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Plant-based Diets and Fracture Risk

By December 17, 2020 No Comments
Plant-based Diets and Fracture Risk

Recent research raises concerns that plant-based, and especially vegan diets, increase fracture risk.1 If indeed this is the case, consuming soyfoods might help offset any potential vulnerability.

The main research in question is the EPIC-Oxford study in the U.K. which involves approximately 55,000 (mostly white) participants, about 2,000 of whom are vegans (this cohort oversampled for vegetarians).1 Vegans had a 43% higher risk of fractures overall compared to nonvegetarians, as well as higher risks of hip, leg, and vertebral fractures. The biggest difference was for hip fractures; vegans were more than twice as likely as people who ate meat to break their hip. Before delving into this study, and possible reasons for the findings, it is informative to consider past research on this topic.

In 2009, a meta-analysis of 9 studies involving 2,749 participants found that bone mineral density (BMD) was approximately 4% lower in vegetarians than in omnivores at both the femoral neck and the lumbar spine.2 Compared with omnivores, vegans had a significantly lower lumbar spine BMD (6% lower), which was more pronounced than in lacto-ovo-vegetarians (2% lower). However, the authors of this analysis concluded that the lower BMD was clinically insignificant. A decade later, a systematic review and meta-analysis that included 20 studies and 37,134 participants also found that compared with omnivores, vegetarians and vegans had lower BMD at the femoral neck and lumbar spine. However, this analysis also found that vegans also had higher fracture rates.3 Thus, the U.K. results are not isolated findings.

Importantly, sub analysis of the results of the British study revealed that risk for all fractures combined was increased among vegan women (relative risk [RR], 1.53; 95% CI: 1.24, 1.88), but not among vegan men (RR, 1.18; 95% CI: 0.85, 1.62). Furthermore, risk was increased only among individuals with a body mass index (BMI) below 22.5. For perspective, the average BMI among nonvegetarians and vegans in the Adventist Health Study-2 was 28.3 and 24.1, respectively.4 Therefore, relatively few vegans are likely to be at increased fracture risk. The U.K. researchers noted that even after controlling for BMI, vegan fracture risk was still increased, although in a separate analysis of NHANES data, the lower BMD found among adult vegetarians was mostly explained by lower BMI and waist circumference.5

If the lower BMI does not account for all the increased fracture risk associated with vegan diets, what other factors may play a role? Vegans consume lower amounts of calcium and protein than nonvegetarians, which may put them at a disadvantage for maximizing bone health.6  Whether or not it is advantageous to consume higher-quality protein is an open question.7,8 The British study did not examine the impact of vitamin D (when combined with calcium) or vitamin B12 on fracture risk, the intake of both nutrients is associated with better bone health.9,10

Since the lower BMI of vegans is generally seen as a health advantage, focus should not be placed on encouraging vegans to gain weight, but on making sure vegans take steps to otherwise reduce their fracture risk. From a dietary perspective, many soy products may help in this regard.  Soy products provide high quality protein,11,12 and most soymilks are fortified with calcium, vitamin D, and vitamin B12. Tofu made using a calcium salt can be an excellent source of calcium, and increasingly, soy products such as meat analogues are fortified with vitamin B12.

In conclusion, some evidence suggests that vegans, in large part because of their lower BMI, are at higher risk of fracture. Individuals consuming completely plant-based diets should be able to take steps to improve their bone health. Adding soyfoods can be one of those steps.

References

  1. Tong TYN, Appleby PN, Armstrong MEG, et al. Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study. BMC Med. 2020;18(1):353.
  2. Ho-Pham LT, Nguyen ND, Nguyen TV. Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis. Am J Clin Nutr. 2009;90(4):943-50.
  3. Iguacel I, Miguel-Berges ML, Gomez-Bruton A, et al. Veganism, vegetarianism, bone mineral density, and fracture risk: a systematic review and meta-analysis. Nutr Rev. 2019;77(1):1-18.
  4. Orlich MJ, Singh PN, Sabate J, et al. Vegetarian dietary patterns and mortality in Adventist Health Study 2. JAMA internal medicine. 2013;173(13):1230-8.
  5. Karavasiloglou N, Selinger E, Gojda J, et al. Differences in bone mineral density between adult vegetarians and nonvegetarians become marginal when accounting for differences in anthropometric factors. J Nutr. 2020;150(5):1266-71.
  6. Rizzo NS, Jaceldo-Siegl K, Sabate J, et al. Nutrient profiles of vegetarian and nonvegetarian dietary patterns. Journal of the Academy of Nutrition and Dietetics. 2013;113(12):1610-9.
  7. Shams-White MM, Chung M, Fu Z, et al. Animal versus plant protein and adult bone health: A systematic review and meta-analysis from the National Osteoporosis Foundation. PloS one. 2018;13(2):e0192459.
  8. Itkonen ST, Paivarinta E, Pellinen T, et al. Partial replacement of animal proteins with plant proteins for 12 weeks accelerates bone turnover among healthy adults: A randomized clinical trial. J Nutr. 2020.
  9. Yao P, Bennett D, Mafham M, et al. Vitamin D and calcium for the prevention of fracture: A systematic review and meta-analysis. JAMA Netw Open. 2019;2(12):e1917789.
  10. Krivosikova Z, Krajcovicova-Kudlackova M, Spustova V, et al. The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet. Eur J Nutr. 2010;49(3):147-53.
  11. Hughes GJ, Ryan DJ, Mukherjea R, et al. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: Criteria for evaluation. J Agric Food Chemistry. 2011;59(23):12707-12.
  12. Reynaud Y, Buffiere C, Cohade B, et al. True ileal amino acid digestibility and digestible indispensable amino acid scores (DIAASs) of plant-based protein foods. Food Chem. 2020;338128020.
Dr. Mark Messina

Author Dr. Mark Messina

PhD in Nutrition, Executive Director, Soy Nutrition Institute. Expert in soyfoods and isoflavones.

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