A Diet with Moderate Protein Levels May Promote Healthy Aging

Researchers uncover the optimum amount of protein required to promote a longer life and health span in mice, which could be similar in humans.

Protein is a macronutrient found in animal products such as meat, cheese, and eggs and plant-based food like beans, nuts, and seeds. Humans need protein to build muscle and organ tissues and maintain the healthy functioning of virtually every body system.

Moreover, research has shown that protein can help a person lose weight by maintaining muscle mass, decreasing hunger, and boosting metabolism.

In a mouse study published in GeroScience, researchers from Waseda University in Tokyo, Japan, discovered that moderate protein levels may also help maintain healthy metabolic health during aging and promote a longer life and health span.

To conduct the research, the scientists fed young and middle-aged mice a diet that contained the same number of calories with protein levels ranging from 5% to 45%. After two months on the diet, the scientists assessed the rodents' metabolic health through tissue and plasma samples and other health measures.

The results showed that mice fed a 5% to 20% protein diet — defined as a low protein diet — developed mild fatty liver, with middle-aged rodents showing more fat in the liver than young mice.

In contrast, a 25% to 35% protein or moderate protein diet appeared to reduce lipid levels in the rodents' liver tissue and blood and also lower blood sugar levels.

In addition, the scientists found that plasma amino acid concentrations differed among the mice and were dependent on age and protein levels in the diet.

The researchers concluded that a 25% to 35% protein diet is ideal to help maintain metabolic health in young and middle-aged mice.

In a news release, lead researcher Yoshitaka Kondo, an assistant professor at Waseda University, said, "Protein requirements change through the course of life, being higher in younger reproductive mice, reducing through middle age, and rising again in older mice as protein efficiency declines. The same pattern is likely to be observed in humans."

Kondo adds, "Therefore, it could be assumed that increasing daily protein intake in meals could promote metabolic health of people. Moreover, ideal dietary macronutrient balance at each life stage could also extend health span."

Notably, one researcher involved in the study is an employee of Nichirei Foods Corporation and dedicated to the functional evaluation of food. However, the remaining study authors declare no conflicts of interest.