5 rain and allowed to simmer for another 5 min. The samples were then filtered into sample bottles using W a t e r m a n Filter Paper No. 1. Samples were then read on the AAS for zinc. For calcium and magnesium, 5 mL samples were taken, 2 mL 1% l a n t h a n u m chloride solution was a d d e d in 100 mL volumetric flasks, and then m a d e to volume. Readings w e r e taken using AAS. Urine samples were diluted in the proportion of I part of urine plus 4 parts of deionized water, and into 0.1 mL of urine, 20 mL deionized water was added, and read on AAS for zinc and m a g n e s i u m , respectively; 2 mL of urine was made up to 10 mL with l a n t h a n u m chloride solution and the calcium concentrations w e r e then read on the AAS. Serum samples were also diluted in the proportion of 1:4 for zinc, 1:50 for m a g n e s i u m , and 0.25 of serum to 4 mL of deionized water p l u s 0.5 mL of l a n t h a n u m chloride and m a d e up to 5 mL with deionized water for calcium. The samples were read on the AAS~
RESULTS There was a reduction of 1.4 kg in the m e a n body weights of subjects during the low energy phase, whereas an increase of 0.6 kg was observed during the high energy diet. The diets were analyzed and found to contain 5.28 mg zinc, 216.8 m g calcium, and 364.3 m g magnesium. Fecal zinc was higher than the level of dietary zinc fed to subjects in the study. M e a n fecal zinc (mg) was higher during the high e n e r g y diet (7.2 • 2.9 vs 5.8 m 2.6). A positive correlation (r = 0.2) was observed b e t w e e n the dietary intake of energy and fecal zinc. However, the effect was not statistically significant (P ( 0 . 0 5 ) . Fecal calcium was significantly lower (P ( 0 . 0 5 ) during the high energy phase. A nonsignificant negative correlation (r = -0.12) was observed bet w e e n energy intake and fecal magnesium. There was a steady reduction in the urinary zinc output during the low energy phase. The level of urinary zinc fell from 0.5 mg/d on d 1 to 0.3 mg/d on d 10. On the other hand, a persistent rise was observed during the high energy diet. The level rose from 1.8 mg on d 1 to 2.5 mg/d on d 10. Dietary energy had a significant (P ( 0 . 0 5 ) effect on urinary zinc losses of the subjects. Dietary energy also had a significant effect on urinary calcium. Urinary calcium losses were significantly (P < 0.05) higher during the low energy phase. M a g n e s i u m excretion in urine was also significantly higher during the low energy intake (P ( 0 . 0 5 ) . Table 2 shows the regression equation of the dietary energy and urinary losses of the minerals. It can be observed from the table that urinary Biological Trace Element Research
Voi. 8, t 985
98
A t i n m o et aL
TABLE 2 Simple Regression and Correlation Between Dietary Energy Intake and Urinary Zn, Ca, and Mg Minerals
Regression equation ~
r
pb
Zinc Calcium Magnesium
Y = 0 . 0 9 X - 2.7 Y = 0.921X + 118.73 Y = 55.6 - 0.20X
0.92 -0.77 -0.93
0.05 0.05 0.05
"Y = level of dietary e n e r g y intake, bp = level of significance of the correlation coefficient (r).
zinc is positively correlated to dietary energy intake, whereas urinary caicium a n d m a g n e s i u m are negatively correlated to dietary e n e r g y intake. Six subjects were in positive zinc retention during the low e n e r g y diet w h e r e a s only one subject was in positive zinc retention during the high e n e r g y diet. Mean apparent retentions were negative for both levels of dietary energy intake (-0.91 and -4.08 mg/d for the low and high energy diets, respectively) (Table 3). More zinc was retained during the low e n e r g y diet. Dietary energy intake had a significant effect on the apparent retention of zinc in the subjects (r = 0.408, P < 0.05). All subjects were in negative Ca retention during the two levels of dietary energy intake. A p p a r e n t calcium retention was significantly d e p e n d e n t on the energy intake (r = 0.35, P < 0.05). A p p a r e n t m a g n e s i u m retention was significantly lower (P < 0.05) d u r i n g the low energy diet compared to the high energy phase. Eight subjects were in negative balance during the low energy phase, w h e r e a s all subjects were in positive balance during the high energy phase. Dietary e n e r g y was significantly correlated (r = 0.90, P < 0.05) with magnesium retention. There was no significant difference between the serum zinc levels for the two energy phases and also w h e n values were compared with the value at the beginning of the study. Moderate increase in dietary e n e r g y intake had no effect on serum zinc levels. A slightly higher increase (0.2 rag%) was observed in s e r u m calcium d u r i n g the high energy diet, but the effect was not significant. Serum m a g n e s i u m was equally not affected by the level of dietary e n e r g y intake, though a slight decrease in serum m a g n e s i u m was observed at the end of the high energy diet.
