Lindy Valdez
Protein-rich diets are considered perfect – on the one hand for losing weight, on the other hand for staying healthy or getting healthy. However, studies have long pointed to the opposite: Those who eat less protein are healthier and live longer.
Less protein improves health
Carbohydrates and fats have a relatively bad reputation. Proteins, on the other hand, are considered valuable nutrients that fill you up, help build muscle, and help you lose weight. And while there are also studies linking low-protein diets to frailty and muscle loss in old age, more and more research is being published showing the opposite, particularly for younger and middle-aged people, namely that low-protein diets contribute to better health and also extended life expectancy. High-protein diets, on the other hand, can promote obesity, insulin resistance, and diabetes and shorten lifespan.
In 2014, an Australian study (promoting muscle growth) was published that looked at how different diets affected mice and their metabolism. When Dudley Lamming, a metabolism researcher at the University of Wisconsin, read the study, one result, in particular, fascinated him: it had been shown that mice whose diet contained the least protein were the healthiest.
BCAA’s are the problem
Since then, Lamming and his students have tried to answer the question of why a low-protein diet makes animals healthier. He found – not only in mice but also in humans – that diets that were particularly high in BCAA levels were associated with diabetes, obesity, and other metabolic diseases, while diets that had only low BCAA levels counteracted metabolic diseases and even extended the life expectancy of mice.
BCAA are the branched-chain amino acids leucine, isoleucine, and valine (BCAA for Branched Chain Amino Acids). They are among the essential amino acids, so they must be ingested with food. Especially in weight training, dietary supplements with isolated BCAAs are popular because they hope to build muscle better or prevent muscle breakdown.
In the summer of 2016, Lamming’s team published a randomized clinical trial on the subject, which showed that a low-protein diet improved metabolic health in humans in a manner similar to that in mice.
The overweight participants (with a BMI of around 30) consumed 7 to 9 percent of their energy requirements in the form of protein in the low-protein group, and 50 percent more protein in the normal-protein control group.
After 43 days, participants in the protein-restricted group had lost approximately 2.6 kg, specifically fat mass. Fasting blood sugar levels were lower, while levels of the hormone FGF21 had doubled. FGF21 sensitizes cells to insulin, reducing food intake and promoting fat burning.
In the control group with normal protein consumption, the FGF21 did not change. There was also no weight loss or other improvements in metabolic values.
When the levels of the individual amino acids in the blood were checked in the group eating reduced protein, it was found that the values of BCAA had mainly fallen, while all other essential amino acids (apart from lysine) were still strongly represented. So it seems that the declining BCAA levels in particular are what led to the health benefits.
BCAA reduction accelerates metabolism
Limiting BCAA consumption optimizes blood sugar levels and accelerates metabolism. A low-protein diet can increase metabolism even when consuming the same or more calories than a high-protein diet, says Dudley Lamming.
Protein restriction brings the benefits of eating less
Many people already know that eating less is healthy (calorie restriction), but that protein restriction, i.e. limiting protein consumption, is also healthy is something that is written much less about it. However, the scientific evidence on the benefits of both calorie restriction and protein restriction goes back almost a hundred years, and of course, there has been a lot of research on these topics, especially in recent years.
For example, in 2009, researchers showed that rhesus monkeys got sick later (related to age) and lived longer when fed a calorie-restricted diet. Studies with other animals showed very similar results.
It is now believed that many of the benefits of calorie restriction could be obtained more simply by simply reducing protein intake. In the corresponding animal studies, the desired health benefits were maintained even when the animals could eat as much as they wanted while consuming as little protein as possible.
BCAA reduction delays aging and prolong the life
Lamming and colleagues have now investigated in various studies how restricting BCAA intake alone would affect it. In January 2021, the summary of the results was published in Nature Aging. The researchers wrote, among other things, that the beneficial effects on metabolism from a protein-reduced diet could also be observed if one only reduced the amount of BCAA consumed.
With a BCAA-reduced diet, the aging process in the mice was delayed, their body composition improved (less fat mass) and their metabolic health (e.g. glucose tolerance) was optimized – even if they only started with the BCAA-reduced diet started. If the animals were fed the BCAA-reduced diet from birth and for life, their lives (especially in the male animals) could be extended by 30 percent.
BCAA reduced means that the amount of BCAA in the diet has been reduced by one-third. However, it was not a calorie-restricted diet because the animals could eat as much as they wanted.
BCAA inhibits the life-prolonging effect of undereating
Another study showed how strong the unfavorable effect of BCAAs or essential amino acids can be: rodents were given an extra portion of essential amino acids with a 40 percent calorie-reduced diet. This supplement blocked the longevity benefits of the calorie-restricted diet. The supplemented amino acids could thus inhibit the life-prolonging effects of eating less.
The higher the BCAA blood levels and the higher the BCAA content in food, the higher the risk of insulin resistance and obesity – in humans and animals, as various studies from the last decade have shown.
Methionine reduction also has a life-prolonging effect
In the fruit fly, which is often used as a study animal because there are more similarities between it and humans than one would assume, the reduction in the amino acid methionine, in particular, led to a longer lifespan.
In mice, a methionine-reduced diet also extended lifespan, slowed down the aging process of the immune system and the lens of the eye, and had a positive effect on blood sugar levels, thyroid hormones, insulin levels, and IGF-I levels. The latter was lower in methionine-poor animals (a high IGF-I level promotes the development of cancer, among other things). The liver was also significantly stronger in these animals, meaning it was less susceptible to oxidative stress from toxins.
A lifelong methionine-restricted diet extends the lifespan of rats by 30 percent. Methionine-reduced means that the diet contains only 0.17 percent methionine instead of 0.86 percent methionine. You can read which foods contain a lot of methionine in our article about the advantages of a methionine-reduced diet in autoimmune diseases.
How BCAAs can harm your health
The mechanism of how and why BCAAs have such a negative impact on health and lifespan is explained as follows: BCAAs increase the activity of mTORC1 in the muscles. mTORC1 is an enzyme with metabolism-regulating properties.
mTORC1 is also overactive in cancer. In cancer, mTORC1 helps the tumor grow and spread, which is why some cancer drugs have been developed to inhibit mTORC1. mTORC1 also increases insulin resistance, thus promoting diabetes and other age-related diseases (if the enzyme is too active), and is therefore associated with a shortened lifespan. If BCAAs now activate mTORC1, it becomes clear why a protein-rich or BCAA-rich diet has a negative effect on health and life expectancy.
Faster metabolism due to less BCAA
In April 2021, the scientists published another paper. In it, they examined whether the individual BCAAs had different effects on the mechanism explained above. Isoleucine had the strongest effect. The effects of valine were similar, albeit slightly weaker. Reducing these two amino acids in the diet had advantages for the respective animals. However, if the third BCAA (leucine) was reduced, this measure showed no advantage. On the contrary, it was rather harmful.
If mice that had become overweight due to a typical Western diet were given a diet low in isoleucine, the animals ate even more than before, but still lost weight. The metabolism had accelerated—in contrast to the metabolism in the calorie-restricted diet—which meant that the animals produced more energy in the form of heat even at rest.
