Eating nutrient-rich foods can improve metabolic health and delay the ageing process. But what levels of macronutrients in the diet are appropriate to achieve this? To answer this question, Japanese researchers fed young and middle-aged male mice an isocaloric diet with varying levels of protein. They found that the mice were metabolically healthier when fed a diet with a moderate protein content. These results could provide valuable insights for the development of nutritional interventions and the improvement of metabolic health in humans.

Proteins to Improve Metabolic Health

As the saying goes, “you are what you eat”, the type of food we eat affects our health and longevity throughout our lives. In fact, there is a direct correlation between age-related nutritional needs and metabolic health. An optimal, age-appropriate diet can help to maintain metabolic health and therefore improve a person’s healthspan (time lived without disease) and lifespan. It is known that various dietary interventions involving different calorie and protein intakes improve health and longevity in rodents and primates. In addition, recent studies have shown a link between dietary macronutrients (proteins, carbohydrates, fats) and cardio-metabolic health and aging in mice. However, it is not known what amount of protein needs to be consumed to maintain a healthy metabolism.

In a new study published in GeroScience, a team of researchers led by Assistant Professor Yoshitaka Kondo of Waseda University in Japan investigated the amount of dietary protein required to improve metabolic health in mice as they aged. They recruited young (6 months old) and middle-aged male mice (16 months old) that were fed isocaloric diets of varying protein content (5 to 45%) for two months.

After two months, the effect of the different protein diets was assessed using measurements of skeletal muscle weight, liver and plasma lipid profiles and cluster analysis (SOM) of plasma amino acid profiles. Previous studies have shown that it is possible to minimize age-related mortality throughout life by altering the ratio of dietary protein to carbohydrate during the approach to old age in mice. However, it is still unclear what amount of protein should be consumed to maintain metabolic health as one approaches old age. The team observed that consuming a low-protein diet in middle-aged mice resulted in mild fatty liver with increased liver fat levels compared to young mice.

High-Protein Diet Could Extend Lifespan

In contrast, a diet with moderate protein content led to lower blood glucose concentrations and lipid levels in liver and plasma. These results suggest that a moderate protein diet (25% and 35%) kept both young and middle-aged mice metabolically healthier. When investigating the effects of different protein diets on plasma amino acid concentrations in mice of both age groups, the researchers found that plasma concentrations of individual amino acids varied with age and different dietary protein levels. This was further confirmed by a SOM analysis of the plasma amino acids. In addition, the plasma amino acid profiles determined by SOM analysis showed the correlation between the different protein intakes and the different amounts of hepatic triglycerides and cholesterol levels.

The protein requirement changes over the course of life: it is higher in younger, reproductive mice, decreases in middle age and increases again in older mice when protein efficiency decreases. The same pattern is likely to be observed in humans. Therefore, one could assume that a higher daily protein intake in meals promotes metabolic health in humans. In addition, an ideal macronutrient balance at any stage of life could also prolong health. To summarize, a balanced diet with moderate amounts of protein could be the key to a long and healthy life.