Even though there has been for some time concern on the part of experts that a vegetarian diet may have negative impact on bone health, until now that opinion has largely been based on anecdotal evidence and a range of contradictory findings which have often relied on studies which experts say are too small to be biologically relevant.
But now a new review by scientists from Australia and Vietnam of all the peer-reviewed literature on the issue has found that people on vegetarian diets have approximately 5% lower bone mineral density (BMD) than non-vegetarians.
The researchers selected nine studies for analysis which compared the BMD of 2749 men and women - meat eaters and vegetarians - from around the world and 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.
Professor Nguyen says there has been much debate surrounding this issue over the discrepancies in findings, inadequate clinical samples and poor comparative data, which have all added to the confusion.
Professor Nguyen says some of the research indicates that countries with a high rate of vegetable consumption have a low risk of hip fracture, which implies that vegetable consumption is good for bone health, while other studies have highlighted lower BMD measurements among vegetarians and have come to the opposite conclusion.
Professor Nguyen says the truth, encompasses many dietary and lifestyle factors and while BMD is important, it is not the only thing that contributes to fracture risk.
However the ever increasing number of vegetarians - around 5% in Western countries - and the widespread incidence of osteoporosis - 2 million people in Australia alone - means the issue demands some resolution.
For the study the team were rigorous - studies had to be original, undertaken on people over 18, with vegetarian and non-vegetarian diets as factors and BMD as outcome - and of the 922 peer-reviewed journal articles produced by their search, only 9 met the criteria considered suitable for analysis.
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 answers some important questions - Professor Nguyen says the term 'vegetarian' is loosely used, so they felt it was valuable to compare the impact of different vegetarian diets.
They found there was practically no difference between meat eaters and ovolactovegetarians and the difference between meat eaters and vegans, was small and reached the conclusion that vegetarians as a group have lower BMD than meat eaters, but say whether the difference translates into increased fracture risk has yet to be resolved.
Their findings are published online in the American Journal of Clinical Nutrition.