Scientists have long studied whether changing what we eat can slow aging and extend healthy life.
Research from the University of Wisconsin School of Medicine and Public Health suggests that reducing one common part of dietary protein may have surprisingly large effects, at least in mice.
The nutrient is isoleucine, one of the amino acids the body uses to build proteins. The study, led by Professor Dudley Lamming, was published in the journal Cell Metabolism.
Isoleucine is an essential amino acid. This means the body cannot make enough of it on its own, so people must obtain it from food.
It is found in many protein-rich foods, including meat, fish, eggs, dairy products, soy and other plant foods. Isoleucine is needed for normal growth, tissue repair and other basic functions, so eliminating it from the diet would not be healthy.
The researchers were interested in a different question: could consuming less isoleucine, while still getting enough to meet the body’s needs, improve health during aging? Previous work has suggested that the amount and type of protein in the diet can influence metabolism and lifespan.
In the study, mice were given diets containing different amounts of isoleucine. Some animals received a diet with reduced levels, allowing the researchers to observe how the change affected health and survival as the mice aged.
The results were striking. Male mice eating less isoleucine lived about 33% longer, while female mice lived about 7% longer than comparison animals.
The benefits were not limited to lifespan. Mice on the reduced-isoleucine diet also showed several signs of better health, suggesting they were not simply surviving longer while becoming increasingly sick.
One surprising result involved body weight. The mice eating less isoleucine actually consumed more calories, yet they remained leaner than animals on the comparison diet.
This suggests that reducing isoleucine changed how their bodies handled energy. The effect was not simply caused by eating less food.
The animals also showed improvements in blood sugar control. Keeping blood sugar within a healthy range is important because poor glucose control is closely linked with metabolic diseases such as type 2 diabetes.
Male mice receiving less isoleucine also had less age-related enlargement of the prostate. The researchers observed other health improvements as well, including a lower occurrence of tumors.
Why would changing one amino acid have such broad effects? Scientists are still working out the answer, but amino acids do more than provide material for muscles and other tissues.
They can also act as signals that influence metabolism, growth and the way cells respond to nutrients. Changing the supply of a particular amino acid may therefore affect several biological pathways at the same time.
The researchers also examined information from people in Wisconsin. They found an association suggesting that leaner people tended to consume diets containing less isoleucine.
However, this human observation does not prove that eating less isoleucine caused people to be leaner or healthier. Human diets and lifestyles are far more complicated than the carefully controlled diets used in laboratory mice.
This is also why the dramatic lifespan results should be interpreted cautiously. A 33% increase in lifespan in male mice does not mean that a person can expect to live one-third longer simply by reducing meat, eggs or other foods containing isoleucine.
Humans need isoleucine, and reducing an essential nutrient too far could cause problems. Protein needs also differ with age, health, pregnancy, physical activity and other factors.
Older adults, for example, need adequate protein to help preserve muscle and strength. Any future advice about lowering a specific amino acid would therefore need to balance possible metabolic benefits against the risk of inadequate nutrition.
The study nevertheless provides an important clue about aging. Nutrition may influence health not only through total calories, fat or carbohydrates, but also through the precise mixture of amino acids contained in dietary protein.
Future research will need to determine whether moderate isoleucine reduction produces similar metabolic effects in people. Scientists may also investigate medicines that influence the body’s response to isoleucine without requiring highly restrictive diets.
For now, the research is best viewed as an intriguing laboratory finding rather than a new diet recommendation. It shows that a relatively small change in nutrient composition can have large effects in mice, but whether those effects translate safely to humans remains unknown.
The study adds to growing evidence that the biology of aging is closely connected with how the body senses and processes nutrients. Understanding those connections may eventually help scientists design diets or treatments that support healthier aging without depriving the body of nutrients it still needs.
If you care about wellness, please read studies about nutrients that could combat inflammation in older people, and essential foods for healthy aging.
For more health information, please see recent studies about the link between processed foods and chronic diseases, and a simple diet change for a healthier life after 65.
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