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How much protein should you consume, and from which sources? An 18-year study concludes that it all depends on your age. Protein could give you a longer life, or put you in danger of cancer and diabetes.

A "healthy and balanced" diet is one of the keys to good health and a long life, but what exactly does that mean? Protein is a much-discussed issue in the diet world. Should you be on a high-protein diet to optimize your health, or is it best to keep your protein intake on the lower side? A newly published study sheds a fresh new light on that question. 

A study based on 18 years' worth of data reveals that a person's optimal protein consumption depends on their age. High levels of protein, and animal protein in particular, appear to be a bad idea for younger people. Yet, increasing protein levels helps to extend the life span of those individuals who are already past middle age. 

Published in the journal Cell Metabolism, the study used a national database that tracked the health and nutrition behaviors of 6,381 Americans over a period of nearly two decades. Lead author Valter Longo, who is the director of the University of Southern California's Longevity Institute, now has a definitive answer on protein: 

"Some have said for years that proteins are bad. That's half right and half wrong."

Protein Intake — Tailored To Your Age?

Are you ready for the details? You might be shocked, no matter what your age and protein consumption. 

Individuals between the ages of 50 and 65 on a diet in which protein made up 20 percent or more of their daily food intake were found to have engaged in rather risky behavior — but probably without knowing it. These people's risks of death gradually increased to a level comparable to the risk of smoking cigarettes over the study's 18-year tracking period. 

They were more than four times as likely to die from cancer or diabetes than those whose protein consumption was lowest, as well as twice as likely to die from any cause. Oops!

It might just be time to rethink how many of your daily calories consist of proteins, if you are under the age of 50!

Yet, folks over the age of 65 were found to benefit greatly from a high-protein diet! People in the older age group were 60 percent less likely to die from cancer and 28 percent less likely to die from any cause. 

The research team found that it didn't really matter if the rest of a protein-loving younger person's diet was made up mainly of carbohydrates or fats. What did matter was the source of protein. Subjects who got most of their proteins from plant-based sources like legumes and nuts had a lower risk of death from cancer than those who favored animal protein. A diet high in plant-based proteins wasn't associated with a higher overall mortality rate at all. 

Interestingly enough, the same was not true for people older than 65. For this age group, protein from any source can maintain weight and muscle mass — something that might be key to living a longer life. 

Growth Hormones And Cancer

The study team didn't just use data, either. They traveled to a small town in Italy where many people live exceptionally long lives, and also went to Ecuador to visit another long-living family with a congenital lack of a growth hormone linked to cancer. In addition, blood tests were taken from some of the study subjects as well as from lab mice.

All of that led the researchers to define a growth hormone called insulin-like growth factor-1 as playing an essential role in the development of age-related diseases including cancer. Mice with the highest levels of this hormone were much more prone to cancer, while those with the lowest levels (associated with a lower protein intake) had reduced cancer rates. 

The conclusion? Protein may be your friend or your enemy, but it's time to think about your dietary strategy before implementing it. 

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