Until now, medical opinion about the impact of vegetarian diets on bone health has been based on anecdotal evidence and a range of contradictory findings that sometimes rely on studies too small to be biologically relevant. A review and analysis of all relevant existing research shows that differences in bone mineral density between meat eaters and all vegetarians is 5%. The jury is still out on whether that translates into higher fracture risk.
Until now, medical opinion about the impact of vegetarian diets on bone health has been based on anecdotal evidence and a range of contradictory findings that sometimes rely on studies too small to be biologically relevant.
Researchers in Australia and Vietnam searched all peer-reviewed literature on the subject, selecting nine studies for analysis. The nine studies compared bone mineral density (BMD) of meat eaters and vegetarians from around the world, including 2,749 men and women.
Their results showed that people on vegetarian diets have BMD roughly 5% lower than non-vegetarians.
The study was led by Professor Tuan Nguyen from Sydney’s Garvan Institute of Medical Research and Dr Ho-Pham Thuc Lan from the Pham Ngoc Thach University of Medicine in Ho Chi Minh City, Vietnam. Their findings are published online today in the American Journal of Clinical Nutrition.
“There has been much debate surrounding this issue,” commented Nguyen. “Discrepancies in findings, inadequate clinical samples and poor comparative data have all contributed to the confusion.”
“Many studies tell us, for example, that countries with a high rate of vegetable consumption have a low risk of hip fracture. This implies that vegetable consumption is good for bone health.”
“Other studies have highlighted lower BMD measurements among vegetarians and have come to the opposite conclusion.”
“The truth, of course, encompasses many dietary and lifestyle factors. While BMD is important, it is not the only thing that contributes to fracture risk.”
Given the rising number of vegetarians (roughly 5% in Western countries) and the widespread incidence of osteoporosis (2 million people in Australia alone), the issue is worth resolving.
The team adopted a rigorous approach. Of the 922 peer-reviewed journal articles produced by their literature search, 9 met the criteria considered suitable for analysis. Studies had to be original, undertaken on people over 18, with vegetarian and non-vegetarian diets as factors and BMD as outcome.
The term ‘vegetarian diet’ included 4 types of vegetarian diet: semi-vegetarian (excluding meat); lactoovovegetarian (excluding meat and seafood); lactovegetarian (excluding meat, seafood and eggs but not milk and dairy products); and vegan (excluding all foods of animal origin).
Professor Nguyen and Dr. Thuc Lan believe the study has answered some important questions. “The term ‘vegetarian’ is loosely used, so we felt it was valuable to compare the impact of different vegetarian diets,” said Nguyen.
“We found there was practically no difference between meat eaters and lactoovovegetarians.”
“While there is a difference between meat eaters and vegans, that difference is small.”
“We conclude that vegetarians as a group have lower BMD than meat eaters as a group, but whether the difference translates into increased fracture risk has yet to be resolved.”