‘Non-essential’ building block proves vital to a healthy protein diet

A ‘non-essential’ amino acid – so called because the body can make it from other nutrients – may act as a nutritional signal to guide the body’s responses to a low-protein diet, a RIKEN-led team has found. in a study of fruit fly larvae. If a similar control mechanism works in mammals, it may be possible to use it to control appetite.

To help us decide whether to eat another serving of beef or fish, our brains have developed mechanisms to detect changes in the building blocks of protein in the body and adjust the intake of protein-rich foods accordingly. . Researchers have long assumed that this process relies only on those building blocks, called amino acids, that the body cannot produce naturally on its own.

But now, a study led by RIKEN has found that’s not always the case. “We have discovered a new mechanism for sensing and adapting to dietary protein shortage,” says Fumiaki Obata of the RIKEN Center for Biosystems and Dynamics Research (BDR).

Known as tyrosine, the amino acid is found in dairy products, meats, nuts, beans, and other protein-rich foods. But the body can also synthesize tyrosine from another amino acid called phenylalanine, which is found similarly in plant and animal foods.

As Obata and his BDR colleague Hina Kosakamoto have now shown, flies slow their rate of protein metabolism and increase their food consumption when tyrosine levels in the diet are low, a sign of adaptation to scarcity. of proteins. But, conversely, when tyrosine is ingested in greater quantity, flies accelerate their protein metabolism. They also limit the intake of additional protein, ensuring that macronutrient levels stay within a healthy range.

The team identified several of the molecular players and signaling pathways involved in regulating the body’s response to tyrosine levels, although exactly how this occurs remains unclear. They ruled out a common mechanism by which the brain detects nutritional imbalances. But as Kosakamoto points out, “We still don’t know how tyrosine is detected in cells.”

Another research priority for the team is to corroborate the findings in mouse models. This will help determine the relevance of the findings for human physiology and medicine, as well as agriculture and animal husbandry. “If tyrosine plays a similar role in mammals, we could use tyrosine restriction to control appetite, treat metabolic syndrome, or even prevent aging,” Obata says. “Potentially, our knowledge could also be applied in the livestock industry to improve animal health and production.”

The study is published in Natural metabolism.