In a new study from the University of Wisconsin, researchers found that low-protein diets can reprogram metabolism and reduce the risks of many chronic diseases.
They discovered a little-known but robust pattern across both animal models and humans.
Diets high in the three branched-chain amino acids, BCAAs, are linked to diabetes, obesity and other metabolic illnesses.
Conversely, diets low in BCAAs can counter these metabolic ailments and even extend the healthy lifespan of rodents.
It’s not yet entirely clear just how BCAAs control metabolism, although restricting them seems to encourage faster metabolisms and healthier blood sugar control.
And due to the immense complexity of diet-related research in humans, the full effects of BCAA restriction in people aren’t yet known.
Scientific evidence about the benefits of both calorie restriction and protein restriction extends back almost a century, and the field has grown in recent years.
There is evidence that many of the benefits of calorie restriction can be accomplished just by limiting protein intake. Those benefits persist even when animals eat as much as they want.
In the study, the team examined BCAAs, which make up three of the nine essential amino acids, which humans cannot make on their own and must eat.
They tested a diet in mice that contained just one-third the normal amount of BCAAs. It wasn’t a calorie-restricted diet; the animals could eat as much as they wanted.
Male mice who ate the diet their entire lives lived about 30% longer on average. It’s not clear why female mice didn’t seem to benefit, though other research suggests female mice may need a slightly different diet to see benefits from reduced BCAA consumption.
Male mice showed reduced activity of a biochemical pathway known as mTOR, which is activated by BCAAs. Many experiments have shown that treatments that reduce mTOR activity tend to improve metabolic health and increase longevity.
The team also asked if the three individual BCAAs—leucine, isoleucine, and valine—had unique effects on the body, or if they all acted similarly.
They found that isoleucine restriction has by far the most potent effect. Mice fed with low-isoleucine diets were leaner and demonstrated healthier blood sugar metabolism.
Valine-restricted diets had similar, but weaker, effects. Reducing levels of leucine had no benefit and may even be detrimental.
To study how the three BCAAs affected obesity, the researchers provided mice with a so-called Western diet, which is high in both fat and sugar. After a few months on a Western diet, mice grow obese.
When the team began feeding these obese mice a Western diet that was low in isoleucine, the mice began to eat more food but nonetheless lost weight.
The weight loss was primarily caused by a faster metabolism, where the body burns more calories as heat while resting.
Turning to human health, the team analyze the dietary diaries and weights of participants in the Survey of the Health of Wisconsin.
They discovered that an increased intake of isoleucine was linked to a higher body mass index.
A lot of modern diet advice recommends adding protein, not limiting it. Protein promotes a feeling of fullness, which can help people control their calories. And for athletes who are building and repairing muscle, these essential amino acids are, indeed, essential.
But with the majority of the U.S. population being overweight and sedentary, the team thinks there’s an opportunity to rethink diets.
Humans overall are not so good at long-term adherence to calorie-restricted diets. Yet evidence from animal models suggests that low-protein diets help shed fat even with normal caloric intake by reprogramming metabolism.
More nutritional research needs to be done, especially to create a low-isoleucine diet. And Americans typically eat far more protein than they need, so changing that habit might be hard.
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The study is published in Cell Metabolism. One author of the study is Dudley Lamming.
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