Scientists found a reason why diets are so hard to keep up: When food is lacking, some hungry brain cells start to devour themselves, sending out a hunger signal that prompts us to eat.
Molecular biologist Susmita Kaushik and her team at the Albert Einstein College of Medicine took mice, left them fasted for twelve hours and then examined how their brains reacted to the lack of food. Interestingly, Agouti-related peptide neurons (AgRP), cells playing an important role in hunger regulation, had started devouring themselves.
To a certain extent this process, called “autophagy”, always happens in the body, as it allows cells to rejuvenate themselves and get some of their energy. But here it may be related to the regulation of hunger and satiety.
Fat Makes You Hungry?
The trigger signal for the AgRP apparently are free fatty acids: When a person eats less than is needed to sustain weight, the body starts breaking down fat reserves for energy. The brain cells take up free fatty acids set off by this process, this sets off the autophagy, and, finally, the autophagy prompts the AgRP neuron to generate a hunger signal.
This could also explain a rather vicious circle: If free fatty acids are responsible for heightened feelings of hunger, then it is possible that a nutrition high in fats makes hunger worse. The more a person weighs, the more food high in energy has to be eaten to feel satiated, and the highest energy per gram comes from fat: 9 kcal. Carbohydrates and protein both carry less than half that, 4 kcal.
Blocking The Trigger
Another interesting aspect of the study was that when the AgRP autophagy was blocked, the mice apparently felt less hungry, ate less and lost weight.
However, so far this is still theoretical. The problem is to specifically block autophagy in those cells where we want it. Randy Seeley, neuroscientist and director of the Cincinnati Diabetes and Obesity Center told The Scientist:
There are a number of significant challenges. Perhaps the biggest is that autophagy is a cellular process that happens in dang near every cell. There is no way to control the process in only AgRP neurons.
Still, this could prove to be very interesting and may bring us one step closer to understanding the whole picture of hunger / satiety regulation.
Picture courtesy of “GreenFlames09“.