The protein shakes that health supplement stores sell, which people sometimes buy as a dietary aid to build muscle mass, may not actually be safe for health in the long run according to a new study in mice.
Many fitness protein powders that are commercially available consist primarily of whey proteins, which contain high levels of branched-chain amino acids (BCAAs).
Statistical reports show that in 2017 alone, the global whey protein market had a financial value of about $9.4 billion, with estimates suggesting that this may rise to around $14.5 billion by 2023.
BCAAs, which are three essential amino acids called leucine, valine, and isoleucine, are meant to help increase muscle mass in people who are interested in bodybuilding, though some scientists believe this claim to be "unwarranted."
Now, research in mice goes even further, suggesting that a diet that is high in BCCA-containing protein but relatively low in other essential nutrients can have many negative effects on long-term health and lifespan.
The investigators, who hail from the University of Sydney in Australia, have found that consuming excessively high levels of BCAAs may have adverse effects on mood, lead to food cravings and weight gain, and even shorten an individual's lifespan.
This research, the findings of which appear in the journal Nature Metabolism, stems in part from previous studies that co-lead author Samantha Solon-Biet, Ph.D., conducted.
"While diets high in protein and low in carbohydrates were shown to be beneficial for reproductive function, they had detrimental effects for health in mid-late life and also led to a shortened lifespan," says Solon-Biet.
"What this new research has shown is that amino acid balance is important — it's best to vary sources of protein to ensure you're getting the best amino acid balance."
Samantha Solon-Biet, Ph.D.
The researchers tested the effects of a high-BCAA diet in mice that would typically eat feed high in carbohydrates and low in fats.
They found that rodents who ingested a lot of BCAAs had high levels of these amino acids in their blood. Here, these amino acids affected the function of tryptophan, an alpha-amino acid from which serotonin, a key hormone and neurotransmitter, later derives.
"Supplementation of BCAAs resulted in high levels of BCAAs in the blood, which competed with tryptophan for transport into the brain," observes co-lead author Prof. Stephen Simpson.
"Tryptophan," he explains, "is the sole precursor for the hormone serotonin, which is often called the 'happiness chemical' for its mood-enhancing effects and its role in promoting sleep. But, serotonin does more than this, and therein lay the problem."
The researchers found that the competition between BCAAs and tryptophan in the blood led to lower-than-normal serotonin levels in the brain, which had unwanted consequences.
"This then lowered serotonin levels in the brain, which in turn was a potent signal to increase appetite," says Prof. Simpson, adding, "The serotonin decrease caused by excess BCAA intake led to massive overeating in our mice, which became hugely obese and lived shorter lives."
The researchers saw these ill effects in a group of mice that they fed double the usual amount of BCAAs for their entire lives.
For this reason, dietitian and public health nutritionist Rosilene Ribeiro, who is from the School of Life and Environmental Sciences at the University of Sydney and was not involved in the current research, advises that people should aim to balance out different protein sources in their daily diet to avoid undesired consequences for their health.
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