Eating less protein, not cutting calories, may be an easier path to a longer, healthier life for sedentary adults, according to a new scientific review.
While previous research has long tied calorie restriction to improved lifespan and lower rates of age-related disease, studies have found that many people have difficulty maintaining strict low-calorie diets.
A review of more than 350 studies published in the journal Cell Press Blue suggests that targeted protein restriction can deliver similar metabolic benefits without the need to cut calories.
Across the reviewed studies, lower protein intake was associated with better metabolism, altered nutrient signaling, reduced cellular damage and improved cellular maintenance, according to the published review.
Much of the benefit stems from a metabolic hormone known as fibroblast growth factor 21, or FGF21. Restricting protein triggers a surge in FGF21, which animal studies have shown can boost energy expenditure, reduce inflammation, improve blood sugar control and extend lifespan.
Researchers highlighted three essential amino acids that are building blocks of protein — methionine, isoleucine and valine. Under certain conditions, they may contribute to biological pathways associated with aging under certain conditions.
For people who don’t exercise regularly, high levels of these amino acids may keep certain growth-related processes constantly active. Over time, that stimulation can create cellular damage, systemic inflammation and weight gain.
“It’s absolutely crystal-clear that there are benefits of protein for muscle growth and exercise response of active individuals,” said Dudley Lamming, the paper’s corresponding author and a researcher at 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,” he added in the press release.
There were some limitations to the study findings. Because the paper is a scientific review rather than a new clinical trial, it identifies patterns across existing research but cannot establish cause and effect in humans, the researchers acknowledged.
Longer-term human studies are still needed to determine whether these metabolic benefits ultimately translate into increased lifespan, they noted.
The review emphasizes that protein needs are not one-size-fits-all, and that the findings should not be interpreted as a recommendation to consume inadequate amounts.
Physically active people and athletes process protein differently. Exercise helps to direct dietary amino acids toward building and repairing muscle instead of leaving excess amino acids to be processed by the body, the researchers noted.
High protein intake is also crucial for pregnant women and older adults who may face age-related muscle loss.
For the broader, largely inactive population, the findings suggest that public health guidelines should move away from sweeping recommendations and instead tailor protein targets to a person’s age and activity level.
