High-protein diets can result in short-term weight loss, but may be as hazardous as smoking, leading to an increased chance of early death, according to a study by U.S. and Italian researchers that was published in the journal Cell Metabolism. The study found that people with diets high in meat, milk, cheese, and other animal proteins had four times the probability of dying of cancer than those who ate low-protein diets, a risk factor comparable to smoking.
The study also found that people who eat high-protein diets are several times more likely to get diabetes, and twice as likely to die early.
Researchers had never shown a definite correlation between a high-protein diet and mortality risk before this study, which tracked more than 6,300 people for 20 years. All participants were at least 50 years of age.
Plant-based proteins were not found to have the same effect as animal proteins. Study co-author Valter Longo, gerontology professor and director of the Longevity Institute at the University of Southern California says the best dietary change to make would be to lower the daily intake of all protein, but especially animal protein.
There is debate about how much protein belongs in a healthy diet. Several leading agencies recommend consuming about 0.8 grams of protein daily per kilogram of body weight during middle age. This amounts to 45-50 grams of protein per day for a 130-pound person.
People who consume moderate amounts of protein, typically defined as 10 to 19 percent of total calorie intake, are still at a 300 percent higher risk of cancer than those who get less than 10 percent of their calories from animal protein.
High-protein diets have been popularized by plans such as Atkins or Paleo diets, but even Americans who are not trying to lose weight eat more protein than advised. People who would never risk the hazards of smoking may think that they are doing the right thing for their health with a high-protein diet, but Longo says that most Americans already eat about twice as much protein daily as they should, and that it seems that lowering their daily intake of all proteins, especially those that are animal based, would be the best change to make. But he cautions not to cut out too much protein, due to the risk of malnutrition.
People over 65 may actually benefit from a higher protein diet. Protein helps control the IGF-I growth hormone, which helps bodies grow but makes them more vulnerable to cancer. IGF-I levels are reduced after age 65, causing frailty, weight loss, and illness. In the over-65 age group protein consumption was found to be protective.
A new Australian study from the University of Sydney’s Charles Perkins Centre supported the USC findings after studying the effects of protein, fat, and carbohydrates in mice. The research, demonstrated that weight loss achieved by high protein diets did not positively affect lifespan.
The Australian study also found that although people lose weight on a high-protein, low-carbohydrate diet, it did not lead to a longer life. A high carbohydrate, low-protein diet actually increased body fat, but resulted in better longevity and overall health.
Not all researchers agree with the study, saying that it was too small to provide any forceful conclusions. But aficionados of high-protein diets may lose enthusiasm if the hazards equal to smoking go along with them.
By Beth A. Balen