You might have seen the recent news headlines proclaiming that “Vegetarian Diet Weakens Bones.” This headline, which was published by news sources all around the world, stemmed from an overview analysis (known as a “meta-analysis”) of nine published studies which compared the bone density of vegetarians and omnivores. From the way the news headline was written, you would think that the researchers had found compelling evidence that vegetarians had weaker bones, lower bone density, and increased risk of fracture. The research findings, however, found that vegetarians as a group had only a slightly lower bone density than omnivores and that this difference was neither clinically significant nor likely to result in increased fracture risk. Once again, the wise consumer is advised to look beyond the headlines and sort research facts from journalistic fiction.
The story for vegans (vegetarians who eat no flesh foods nor consume any animal products such as eggs or dairy) is a different issue. This new meta-analysis, as in previous individual studies, found that vegans exhibit significantly lower bone density than either vegetarians or omnivores. Vegans have also been noted to have lower body weight and reduced intakes of protein and calcium.
And what about the fracture risk of vegetarians and vegans? At the Center for Better Bones, our focus is on fracture risk, not bone density, and while this new study did not address fracture risk, other studies have done so. For example, in 2007, the large European EPIC–Oxford study reported the risk of fracture to be similar for meat eaters, fish eaters, and vegetarians, whereas vegans as a group had a 30% increased risk of fracture. I suspect that low body weight combined with sub-optimal intakes of protein, calcium, and bone-building minerals place vegans at higher risk of fracture, even though they, as other vegetarians, likely have a reduced acid load. This line of thinking is supported by the additional EPIC-Oxford finding that vegans who consumed more calories and at least 525 mg of calcium per day had a fracture rate nearly similar to egg- and milk-eating vegetarians and omnivores.
References:
Ho-Pham, LT, Nguyen, ND, Nguyen, TV. 2009. Effect of vegetarian diets on bone mineral density: A Bayesian meta-analysis. Am J Clin Nutr 90:1-8.
Appleby, P, Roddam, A, Allen, N and Key, T. 2007. Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford. Eur J Clin Nutr 61:1400-06.