© Vanessa Loring
August 9, 2026
Marianne Waldenfels
Protein is widely regarded as healthy – but is more always better? A new review challenges the high-protein trend and suggests that a consistently high protein intake may not be beneficial for everyone.
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Protein bars, protein yogurt, protein bread – over the past few years, protein has transformed from an ordinary nutrient into a health buzzword. Higher protein intake is said to support muscle building, keep you fuller for longer, and protect against muscle loss, especially in old age. But does the rule "the more, the better" actually hold true for protein?
A new review from the United States is calling that assumption into question. Researchers at the University of Wisconsin-Madison examined what influence protein intake might have on metabolism and the aging process.
Their findings do not suggest that a high-protein diet is fundamentally harmful for healthy people. However, they do challenge a widespread assumption: that eating more protein automatically delivers more health benefits.
The researchers are particularly interested in whether metabolism and aging may operate according to different biological rules than muscle maintenance. In other words: could the amount of protein that is optimal for muscles simultaneously influence aging processes?
With that question in mind, the authors explored whether a lower protein intake – or the targeted reduction of specific amino acids – could potentially slow down aging processes.
Before this leads to new dietary recommendations, it is worth taking a closer look at the data. The paper does not present new findings from a clinical study in humans.
Instead, Bailey A. Knopf and Prof. Dudley W. Lamming and their team at the University of Wisconsin-Madison have compiled previously published research – ranging from cell experiments and animal studies to observational studies and early randomized intervention studies in humans.
Their goal was to understand why a lower protein intake is repeatedly associated with slower biological aging across a variety of animal models.
Lamming himself also tempers overly high expectations. Speaking to the specialist publication , he stresses that an adequate protein intake for muscle building and recovery is beyond question. His criticism is aimed instead at a broader dietary trend: many predominantly sedentary people today consume significantly more protein than they actually need.
This is precisely where the real debate begins. Hardly anyone disputes that protein is essential. What remains open is whether a persistently high protein intake always benefits metabolism, or whether at some point other biological processes take precedence.
There is no simple threshold. How much protein a person needs depends on a range of factors, including age, body weight, physical activity, and health status.
For healthy adults aged 19 to under 65, the German Nutrition Society (DGE) recommends 0.8 grams of protein per kilogram of body weight per day. From the age of 65, the estimated requirement rises slightly to 1.0 gram per kilogram of body weight.
However, no fixed upper limit can be derived from these recommendations beyond which protein automatically becomes harmful for healthy people. The new review likewise does not show that, for example, 1.5 or 2 grams of protein per kilogram of body weight would be fundamentally dangerous.
The more important question is a different one: does a persistently high protein intake provide any additional health benefit once individual needs are already met? Particularly for people who exercise little and already get enough protein through their regular diet, the researchers question the widespread notion that "more is better."
Why might eating less protein influence aging? There is no clear answer yet. What is clear, however, is that protein is far more than just a building block for muscles. It also appears to influence metabolic processes that may play a role in healthy aging.
The hormone FGF21 may be an important piece of the puzzle. In mice, its secretion increases when they receive less protein. At the same time, they burn more energy and respond better to insulin. When the hormone is absent, many of these positive effects disappear.
Other biological processes also appear to respond to a lower protein intake. The researchers found indications that cell repair, inflammatory processes, and the activity of certain genes may all be affected. Which of these mechanisms are actually decisive in humans, however, remains unclear.
The hypothesis rests primarily on animal studies. In many models, animals fed a lower-protein diet lived longer and stayed healthier in old age. Whether these findings translate to humans, however, is still an open question.
Could the debate be focused on the wrong question? It may matter less how much protein we eat and more which amino acids it contains.
This is precisely where the authors see the most compelling aspect of their review. Amino acids are the building blocks of protein and serve different functions in the body. In animal studies, selectively altering individual amino acids was sometimes sufficient to produce effects on metabolism and lifespan similar to those seen with an overall lower-protein diet.
Branched-chain amino acids such as isoleucine, valine, and leucine are under particular scrutiny. Animal studies suggest that a lower intake of isoleucine in particular, and possibly valine, may be associated with more favorable metabolic effects.
Leucine, on the other hand, occupies a special position: it is a key signaling molecule for muscle protein synthesis and is therefore especially important for maintaining and building muscle mass.
This makes the picture complicated, but also scientifically intriguing. A diet that is optimal for muscle building does not necessarily promote the same biological processes as a diet linked to a longer lifespan in animal models.
For the researchers, this suggests that the protein debate will need to become more nuanced in the future. The key question may eventually no longer be simply how much protein we eat, but also what kind.
At first glance, the new review might seem to contradict current dietary recommendations. In reality, however, the two are addressing different goals.
As we age, the body responds less efficiently to dietary protein – a phenomenon experts call anabolic resistance. At the same time, the risk of losing muscle mass and strength increases.
To preserve muscle mass, mobility, and independence for as long as possible, an adequate protein intake therefore remains important in old age. Combining it with regular strength training is particularly beneficial.
The American review does not question this goal. Rather, it explores whether a persistently high protein intake could also influence metabolic and aging processes independently of muscle maintenance.
No – that cannot be stated as a blanket rule. The review provides no evidence that protein shakes, protein bars, or a high-protein diet are fundamentally harmful for healthy people. However, it does challenge the widespread belief that additional protein automatically translates into additional health benefits.
People who already meet their protein needs through a normal diet and exercise little have no reason to consume large additional amounts of protein for the sake of their health. The situation is different for older adults at risk of muscle loss or for athletes in intensive training, who may have a higher protein requirement.
That is precisely the key message of the new paper: how much protein makes sense depends on age, physical activity, muscle status, and overall health. "More is better" simply cannot be applied to protein as a universal rule.
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