Raw Food Vegetarian Diet May Cause Low BMD Without Evidence of Increased Bone Turnover

Laurie Barclay, MD

March 28, 2005

March 28, 2005 -- People on a raw food (RF) vegetarian diet have low bone mineral density (BMD) but without evidence of increased bone turnover, according to the results of a small, cross-sectional study published in the March 28 issue of the Archives of Internal Medicine. The authors suggest that further study is needed to determine fracture risk.

"Because of their low calorie and low protein intake, RF vegetarians have a low body mass index (BMI) and a low total body fat content," write Luigi Fontana, MD, PhD, from Washington University School of Medicine in St. Louis, Missouri, and colleagues. "It is well documented that a low BMI and weight loss are strongly associated with low bone mass and increased fracture risk, while obesity protects against osteoporosis. However, the underlying mechanisms are not entirely clear."

The 18 volunteers studied included 11 men and seven women on an RF vegetarian diet for a mean of 3.6 years. Mean age was 54.2 ± 11.5 years. The authors compared body composition,

bone mineral content and density, bone turnover markers (C-telopeptide of type I collagen and bone-specific alkaline phosphatase), C-reactive protein, 25-hydroxyvitamin D, insulin-like growth factor 1, and leptin in serum in these RF vegetarians with the same parameters in a comparison age- and sex-matched group eating typical American diets.

Mean BMI was 20.5 ± 2.3 kg/m 2 in the RF vegetarians and 25.4 ± 3.3 kg/m 2 in the control subjects. Compared with the control group, the RF vegetarians had lower mean bone mineral content ( P = .003) and density of the lumbar spine ( P < .001) and hip ( P = .01 and P < .001, respectively). Both groups had similar serum C-telopeptide of type I collagen and bone-specific alkaline phosphatase levels. However, the RF group had higher mean 25-hydroxyvitamin D concentration ( P < .001) and lower mean serum C-reactive protein ( P = .03), insulin-like growth factor 1 ( P = .002), and leptin ( P = .005) than did the control group.

"A[n] RF vegetarian diet is associated with low bone mass at clinically important skeletal regions but is without evidence of increased bone turnover or impaired vitamin D status," the authors write. "Although low bone mass is a risk factor for fracture, bone quality also plays a role. It is therefore possible that RF vegetarians with a low bone mass may not have an increased incidence of fractures because of good bone quality."

Study limitations include small sample size, recruitment by advertisement, motivation of the RF vegetarians to confirm the beneficial effects of their diet, and inability to exclude the possibility that low bone mass could also be due to low peak bone mass rather than loss after institution of an RF diet.

"It will be necessary to follow up a large number of RF vegetarians for a sufficiently long period to determine whether they have an increased risk of developing fractures," the authors conclude.

The General Clinical Research Center, Diabetes Research and Training Center, and Clinical Nutrition Research Unit of the National Institutes of Health in Bethesda, Maryland, supported this study. The authors report no financial conflicts of interest.

Arch Intern Med. 2005;165:684-689

Reviewed by Gary D. Vogin, MD

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