Having one too many protein powders could send you to an early grave, a major review has found.
Fitness gurus on TikTok and Instagram routinely urge followers to increase their protein intake to aid weight loss and build muscle.
The craze has led to a boom in protein products, such as shakes, bars and powders, with 56 per cent of UK consumers seeking protein-rich food and drink, according to a 2024 study.
Now, a review of more than 350 papers suggests that cutting back on protein could reduce weight, fight heart disease and, ultimately, extend lifespan.
The authors, from the University of Wisconsin–Madison, said protein restriction could do this by improving metabolism, reducing inflammation and limiting the damage to cells that triggers fast ageing.
Experts agree that protein is a crucial component of a healthy diet. The nutrient helps repair and build muscle fibres, organs and connective tissue.
However, previous studies have found that eating less of it can extend the lifespan of flies and rodents.
Several recent clinical trials in humans have also shown that reducing protein intake can reduce weight and stabilise blood sugar levels.
A new review suggests that cutting back on protein could have greater health benefits and could, in some cases, extend lifespan
Interestingly, this was the case even though protein-restricted individuals tended to eat more total calories.
The latest review, published in the journal Cell Press Blue, identified several potential explanations for why reducing protein intake may be associated with health benefits.
Scientists believe a hormone called fibroblast growth factor 21, which rises when protein intake is low, can increase the body’s energy expenditure, improve blood sugar control and reduce inflammation.
However, experts cautioned that much of the evidence comes from animal studies, meaning the findings may not translate directly to humans.
Studies in mice have shown that animals with higher levels of this hormone lived longer than normal mice, and the benefit was more pronounced in male mice than female mice.
Eating less protein is known to raise this hormone level in humans as well.
The review also highlights several amino acids, the building blocks of protein, that appear to drive many of these negative effects.
Studies show that consuming too much of these amino acids could trigger biological processes that promote growth, increasing the risk of obesity, inflammation and other age-related diseases.
‘It’s absolutely crystal clear that there are benefits of protein to muscle growth and exercise response of active individuals,’ said the paper’s corresponding author Dudley Lamming from the University of Wisconsin-Madison.
‘But because most people are relatively sedentary, many people are likely consuming more protein than they actually need, which probably has negative health consequences.’
‘These studies show that the amount of protein sedentary people are eating today may have negative health consequences, at least at the population level,’ Mr Lamming added.
He says that while some people, like pregnant women and some older adults, have higher protein needs, for most sedentary adults, protein-fortified food may not provide the health benefits people expect.
Mr Lamming notes that athletes often consume large amounts of protein without developing metabolic diseases. He suspects that regular exercise, perhaps by using protein to build strong, healthy muscles, protects them from the negative health effects.
‘Recent recommendations have encouraged people to eat more protein, but they’ve also encouraged people to exercise more,’ Mr Lamming said.
‘We probably need to personalise protein recommendations based not just on age, but also on how physically active people are.’
However, not everyone is convinced by the findings.
Prof Paul Greenhaff, Professor of muscle metabolism at the University of Nottingham, notes that the review is primarily based on rodent and insect research – not humans.
‘Rodents and insects are not representative models of human ageing,’ he says.
In the UK, an estimated 66 per cent of adults are either overweight or living with obesity, which increases the risk of multiple long-term conditions including cardiovascular disease, liver disease, type 2 diabetes and at least 13 types of cancer.
The NHS recommends that to stay at a healthy weight, the average woman should eat 2,000 calories a day, while men should aim for 2,500 calories a day.
However, studies suggest that the average British man eats closer to 3,119 calories per day, while the average woman chews through around 2,393 calories.
UK guidelines recommend that healthy adults eat 0.75g of protein for each kilogram of body weight every day. This equals about 45g daily for a 60kg (9.4st) woman or 55g daily for a 75kg (11.8st) man.
Some experts have warned that very high protein intakes may place additional strain on the kidneys, particularly in people with existing kidney disease.