DISCUSSION The loss of weight observed in the subjects was a result of the reduction in the energy intake of the subjects. To meet the energy n e e d of tissues, it is possible that b r e a k d o w n of muscle protein occurred, leading to s u b s e q u e n t loss of weight and a reduction in the mid-arm circumference, Biological Trace Element Research
Vol. 8, ]985
Energy Intake and ~ineral Balance
99
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Effect of a Moderate Variation in Dietary Energy Intake on the Retention and Excretion of Zinc, Calcium, and Magnesium T. ATINMO,~ I. O. ADEYEFA, E. A. FADERO, AND J. F, OLORUNLEKE
Department of Human Nutrition, College of Aledicine, University of lbadan, lbadan, Nigeria Received January 4, 1985; Accepted February 26, 1985 ABSTRACT Mineral balance was studied by metabolic balance techniques in 13 healthy college females aged 21-23 yr. They were fed diet containing 1780 kcal, 2580 kcal, and 25 g protein in a 20-d experiment period. Both diets contained approximately 5.28 mg zinc, 216.85 mg calcium, and 364.3 mg magnesium. The diet consisted of habitually consumed foods. Blood, urine and fecal samples were collected for mineral analysis using atomic absorption spectrophotometry. Plasma mineral levels were not affected by the change in dietary energy intake. Fecal calcium and magnesium were significantly higher when subjects were fed the low calorie (1780 kcal) diet, whereas there was no significant difference in fecal zinc for the two levels of dietary energy. Urinary calcium and magnesium were also significantly higher w h e n the diet provided 1780 kcal though, on the other hand, urinary zinc was significantly higher when the diet provided 2680 kcal (P 0.05). Urinary calcium and magnesium correlated negatively, whereas urinary zinc correlated positively, with the dietary energy intake (P~ ( 0 . 0 5 ) . Dietary energy intake has a significant effect on the mineral balance of the subjects.
*Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
93
Vol. 8, 1985
94
A t i n m o et aL
Index Entries: Dietary energy intake, and Zn, Ca, and Mg balance; mineral balance, and dietary intake; calcium, dietary intake and balance; magnesium, dietary intake and balance; zinc, dietary intake and balance.
INTRODUCTION Increasing attention is being focused on the effect of dietary components on the absorption and utilization of essential minerals. The effect of dietary protein on zinc, calcium, and magnesium has been extensively studied (1-3). On the other hand, very little work has been d o n e in the direction of relating calorie intake to mineral balance. Mahalko et al. (3) found that there was a statistically significant increase in urinary calcium from a relatively modest increase in dietary protein. Walker and Linkswiller (4) found that increased protein intake caused an increase in urinary calcium, thereby resulting in impaired calcium balance. Total calorie intake has also been found to affect calcium balance. In their various studies, Brown et al. (5), Leverton et al. (6), Young (7), and Young et al. (8), found that young w o m e n fed weightreducing diets exhibited a reduced calcium retention and in most cases a negative calcium balance. Decreased calcium absorption (5) and increased calcium excretion (7) were observed during the periods of low calorie intake, or possibly the decreased proportion of protein in the diet, was not clear. The effect of dietary protein on magnesium balance has also been demonstrated. Schwartz et al. (8) demonstrated that high protein intake in the presence of adequate magnesium intake led to negative magnesium balance in nonpregnant women; but the level of energy intake in the study was not indicated. Romualda et al. (10) in their studies related calorie content of diet to their m a g n e s i u m content. They concluded that a diet supplying an average of 3000 kcal d would contain about 342 m g of magnesium, but they failed to highlight what the m a g n e s i u m status of the subjects is likely to be. Jourdan (11) concluded that-both urinary calcium and magnesium excretions were depressed with calcium intake. The zinc content of a diet has also been related to the protein content (12). Greger and Snedeker (1) observed a significant increase in both fecal and urinary zinc excretions w h e n subjects were fed high protein diets. Dietary protein has also been found to affect the absorption of zinc. Greger and Snedeker (1) and Van Campen and House (13) observed a significant increase in apparent absorption of zinc w h e n subjects were fed high levels of dietary intake. However, Price et al. (14), Meiners et al. (15), and Colin et al. (16), working with h u m a n subjects, found that variation in dietary protein levels did not consistently affect apparent absorption and retention of zinc.
