In the Journals

High-protein diet in middle age may increase risk for diabetes, cancer, mortality

A diet high or moderate in animal-derived protein may increase the risk for diabetes, cancer and all-cause mortality, according to study data published in Cell Metabolism.

Morgan E. Levine, PhD, of the Davis School of Gerontology at the University of Southern California, and colleagues assessed data from the Third National Health and Nutrition Examination Survey, which followed 6,381 adults aged at least 50 years for nearly 2 decades. The mean age of the study participants was 65 years.

Researchers defined high-protein intake as a diet deriving at least 20% of calories from protein, both plant- and animal-based. A diet including 10% to 19% of calories from protein was considered moderate, and a low-protein diet included less than 10% protein.

Overall, participants with high- and moderate-protein intake had higher risks for diabetes-related mortality compared with the low-protein intake group.

Researchers used Cox proportional hazard models to assess associations between protein consumption and age. They divided study participants into two groups: those aged 50 to 65 years and those aged at least 66 years. Among those in the younger group, higher protein intake increased the relative risk for death by 74% (HR=1.74; 95% CI, 1.02-2.97). They were four times more likely to die of cancer compared with participants who had a low-protein diet (HR=4.33; 95% CI, 1.96-9.56). Further, participants in the younger age group who ate a moderate-protein diet were three times more likely to die of cancer than those with a lower protein intake (HR=3.06; 95% CI, 1.49-6.25).

Although the study findings show that high-protein intake during middle age can be harmful, high-protein intake may be beneficial for older adults. Protein controls insulin-like growth factor I, whose levels dramatically decrease after age 65 years and can lead to frailty and muscle loss, according to researchers.

Data showed that participants aged at least 66 years who consumed high or moderate levels of protein vs. low levels of protein had a reduced risk for mortality of 28% (HR=0.72; 95% CI, 0.55-0.94) and 21% (HR=0.78; 95% CI, 0.62-0.99), respectively. Additionally, high-protein consumption reduced risk for cancer mortality by 60% (HR=0.4; 95% CI, 0.23-0.71).

“The research shows that a low-protein diet in middle age is useful for preventing cancer and overall mortality, through a process that involves regulating IGF-I and possibly insulin levels. However, we also propose that at older ages, it may be important to avoid a low-protein diet to allow the maintenance of healthy weight and protection from frailty,” study researcher Eileen Crimmins, PhD, the AARP chair in gerontology at the USC Davis School of Gerontology, said in a press release.

Researchers found an association between the type of protein participants consumed and elevated risks for diabetes, cancer and all-cause mortality. Controlling for calories from animal-derived protein significantly diminished the correlation between total protein intake and all-cause and cancer mortality among participants aged 50 to 65 years. This suggests that high levels of animal proteins increase risk for mortality. Further, one’s risk may be decreased if protein comes from a plant-based source, according to researchers.

“The majority of Americans are eating about twice as much proteins as they should, and it seems that the best change would be to lower the daily intake of all proteins, but especially animal-derived proteins. But don’t get extreme in cutting out protein; you can go from protected to malnourished very quickly,” study researcher Valter Longo, PhD, the Edna M. Jones professor of gerontology at the USC Davis School of Gerontology, said in the release.

Disclosure: The researchers report no relevant financial disclosures.