A new review published in the science journal Cell Press Blue found that eating more protein is not always better.
For many adults who are not very physically active, eating less protein may support healthier ageing and could even help them live longer.
After reviewing more than 350 studies involving humans, mice and other organisms, the researchers found that reducing protein intake may improve metabolism, change how cells respond to nutrients, reduce cell damage and help cells function better.
However, the benefits depend on a person’s age, health and activity level.
“It’s absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals,” commented study corresponding author and America’s University of Wisconsin-Madison professor Dr Dudley Lamming.
“But because most people are relatively sedentary, many people are likely consuming more protein than they actually need, which probably has negative health consequences.”
Several recent human studies showed that eating less protein can help reduce body weight and body fat while improving fasting blood sugar levels.
The review also found that eating too much methionine, isoleucine and valine – amino acids that make up protein – may increase the risk of obesity, inflammation and other age-related diseases.
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At the same time, other studies suggest that eating more protein, especially along with regular exercise, can help older adults lose weight and reduce age-related muscle loss.
Researchers highlighted the role of a hormone called fibroblast growth factor 21 (FGF21), which increases when protein intake is reduced.
FGF21 helps the body burn more energy, improves blood sugar control and lowers inflammation.
Studies in mice showed that animals with higher FGF21 levels lived longer than normal mice, with the effect being stronger in males.
Lower protein intake also raises FGF21 levels in humans.
However, some people need more protein.
Pregnant women and some older adults have higher protein requirements.
On the other hand, for adults who are not physically active, protein-fortified foods may not provide the health benefits they expect.
Meanwhile, athletes often eat large amounts of protein without developing metabolic problems.
Researchers believe regular exercise may help the body use protein to build and maintain healthy muscles instead of contributing to health risks.
“Recent recommendations have encouraged people to eat more protein, but they’ve also encouraged people to exercise more,” Prof Lamming advised.
“We probably need to personalise protein recommendations based not just on age, but also on how physically active people are.” – dpa
