A group of brain cells control our appetite, "telling" our brains to refuse food.
But a team of researchers from the University of Warwick in Coventry, United Kingdom, have made a groundbreaking discovery that could transform dieting and weight loss practices.
The scientists - led by Nicholas Dale, a professor of neuroscience at the University of Warwick - found that a group of cells called tanycytes "communicate" with the brain directly to "tell" it to stop the sensation of hunger.
The first author of the new study is Greta Lazutkaite, and the findings were published in the journal Molecular Metabolism.
Tanycytes are non-neuronal, or glial, cells located in an area of the brain called the hypothalamus, and recent studies have suggested that these cells may control energy levels and bdy weight. But this is the first time that scientists show how these cells signal satiety by detecting certain nutrients in food.
More specifically, the authors explain, it was known that tanycytes are able to detect glucose in the cerebrospinal fluid, but the new research shows that essential amino acids can activate these cells and make us feel less hungry.
How tanycytes control appetite
Prof. Dale and team used calcium imaging to make the cells fluorescent and track them in vivo. They added several essential and nonessential amino acids to these brain cells.
Tanycytes responded to two essential amino acids - lysine and arginine - within 30 seconds, sending signals to other parts of the hypothalamus that control appetite.
After removing the genes that control the receptors responsible for detecting the umami taste in mice, the researchers found that tanycytes no longer responded to the amino acids.
This led them to believe that amino acids are detected by umami taste receptors, mediating the relationship between the amino acids and the brain cells. In humans, the umami taste refers to the savory taste of glutamate, and in rodents, it characterizes most non-aromatic amino acids.
Prof. Dale comments on the findings, saying, "Amino acid levels in blood and brain following a meal are a very important signal that imparts the sensation of feeling full."
"Finding that tanycytes, located at the center of the brain region that controls body weight, directly sense amino acids has very significant implications for coming up with new ways to help people to control their body weight within healthy bounds."
Prof. Nicholas Dale
Findings help to 'overcome obesity epidemic'
According to the latest estimates, over a third of the U.S. population is obese, and between 15 and 20 percent of children and teenagers are affected.
But the new findings by Prof. Dale and team point to a new avenue for tackling the obesity crisis. By changing the content of our diets, we could activate tanycytes quicker, reach the feeling of satiety, and reduce food intake.
Lysine and arginine are found in abundance in meat and poultry but also in mackerel, plums, apricots, avocados, lentils, and almonds. Eating these foods could potentially make us feel full more quickly.
Furthermore, the authors suggest that the hypothalamic brain circuits responsible for appetite control could be changed with dietary interventions.
"Studies have demonstrated," they write, "that tanycytes can generate new neurons [...] meaning that the neuronal networks of the hypothalamus are highly plastic and can be remodeled by diet."
The authors conclude that overall, "A more detailed understanding of how food intake and energy expenditure are determined in the brain may lead to the development of new strategies for overcoming the obesity epidemic and other metabolic disorders."