Is more protein always better?

High-protein products are becoming increasingly common in supermarkets. In the United States, 61 percent of consumers increased their protein intake in 2024. In 2019, that figure was 48 percent. Manufacturers responded by producing more high-protein foods. A new review questions the idea that more protein is always better.

Studying lower protein intake

The review brings together research on protein restriction and aging. In yeast, flies, and rodents, protein restriction extended healthspan. Several animal studies also found an increase in lifespan.

Short-term human studies also identified metabolic changes. A 43-day low-protein diet reduced body weight and fat mass. Fasting blood glucose also declined, despite a higher calorie intake.

In lean men, insulin sensitivity improved after five weeks. Energy expenditure also increased. Another study involved patients with metabolic syndrome and lasted 27 days. Participants had less body fat and improved insulin sensitivity. Blood glucose and lipid levels also declined.

Amino acid profile also matters

According to the review, total protein intake is not the only factor. Individual amino acids can also have different effects. The researchers focus particularly on methionine, isoleucine, and valine.

Restricting these amino acids replicated the effects of protein restriction in several studies. The researchers describe changes in metabolism and nutrient sensing. Mitochondria, cellular senescence, and the epigenome are also addressed.

However, the results vary considerably by amino acid. The organism studied and the dosage also affect the findings. Restricting some amino acids appears to be beneficial. Other studies instead report benefits from supplementation.

No general dietary recommendation

The optimal protein intake for healthy aging remains unknown. Much of the research on individual amino acids involved model organisms. Clinical research must determine what these findings mean for humans.

Protein restriction is also not suitable for every group. Pregnant women, growing children, and recovering patients may need more protein. The same may apply to athletes. Older adults also face a risk of deficiency due to reduced appetite, financial constraints, or social isolation.

Cell.com