Low-protein, low-calorie dieters show lower levels of hormone linked to cancer

People who eat a low-protein, low-calorie diet have lower levels of a hormone linked to cancer compared to those who eat other diets, researchers have found.

Overweight people are at higher risk of developing post-menopausal breast cancer, endometrial cancer, colon cancer, kidney cancer and a type of esophageal cancer.

Now a study suggests eating less protein may help protect against cancers not directly linked to excess weight.

Dr. Luigi Fontana, a medical professor at Washington University, and his team compared participants in three groups:

• Lean men and women who ate a low-protein, low-calorie, raw food vegetarian diet.
• Lean men and women who did regular endurance running of about 77 kilometres per week and ate a standard Western diet.
• Sedentary people who consumed a standard Western diet high in sugars, processed refined grains and animal products.

"People on a low-protein, low-calorie diet had considerably lower levels of a particular plasma growth factor called IGF-1 than equally lean endurance runners," Fontana said.

"That suggests to us that a diet lower in protein may have a greater protective effect against cancer than endurance exercise, independently of body fat mass."

Each group included 21 people, who were matched for age, sex and other demographic factors. None were smokers or had diabetes, heart disease or other chronic illnesses.

Both the runners and the sedentary participants ate about 50 per cent more protein than recommended, the researchers report in the December issue of the American Journal of Clinical Nutrition.

While consuming 50 per cent more calories than recommended will likely lead to obesity, no one knows whether chronic over-consumption of protein also has a harmful effect, Fontana said.

The study is a "hypothesis-generating" paper pointing to a connection between dietary protein and population studies that suggest a link between blood levels of insulin-like growth factor and cancer risk, he added.

The team is planning more research to clarify what happens to cancer risk from eating more protein than recommended in the long term.