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.