Reducing a Single Amino Acid Extended Lifespan in Mice, Study Finds
Reducing a single essential amino acid in the diet extended the lives of mice by up to one-third, according to new U.S. research. The work suggests that carefully adjusting protein composition, rather than simply cutting calories, could strongly influence aging and long-term health.
The amino acid in question is isoleucine, one of three branched-chain amino acids that help the body build proteins. Because humans and other animals cannot produce isoleucine on their own, it must be obtained from foods such as eggs, dairy products, soy, poultry, pork, and beef.
Scientists at the University of Wisconsin and their collaborators used a genetically diverse group of mice to mirror the range of responses seen in human populations. At about six months of age, similar to a 30-year-old human, the animals were assigned to one of three diets and allowed to eat as much as they wanted.
One group received a standard control diet containing 20 common amino acids. A second group was fed a diet in which all amino acids were reduced by about two-thirds. The third group had only isoleucine reduced by a similar proportion, while levels of the other amino acids remained normal.
How cutting isoleucine changed aging
Mice that consumed less isoleucine lived longer and remained healthier for more of their lives than those on the control diet. Male mice experienced a lifespan increase of about 33 percent, while females saw an increase of roughly 7 percent, a smaller but still measurable benefit.
Across 26 different health indicators, the low-isoleucine mice showed signs of slower aging. They had better muscle strength and endurance, improved blood sugar control, less frailty, and fewer visible markers of aging, such as hair loss and reduced tail use.
In male mice, restricting isoleucine was also linked to less age-related prostate enlargement. These males were less likely to develop cancerous tumors, which commonly arise in the mixed mouse strains used to capture genetic diversity in the experiment.
Endocrinologist Dudley Lamming, who led the research, argued that the findings highlight how the composition of calories matters. He noted that different nutrients exert distinct biological effects that go well beyond their value as simple energy sources.
Unexpected effects on weight and metabolism
One of the most surprising results was how the mice handled calories. Animals on the low-isoleucine diet actually consumed more calories than control mice, yet they became leaner, with significantly lower levels of body fat and no increase in activity.
Measurements of energy use showed that these mice were burning more calories at rest. Their bodies shifted toward higher energy expenditure, which helped maintain a healthy body weight and appeared to protect against metabolic problems associated with aging.
These findings build on earlier work from 2016 to 2017 that linked higher dietary isoleucine intake to poorer metabolic health in people. In that survey of Wisconsin residents, individuals with higher body mass indexes tended to consume larger amounts of isoleucine than leaner participants.
Together, the human observational data and the new mouse experiments suggest that excess isoleucine may contribute to obesity and metabolic disease, while carefully lowering intake could provide benefits similar to those seen in calorie-restriction studies.
What this could mean for humans
Researchers are cautious about translating mouse results directly to humans, but they see potential in targeting specific amino acids to influence aging. They argue that isoleucine restriction, through diet or future drugs, could one day complement other strategies to extend human healthspan.
At the same time, cutting total protein too aggressively can cause loss of muscle mass, weakened immunity, and other problems. The team stresses that real-world interventions would need to lower isoleucine without broadly depriving the body of essential protein.
Because isoleucine is abundant in many high-protein foods, designing sustainable diets that reduce it while preserving overall nutrition is challenging. The controlled laboratory environment, where each pellet of food can be precisely formulated, is very different from everyday human eating habits.
Lamming suggested that choosing overall healthier, less processed foods may naturally reduce isoleucine intake to some degree. However, he and his colleagues emphasize that clinical trials are needed to test whether modest isoleucine restriction is safe, realistic, and effective for humans.
The level of isoleucine restriction in the mouse study was the same across strains and both sexes, but responses differed, especially between males and females. The authors note that future work must refine the dose and timing of restriction, as one nutritional approach is unlikely to suit every individual.
Ultimately, the scientists see isoleucine as a promising entry point for unraveling the molecular pathways of aging. By narrowing complex dietary effects down to one amino acid, they hope to uncover mechanisms that might be manipulated with targeted therapies, such as drugs that limit isoleucine signaling or uptake.
The research was published in the journal Cell Metabolism and adds to a growing body of evidence that nutrient composition, rather than simple calorie counts, may be a powerful lever for extending both lifespan and the number of years lived in good health.