Biological Trace Elernent Research
VoL 8, 1985
Energy Intake and ~lineral Balance
95
Although very little work has been carried out to relate calorie intake directly with zinc balance, Spencer and Samachsen (17) observed that urinary zinc excretion rose to high levels during total starvation (no calories). In view of the findings above, this study was designed to investigate the direct effect of a moderate change in calorie intake on zinc, calcium and magnesium balance in young women fed on a habitually consumed diet.
MATERIALS AND METHODS Subjects and ExpeHrnental Design Thirteen female students of the University of Ibadan volunteered to participate in the study. The subjects had no known metabolic disorders. Their mean body weight was 53 kg. Subjects were not confined within the laboratory during the study. However, they were required to consume all their meals at the metabolic facility during supervised time periods, to weigh themselves before breakfast under standardized condit-ion (post voiding and minimal clothing) using Salter Scale and to collect all fecal and urine samples in designated containers. Blood samples were taken at the beginning and end of each experimental diet period. All the subjects were students, and they continued to attend classes regularly. They limited their participation in rigorous activities during the study. The balance study consisted of two experimental diet periods each of 10 d duration. Two different levels of energy (low and high) were fed, while protein intake was adequate based on a previously determined minimum nitrogen requirement (2). The low and high energy diets contained 1780 and 2580 kcal/d, respectively, and the adequate protein intake 25 g/d (0.47 g/kg body wt). All subjects were on the low energy diet during the first experimental period after a 3-d break, they were placed on the high energy diet. The subjects received a protein-free diet on the first day of each experimental diet period.
DIET Diets were standardized based on food habitually consumed and meal patterns the subjects were accustomed to. The basal diet fed throughout the study contained 90 g bread, tea, 15 g sugar as breakfast, 300 g grated cassava (eba), 60 g stew, 15 g vegetable, and 20 g meat as lunch; and 300 g rice 60 g stew, and 20 g meat as dinner. The diet for the low energy intake was supplemented with one bottle of carbonated drink whereas that of high energy was supplemented with two bottles of carbonated drink, 30 g margarine, 15 g sugar, and 100 g caloreen (Table 1).
Biological Trace Element Research
VoL 8, I g85
96
A t i n m o et aL
TABLE 1 Experimental Diet--High and Low Energy Intake Average body weight Protein intake High energy intake Low energy intake
Breakfast Bread Tea Sugar Margarine Lunch
Stew Vegetable Meat
Amount, g
53 kg = 0.47 g/protein/kg body wt (or 25 g/protein/d) = 2556.72 kcal = 1704.48 kcal =
Protein, g
90
High energy, kcal 209.7 120 219 263.25 300 2.9 53.33 420 300 53.33 400 240 2581.51
15 (30)~ 30 300 60 15 20
--0.75 0.88 0.5 4.0
209.7 . 60 -263.25 300 2.9 53.33
300 60 20 100b 1 Bottle
6.9 0.88 4.0 --24.93
420 300 53~ -120 1782.51
.
7.02
Low energy, kcal
.
.
Dinner
Rice Stew Meat Caloreen Soft drinks Total:
"High energy intake. bGlucose polymer.
ANALYSES Food, fecal, and urine samples were collected and stored in labeled plastic containers. Blood samples were collected into heparinized bottles. Containers for samples had been previously w a s h e d with d e t e r g e n t (Teepol), soaked in 1N HC1 overnight to remove soap residue, a n d t h e n rinsed thoroughly in deionized water. Fecal marker (camine) was administered to subjects after dinner on days 6 and 11 of each experimental period to mark the beginning and e n d of the collection period. Feces w e r e composited accordingly, w h e r e a s urine samples were composited daily. Food samples were collected daily from days 6 to 10 of each e x p e r i m e n t a l period. The 5 g fecal samples were pre-ashed. The ashed samples w e r e diluted in 50 mL volumetric flasks with 10 mL of 3N HC1 a n d m a d e to v o l u m e with deionized water. Aliquots were then taken a n d areas read on Perkin Elmer Atomic Absorption Spectrophotometer (AAS) Model Biological Trace Element Research
Vol. 8, 1985
Energy Intake and Mineral Balance
97
4000. Food samples were digested using 25 mL of 69% HC1. The samples were then heated for 5 rain and allowed to simmer for another 5 min. The samples were then filtered into sample bottles using W a t e r m a n Filter Paper No. 1. Samples were then read on the AAS for zinc. For calcium and magnesium, 5 mL samples were taken, 2 mL 1% l a n t h a n u m chloride solution was a d d e d in 100 mL volumetric flasks, and then m a d e to volume. Readings w e r e taken using AAS. Urine samples were diluted in the proportion of I part of urine plus 4 parts of deionized water, and into 0.1 mL of urine, 20 mL deionized water was added, and read on AAS for zinc and m a g n e s i u m , respectively; 2 mL of urine was made up to 10 mL with l a n t h a n u m chloride solution and the calcium concentrations w e r e then read on the AAS. Serum samples were also diluted in the proportion of 1:4 for zinc, 1:50 for m a g n e s i u m , and 0.25 of serum to 4 mL of deionized water p l u s 0.5 mL of l a n t h a n u m chloride and m a d e up to 5 mL with deionized water for calcium. The samples were read on the AAS~
