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High-protein diet in middle age can lead to early death

Teresa Tanoos's picture
Two new studies say that high-protein diets increase chances of dying from cancer and diabetes.

Although a high-protein diet may help you lose weight in the short-term, researchers in two new studies say that such a diet during middle age can literally be deadly by significantly increasing your chance of dying from cancer or diabetes.

In the studies, both published in the journal Cell Metabolism, researchers concluded that a low-protein diet is the best bet for a long and healthy life. Whether the protein is animal or plant-based counts too, as plant-based protein sources were less likely to raise the risk of death from cancer and diabetes.

One of the important findings of these two studies is that the typical high-protein diet that people go on to lose weight may work in the short-run, but in the long-run, such a diet can damage your health and shorten your lifespan

In the first study, led by Valter Longo from the University of Southern California, Longo and his research team discovered that eating a high protein diet raised the risk of middle-aged adults dying from cancer and diabetes. However, that did not hold true for older adults who may actually benefit from a diet with moderate amounts of protein.

In the second study, led by Stephen Simpson from the University of Sydney in Australia, he and his research team concluded that the best diet for longevity and health is one that is low in protein and carbohydrate-rich.

However, both studies indicate that calories aren’t the only factor involved. So is diet composition, especially as it pertains to how much and what kind of protein is consumed. In other words, both calories and diet composition are important factors in determining the health and length of an individual's life.

Prof. Longo said that the goal of their study was to find evidence that supports just how bad a high-protein diet really is, especially if it comes from animals. Indeed, he said that their findings showed that consuming too much protein was as bad for your health as smoking.

For their study, Prof. Longo and his research team evaluated data on over 6,800 American adults who participated in a national survey that assessed health and diet in the United States.

As a result, the researchers found that:

1. Among the participants, those aged 50 and over who consumed a high-protein diet were 4 times more likely to die from cancer or diabetes, and twice as likely to die from any cause over the next 18 years.

2. The participants who ate only moderate amounts of protein were 3 times as likely to die from cancer.

3. Among those whose high-protein diet was primarily from plants, the increased risk of dying from such diseases decreased or disappeared completely, but in those who were 65 and older it was just the opposite, with a high protein diet being tied to a 60 percent lower risk of death from cancer and a 28 percent lower risk of dying from any disease (results were similar for those who consumed only moderate protein amounts).

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For the study, the research team considered high-protein as a diet where at least 20 percent of the calories come from protein.

Due to the results of other studies, the researchers believe that growth hormone and the growth factor IGF-1 may be responsible for these findings.

For example, certain cell studies have suggested that amino acids, which protein contains, can interfere with protecting the cells, while also causing damage to DNA. Both these factors could explain the link between high-protein consumption and cancer.

For the second study, Prof. Simpson and colleagues studied how 25 different diets affected hundreds of mice in an effort to find out how various types of proteins, carbohydrates and fats impacted the energy, metabolism and lifespan of the mice.

As a result, they discovered that:

1. Mice on high protein/low carb diets experienced a decrease in food consumption, as well as reduced levels of body fat. However, they also had poor heart health, a lower metabolism and died earlier.

2. The mice with the poorest health that died earlier were those that consumed a low-protein, high-fat diet.

3. Mice on low-protein/high carbohydrate diets were the healthiest, despite consuming more calories and having increased body fat. Moreover, a diet low in calories did not lengthen the life of the mice, a finding that is the opposite of what previous studies have shown.

Prof. Simpson said that the findings of their study show “explicitly why it is that calories aren't all the same.” He added that more research is needed to find out where the calories come from and how they interact.

“This research has enormous implications for how much food we eat, our body fat, our heart and metabolic health, and ultimately the duration of our lives," he said.

Both studies suggest that the best diet for living a long and healthy life is one that has low- to moderate amounts of protein, is low in fat and is rich in complex carbohydrates, such as lots of fruits and vegetables.


1. Low Protein Intake Is Associated with a Major Reduction in IGF-1, Cancer, and Overall Mortality in the 65 and Younger but Not Older Population; Morgan E. Levine, Jorge A. Suarez, Sebastian Brandhorst, Priya Balasubramanian, Chia-Wei Cheng, Federica Madia, Luigi Fontana, Mario G. Mirisola, Jaime Guevara-Aguirre, Junxiang Wan, and others; Cell Metabolism online 4 March 2014; DOI: 10.1016/j.cmet.2014.02.006.

2. The Ratio of Macronutrients, Not Caloric Intake, Dictates Cardiometabolic Health, Aging, and Longevity in Ad Libitum-Fed Mice; Samantha M. Solon-Biet, Aisling C. McMahon, J. William O. Ballard, Kari Ruohonen, Lindsay E. Wu, Victoria C. Cogger, Alessandra Warren, Xin Huang, Nicolas Pichaud, Richard G. Melvin, and others; Cell Metabolism online 4 March 2014; DOI: 10.1016/j.cmet.2014.02.009.