The optimal level of protein in our diet has been a subject of great controversy in recent medical literature, and two studies out this month exemplify the controversy and the complexity of the situation. But in spite of their differences, both add to the growing body of evidence suggesting that a high-protein diet later in life can be an important part of maintaining health and longevity.

For years, doctors have advocated a low-fat diet as important to heart health, but recently this perspective has fallen under renewed scrutiny with the discovery of so-called “good fats” and the potentially greater impact of proteins and carbohydrates on metabolism and health. A new study in the Journal of the American Geriatrics Society found that among 1,007 elderly residents of Ohasama, Japan, men who ate the highest levels of animal protein were the least likely to experience a decline in “higher-level functional capacity”—that is, deterioration in learning, memory and problem solving. Conversely, researchers from the University of Southern California looked at the diet and medical history of 6,318 people over the age of 50, and found that those who ate the most animal protein were at an elevated risk of cancer and death from any cause, but only in the 50-65-year-old age group.

Paradoxically, people over 65 who ate the most protein were protected from cancer and all-cause mortality, although they still had a higher rate of death due to diabetes. Notably, in this study the risks were specific to animal protein—plant proteins appeared to have a much lower or negligible impact on disease—and the effect was attributed to a molecule called IGF-1, which stimulates growth. Overall, a protein-rich diet late in life appears to contribute to healthy aging, and could help people avoid disability and the need for long-term care in their twilight years.

(Sources: Cell Metab 2014 Mar;19(3):407-17; J Am Geriatr Soc 62:426–434, 2014.)