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Too much protein increases cancer risk

Earlier this week scientists reported a strong correlation between obesity and the risk of common cancers, such as cancer of the colon and breast cancer. Today, initial findings from a US study suggest that eating less protein could be a way to protect some people from cancers that are not directly associated with obesity.

The research is published in the December issue of the American Journal of Clinical Nutrition (2006, 84, 1456), shows that lean people on a long-term, low-protein, low-calorie diet or participating in regular endurance exercise training have lower levels of plasma growth factors and certain hormones linked to cancer risk. “However, 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,” says Luigi Fontana of Washington University, “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.”

“Our findings show that in normal weight people IGF-1 levels are related to protein intake, independent of body weight and fat mass,” Fontana says. “I believe our findings suggest that protein intake may be very important in regulating cancer risk.”

Fontana says most of us don’t eat nearly enough fruits and vegetables or enough whole-grains, cereals or beans. “Many people are eating too many animal products — such as meat, cheese, eggs and butter — as well as refined grains and free sugars,” he says. “Our intake of vegetables and fruits is low, and beans are vastly underconsumed in the U.S. and Europe these days.”

He believes diets would be healthier if we ate more whole grains, beans, fruits and vegetables and far fewer animal products. He recommends mostly fish, low-fat dairy products and, occasionally, some red meat. Such a diet would both cut total calories and reduce the amount of protein we consume to healthier levels.

“Eating too many calories increases our risk of developing obesity, diabetes, cardiovascular disease and of certain types of cancer related to obesity,” Fontana adds, “We hope to further clarify what happens to cancer risk when we are chronically eating more protein than we need.”

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