Osteoporos Int DOI 10.1007/s00198-016-3504-z
LETTER
Evidence does not support the alkaline diet T. R. Fenton 1 & C. J. Fenton 2
Received: 11 December 2015 / Accepted: 21 January 2016 # International Osteoporosis Foundation and National Osteoporosis Foundation 2016
Dear Editor, We read the review paper BLife-course approach to nutrition^ [1] with interest but are concerned about the quality of critical review in the selection of references. In particular, we are writing about the section of the paper that promotes the Balkaline diet^ as a possible approach to preserving bone health. The one randomized controlled trial of the alkaline diet that evaluated bone mineral density after 2 years on the diet and actually used food (increased fruit and vegetables) as the intervention to alter the diet acid load did not provide any evidence in support of this diet for bone health [2]. The researchers observed no difference in any outcome, including bone mineral density and bone turnover markers over the Balkaline^ intervention [2]. In other words, this one direct high-quality assessment of the alkaline diet did not support the alkaline diet as beneficial for bone health. The authors cited potassium citrate randomized controlled trials in support of the diet. However, evaluations of potassium salts are not evaluations of dietary changes or an assessment of this diet. It is possible that potassium citrate has an anabolic effect on bone, but this does not justify the promotion of dietary changes. A response to this letter can be found at doi: 10.1007/s00198-016-3505-y. * T. R. Fenton [email protected]
1
Department of Community Health Sciences, Institute of Public Health, Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Canada
2
Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, Canada
They cited several cell culture studies as direct evidence of the use of alkali to promote bone health. Two of the cell culture studies evaluated the effects of an ambient pH of 7.0, which is not compatible with human physiology. Another cell culture study examined the effect of a pH of 7.4 versus 7.5 and 7.6 on bone. Even though these pH are theoretically compatible with human physiology, we lack any evidence that the alkaline diet changes can actually alter blood pH to that degree. A carefully designed randomized trial of the alkaline diet revealed that blood pH increased only to an average of 7.44 or an increase of 0.014 units [3]. Cell culture studies are useful for hypothesis generation but should not be considered evidence of an intervention’s effectiveness. So to summarize, the evidence cited in support of the alkaline diet in the paper is insufficient support and contradictory to stronger evidence. Furthermore, the authors dismissed high-quality research that does not support their hypothesis. The authors dismissed our systematic review [4] with the claim that we did not weight for sample size. However, this claim is incorrect. In fact, we weighted each study for sample size, as noted in the original publications of our meta-analyses of the randomized controlled trials of acid load on calcium metabolism [5, 6]. Meta-analyses, by definition, cannot be conducted without weighting for sample size since they produce weighted averages, or in the case of a continuous exposure such as diet acid load, a weighted regression analysis [7, 8]. The current state of evidence is such that we cannot support the alkaline diet. High levels of confidence in the evidence are needed before we should recommend any restrictive diet, including the alkaline diet. Restrictive diets can be hazardous to health through under-nutrition or the development of eating disorders such as orthorexia [9, 10].
Osteoporos Int Compliance with ethical standards Conflicts of interest None.
References 1.
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Mitchell PJ, Cooper C, Dawson-Hughes B, Gordon CM, Rizzoli R (2015) Life-course approach to nutrition. Osteoporos Int 26(12): 2723–42. doi:10.1007/s00198-015-3288-6 Macdonald HM, Black AJ, Aucott L, Duthie G, Duthie S, Sandison R, Hardcastle AC, Lanham New SA, Fraser WD, Reid DM (2008) Effect of potassium citrate supplementation or increased fruit and vegetable intake on bone metabolism in healthy postmenopausal women: a randomized controlled trial. Am J Clin Nutr 88(2):465– 74 Buclin T, Cosma M, Appenzeller M, Jacquet AF, Décosterd LA, Biollaz J, Burckhardt P (2001) Diet acids and alkalis influence calcium retention in bone. Osteoporos Int 12(6):493–9 Fenton TR, Tough SC, Lyon AW, Eliasziw M, Hanley DA (2011) Causal assessment of dietary acid load and bone disease: a
5.
6.
7.
8. 9.
10.
