High-Protein Diet Linked to Cancer, Death, Study Finds

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Hold onto your post-workout shake: High-protein diets may help you lose weight, but they may also shorten your life, a new study reports.

After analyzing more than 6,000 adults, researchers found that those who ate a high-protein diet during middle age experienced higher rates of cancer, diabetes, and death. "The research shows that a low-protein diet in middle age is useful for preventing cancer and overall mortality," said study co-author Eileen Crimmins, the AARP chair in gerontology at the University of Southern California, in a press release.

But before you ditch your low-carb plan, the researchers added that the effect only seemed to last until the subjects were about 65 years old, at which point eating a higher-protein diet again became beneficial. The experts chalk it up to the fluctuations of the human growth hormone IGF-1 and how protein helps balance it: When we're young, we produce lots of IGF-1, which helps us grow but also increases the rate at which we age. The hormone levels out naturally around middle age, so an excess of protein before middle age only increases the aging effect of the hormones. When our IGF-1 starts to decline in old age, eating more protein can help protect against the levels dropping too low. 

Like many things in life, this may be another case of all things in moderation. The study seems to suggest that eating less protein through the middle years is a good way to protect our health. But it's not quite that simple, says Tori Cohen, R.D., director of food and nutrition services at Los Robles Hospital in California. 

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"You should focus on eating the protein that is right for you," she says. "For example, athletes will need more protein than less active people in order to prevent muscle wasting and to get enough B vitamins." She adds that it's a good idea to talk to a nutritionist if you have questions about how much is best for you to consume. Don't forget that protein is key for both building muscles and keeping you satisfied.

The Institute of Medicine recommends eating 0.8 to 1 grams of protein per kilogram of body weight each day. For example, a 140-pound woman would need between 51 and 63.5 grams of protein—an amount that Cohen says is easily covered if you eat some protein with each meal. 

"Protein deficiency is very rare in America," she says, adding that all this worry about protein obscures an even more important point: We do not eat enough plants, especially since plants have been shown in many research studies to lessen the likelihood of cancer, diabetes, and heart disease. A 2013 study published in the American Journal of Clinical Nutrition followed 71,000 Swedes over 13 years and found that those who don't get their daily allotment of fruits and veggies died an average of three years earlier than salad-lovers.

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Plus while animal protein seems to shorten lifespan, the study showed that was not true of eating plant-based protein such as lentils, legumes, edamame, or tofu. Cohen agrees, saying that she supports eating animal protein in moderation, but that it's also possible to get what you need from plants. 

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