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Moderate Protein Diet Promotes Healthy Aging

Different plates of food, each with a protein source.
Credit: Shayda Torabi/ Unsplash
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We all know having a balanced diet is important to stay healthy. New research from Waseda University has started to unpick the optimum proportion of macronutrients for a diet that supports metabolic health as we age – starting with protein. The study is published in GeroScience.

Linking diet to “healthspan”

Over our lifespans, our nutrition needs change. By optimizing our diets according to what our bodies need (in relation to our age), we can maintain our metabolic health and thereby increase our “healthspan”, with healthspan referring to the length of time in our lives that we spend in good health.

Various diet-related interventions – such as caloric restriction and intermittent fasting have been shown to alter the life- and healthspans of rodents in animal studies, with further research linking lifespan and metabolic health to the consumption of dietary macronutrients.


Macronutrients are the nutrients that provide calories and energy necessary for growth and metabolism. Carbohydrates, proteins and fats are all macronutrients.

Lead researcher of the new study, assistant professor Yoshitaka Kondo, explains: “The optimal balance of macronutrients for ideal health outcomes may vary across different life stages. Previous studies show the possibility of minimizing age-specific mortality throughout life by changing the ratio of dietary protein to carbohydrates.”

The new study aimed to identify the ideal amount of protein needed in a diet that improves metabolic health in the approach to old age.

Getting the amount of protein right

In their new investigation, the team fed young and middle-aged mice diets with the same number of calories, but varying protein contents. The protein content in the diets ranged from 5% to 45% of the total calories consumed.

The mice were fed the diet for two months before various health measures, including skeletal muscle weight and liver and plasma lipid profiles, were recorded.

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A low-protein diet (defined as 520% of dietary calories) was associated with the development of mild fatty liver, accompanied by an increase in hepatic lipids seen in the middle-aged mice. However, the moderate protein diet (where protein made up 25–35% of the caloric intake) reduced both plasma and hepatic lipid levels and lowered blood glucose concentrations.

The researchers also analyzed the plasma amino acid concentrations of the mice, finding that the concentrations of individual amino acids in plasma vary with age and the protein content of the diet.

Overall, the study indicates that a moderate protein diet kept both young and middle-aged mice metabolically healthier. “The same pattern is likely to be observed in humans,” Kondo remarks.  “Therefore, it could be assumed that increasing daily protein intake in meals could promote the metabolic health of people.”


Reference: Kondo Y, Aoki H, Masuda M, et al. Moderate protein intake percentage in mice for maintaining metabolic health during approach to old age. GeroSci. 2023. doi: 10.1007/s11357-023-00797-3

This article is a rework of a press release issued by Waseda University. Material has been edited for length and content.