Consuming too much protein could shorten lifespan and harm long-term health, according to a major review of more than 350 scientific papers published in the journal Cell Press Blue.
The review, led by researchers at the University of Wisconsin-Madison, found that restricting protein intake may improve metabolism, reduce inflammation and limit cell damage associated with accelerated ageing. Several clinical trials in humans have also shown that reducing protein intake can lower body weight and stabilise blood sugar levels, even when protein-restricted individuals consumed more total calories overall.
The findings come amid a booming market for high-protein products. According to a 2024 study, 56 per cent of UK consumers are actively seeking protein-rich food and drink, driven in part by social media influencers who promote high protein intake for weight loss and muscle building.
The hormone connection
The review identifies a hormone called fibroblast growth factor 21 as a key mechanism. This hormone rises when protein intake is low and is associated with greater energy expenditure, better blood sugar control and reduced inflammation. Studies in mice have shown that animals with higher levels of the hormone lived longer than normal mice, with the effect more pronounced in males than females. Eating less protein is known to raise this hormone level in humans as well.
The review also points to specific amino acids, the building blocks of protein, as potential drivers of harm. Consuming too many of these amino acids may trigger biological processes that promote growth, raising the risk of obesity, inflammation and other age-related diseases.
Sedentary adults the main concern
Corresponding author Dudley Lamming said the benefits of protein for muscle growth and exercise response in active individuals are well established. However, he said that because most people are relatively sedentary, many are likely consuming more protein than they need, which probably has negative health consequences.
Lamming noted that athletes frequently consume large amounts of protein without developing metabolic diseases, and suggested that regular exercise may protect them from the negative effects. He called for protein recommendations to be personalised based not only on age but also on physical activity levels. He also said that while some groups, such as pregnant women and certain older adults, have higher protein needs, protein-fortified food may not deliver the health benefits most sedentary adults expect.
Experts urge caution
Not all researchers are persuaded. Paul Greenhaff, professor of muscle metabolism at the University of Nottingham, said the review is primarily based on rodent and insect research and cautioned that such animals are not representative models of human ageing.
UK guidelines currently recommend that healthy adults consume 0.75g of protein per kilogram of body weight each day, equivalent to around 45g daily for a 60kg woman and 55g daily for a 75kg man. Some experts have also warned that very high protein intakes may place additional strain on the kidneys, particularly in people with existing kidney disease.