systematic review & meta-analysis applying Hill’s epidemiologic criteria for causality. Nutr J 10:41 Fenton TR, Lyon AW, Eliasziw M, Tough SC, Hanley DA (2009) Meta-analysis of the effect of the acid-ash hypothesis of osteoporosis on calcium balance. J Bone Miner Res 24(11):1835–40 Fenton TR, Lyon AW, Eliasziw M, Tough SC, Hanley DA (2009) Phosphate decreases urine calcium and increases calcium balance: a meta-analysis of the osteoporosis acid-ash diet hypothesis. Nutr J 8: 41 Greenland S, O’ Rourke K (2008) Meta-analysis. Page 652 in Modern epidemiology, 3rd ed. Edited by Rothman KJ, Greenland S, Lash T. Lippincott Williams and Wilkins. Philadelphia, PA Porta M (2014) A dictionary of epidemiology. 6th Ed. Oxford University Press, Oxford, UK Ramacciotti CE, Perrone P, Coli E, Burgalassi A, Conversano C, Massimetti G, Dell’Osso L (2011) Orthorexia nervosa in the general population: a preliminary screening using a self-administered questionnaire (ORTO15). Eat Weight Disord 16:e127–30 Portela de Santana ML, da Costa Ribeiro Junior H, Mora Giral M, Raich RM (2012) Epidemiology and risk factors of eating disorder in adolescence: a review. Nutr Hosp 27(2):391–401
LETTER
Evidence does not support the alkaline diet T. R. Fenton 1 & C. J. Fenton 2
Received: 11 December 2015 / Accepted: 21 January 2016 # International Osteoporosis Foundation and National Osteoporosis Foundation 2016
Dear Editor, We read the review paper BLife-course approach to nutrition^ [1] with interest but are concerned about the quality of critical review in the selection of references. In particular, we are writing about the section of the paper that promotes the Balkaline diet^ as a possible approach to preserving bone health. The one randomized controlled trial of the alkaline diet that evaluated bone mineral density after 2 years on the diet and actually used food (increased fruit and vegetables) as the intervention to alter the diet acid load did not provide any evidence in support of this diet for bone health [2]. The researchers observed no difference in any outcome, including bone mineral density and bone turnover markers over the Balkaline^ intervention [2]. In other words, this one direct high-quality assessment of the alkaline diet did not support the alkaline diet as beneficial for bone health. The authors cited potassium citrate randomized controlled trials in support of the diet. However, evaluations of potassium salts are not evaluations of dietary changes or an assessment of this diet. It is possible that potassium citrate has an anabolic effect on bone, but this does not justify the promotion of dietary changes. A response to this letter can be found at doi: 10.1007/s00198-016-3505-y. * T. R. Fenton [email protected]
1
Department of Community Health Sciences, Institute of Public Health, Alberta Children’s Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Canada
2
Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, Canada
They cited several cell culture studies as direct evidence of the use of alkali to promote bone health. Two of the cell culture studies evaluated the effects of an ambient pH of 7.0, which is not compatible with human physiology. Another cell culture study examined the effect of a pH of 7.4 versus 7.5 and 7.6 on bone. Even though these pH are theoretically compatible with human physiology, we lack any evidence that the alkaline diet changes can actually alter blood pH to that degree. A carefully designed randomized trial of the alkaline diet revealed that blood pH increased only to an average of 7.44 or an increase of 0.014 units [3]. Cell culture studies are useful for hypothesis generation but should not be considered evidence of an intervention’s effectiveness. So to summarize, the evidence cited in support of the alkaline diet in the paper is insufficient support and contradictory to stronger evidence. Furthermore, the authors dismissed high-quality research that does not support their hypothesis. The authors dismissed our systematic review [4] with the claim that we did not weight for sample size. However, this claim is incorrect. In fact, we weighted each study for sample size, as noted in the original publications of our meta-analyses of the randomized controlled trials of acid load on calcium metabolism [5, 6]. Meta-analyses, by definition, cannot be conducted without weighting for sample size since they produce weighted averages, or in the case of a continuous exposure such as diet acid load, a weighted regression analysis [7, 8]. The current state of evidence is such that we cannot support the alkaline diet. High levels of confidence in the evidence are needed before we should recommend any restrictive diet, including the alkaline diet. Restrictive diets can be hazardous to health through under-nutrition or the development of eating disorders such as orthorexia [9, 10].
Osteoporos Int Compliance with ethical standards Conflicts of interest None.
References 1.
2.
3.
4.
Mitchell PJ, Cooper C, Dawson-Hughes B, Gordon CM, Rizzoli R (2015) Life-course approach to nutrition. Osteoporos Int 26(12): 2723–42. doi:10.1007/s00198-015-3288-6 Macdonald HM, Black AJ, Aucott L, Duthie G, Duthie S, Sandison R, Hardcastle AC, Lanham New SA, Fraser WD, Reid DM (2008) Effect of potassium citrate supplementation or increased fruit and vegetable intake on bone metabolism in healthy postmenopausal women: a randomized controlled trial. Am J Clin Nutr 88(2):465– 74 Buclin T, Cosma M, Appenzeller M, Jacquet AF, Décosterd LA, Biollaz J, Burckhardt P (2001) Diet acids and alkalis influence calcium retention in bone. Osteoporos Int 12(6):493–9 Fenton TR, Tough SC, Lyon AW, Eliasziw M, Hanley DA (2011) Causal assessment of dietary acid load and bone disease: a
5.
6.
7.
8. 9.
10.
systematic review & meta-analysis applying Hill’s epidemiologic criteria for causality. Nutr J 10:41 Fenton TR, Lyon AW, Eliasziw M, Tough SC, Hanley DA (2009) Meta-analysis of the effect of the acid-ash hypothesis of osteoporosis on calcium balance. J Bone Miner Res 24(11):1835–40 Fenton TR, Lyon AW, Eliasziw M, Tough SC, Hanley DA (2009) Phosphate decreases urine calcium and increases calcium balance: a meta-analysis of the osteoporosis acid-ash diet hypothesis. Nutr J 8: 41 Greenland S, O’ Rourke K (2008) Meta-analysis. Page 652 in Modern epidemiology, 3rd ed. Edited by Rothman KJ, Greenland S, Lash T. Lippincott Williams and Wilkins. Philadelphia, PA Porta M (2014) A dictionary of epidemiology. 6th Ed. Oxford University Press, Oxford, UK Ramacciotti CE, Perrone P, Coli E, Burgalassi A, Conversano C, Massimetti G, Dell’Osso L (2011) Orthorexia nervosa in the general population: a preliminary screening using a self-administered questionnaire (ORTO15). Eat Weight Disord 16:e127–30 Portela de Santana ML, da Costa Ribeiro Junior H, Mora Giral M, Raich RM (2012) Epidemiology and risk factors of eating disorder in adolescence: a review. Nutr Hosp 27(2):391–401
