KEY POINTS:
Researchers studying a group of vegetarians whose diet was low in protein and calories found they had reduced blood levels of several hormones and other substances that have been tied to certain cancers.
A comparison group of distance runners also had lower levels of most of these substances, compared with sedentary adults with diets relatively high in protein from meat and dairy products.
But the low-protein group also had a potential advantage over the runners: lower levels of the insulin-like growth factor IGF-1, a body protein that helps cells grow.
The study was done by a team led by Dr Luigi Fontana, an assistant professor of medicine at Washington University in St Louis.
He and his colleagues report their findings in this month's American Journal of Clinical Nutrition.
The findings are based on a small sample of middle-aged adults, including 21 who had been vegetarians for at least two years.
They were compared with 21 long-time endurance runners the same age, and 21 sedentary adults who ate a typical American diet.
On average, the vegetarians ate just below the recommended daily amount of protein - 0.8 grams a kilogram of body weight.
The runners and the sedentary group ate much more than the recommended amount.
Fontana's team found that, compared with their sedentary counterparts, the runners and vegetarians had lower levels of several hormones and inflammatory proteins linked to cancer risk.
The low-protein group had lower levels of IGF-1 than the runners did, even though they were equally lean - suggesting an effect of diet and not just body weight, the researchers said.
IGF-1 levels in the sedentary group generally rose parallel with their protein intake.
"Many people are eating too many animal products," Fontana said.
He also singled out processed foods and sugars for criticism, and said people should eat more fruits and vegetables, whole grains, beans and fish.
Doing so could bring the amount of calories and protein eaten closer to recommended levels.
Fontana said: "We hope to further clarify what happens to cancer risk when we chronically eat more protein than we need."
- REUTERS
