Vegetarians who don't cook their food have abnormally low bone mass, usually a sign of osteoporosis and increased fracture risk.
But a research team at Washington University School of Medicine in St. Louis also found that raw food vegetarians have other biological markers indicating their bones, although light in weight, may be healthy.
Fontana and colleagues studied 18 strict raw food vegans ages of 33 to 85.
All ate a diet that not only lacked animal products but also included only raw foods such as a wide variety of vegetables, fruits, nuts, seeds, sprouted grains and legumes, dressed with olive oil.
In both groups, Fontana's team measured body mass index, bone mass, bone mineral density, markers of bone turnover, levels of vitamin D and inflammatory markers such as C-reactive protein and insulin-like growth factor 1 (IGF-1).
Those on the raw food diet had lower body mass indices and significantly lower bone mass in important skeletal regions such as the hip and lumbar spine, sites where low bone mass often means osteoporosis and fracture risk.
The raw food group also had less inflammation, indicated by low levels of C-reactive protein, which is made by the liver as a response to inflammation in the body.
High levels of IGF-1 have been linked to risk of breast cancer and prostate cancer.
And in spite of the fact that the raw food group didn't drink milk or eat cheese, they had higher vitamin D levels than people on a typical, Western diet.
"I thought vitamin D might be a problem for them, but it was not."
Fontana also measured levels of the hormone leptin, which seems to play an important role in the regulation of bone metabolism.