RESULTS There was a reduction of 1.4 kg in the m e a n body weights of subjects during the low energy phase, whereas an increase of 0.6 kg was observed during the high energy diet. The diets were analyzed and found to contain 5.28 mg zinc, 216.8 m g calcium, and 364.3 m g magnesium. Fecal zinc was higher than the level of dietary zinc fed to subjects in the study. M e a n fecal zinc (mg) was higher during the high e n e r g y diet (7.2 • 2.9 vs 5.8 m 2.6). A positive correlation (r = 0.2) was observed b e t w e e n the dietary intake of energy and fecal zinc. However, the effect was not statistically significant (P ( 0 . 0 5 ) . Fecal calcium was significantly lower (P ( 0 . 0 5 ) during the high energy phase. A nonsignificant negative correlation (r = -0.12) was observed bet w e e n energy intake and fecal magnesium. There was a steady reduction in the urinary zinc output during the low energy phase. The level of urinary zinc fell from 0.5 mg/d on d 1 to 0.3 mg/d on d 10. On the other hand, a persistent rise was observed during the high energy diet. The level rose from 1.8 mg on d 1 to 2.5 mg/d on d 10. Dietary energy had a significant (P ( 0 . 0 5 ) effect on urinary zinc losses of the subjects. Dietary energy also had a significant effect on urinary calcium. Urinary calcium losses were significantly (P < 0.05) higher during the low energy phase. M a g n e s i u m excretion in urine was also significantly higher during the low energy intake (P ( 0 . 0 5 ) . Table 2 shows the regression equation of the dietary energy and urinary losses of the minerals. It can be observed from the table that urinary Biological Trace Element Research
Voi. 8, t 985
98
A t i n m o et aL
TABLE 2 Simple Regression and Correlation Between Dietary Energy Intake and Urinary Zn, Ca, and Mg Minerals
Regression equation ~
r
pb
Zinc Calcium Magnesium
Y = 0 . 0 9 X - 2.7 Y = 0.921X + 118.73 Y = 55.6 - 0.20X
0.92 -0.77 -0.93
0.05 0.05 0.05
"Y = level of dietary e n e r g y intake, bp = level of significance of the correlation coefficient (r).
zinc is positively correlated to dietary energy intake, whereas urinary caicium a n d m a g n e s i u m are negatively correlated to dietary e n e r g y intake. Six subjects were in positive zinc retention during the low e n e r g y diet w h e r e a s only one subject was in positive zinc retention during the high e n e r g y diet. Mean apparent retentions were negative for both levels of dietary energy intake (-0.91 and -4.08 mg/d for the low and high energy diets, respectively) (Table 3). More zinc was retained during the low e n e r g y diet. Dietary energy intake had a significant effect on the apparent retention of zinc in the subjects (r = 0.408, P < 0.05). All subjects were in negative Ca retention during the two levels of dietary energy intake. A p p a r e n t calcium retention was significantly d e p e n d e n t on the energy intake (r = 0.35, P < 0.05). A p p a r e n t m a g n e s i u m retention was significantly lower (P < 0.05) d u r i n g the low energy diet compared to the high energy phase. Eight subjects were in negative balance during the low energy phase, w h e r e a s all subjects were in positive balance during the high energy phase. Dietary e n e r g y was significantly correlated (r = 0.90, P < 0.05) with magnesium retention. There was no significant difference between the serum zinc levels for the two energy phases and also w h e n values were compared with the value at the beginning of the study. Moderate increase in dietary e n e r g y intake had no effect on serum zinc levels. A slightly higher increase (0.2 rag%) was observed in s e r u m calcium d u r i n g the high energy diet, but the effect was not significant. Serum m a g n e s i u m was equally not affected by the level of dietary e n e r g y intake, though a slight decrease in serum m a g n e s i u m was observed at the end of the high energy diet.
DISCUSSION The loss of weight observed in the subjects was a result of the reduction in the energy intake of the subjects. To meet the energy n e e d of tissues, it is possible that b r e a k d o w n of muscle protein occurred, leading to s u b s e q u e n t loss of weight and a reduction in the mid-arm circumference, Biological Trace Element Research
Vol. 8, ]985
Energy Intake and ~ineral Balance
99
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