We’ve always thought that our feelings of hunger stem from an empty stomach but, recent research shows that it is in fact the presence of fatty foods in our stomach that results in the hunger sensation. Ghrelin is the so-called “hunger hormone” that is involved in this process. It also stimulates the uptake of nutrients and facilitates the storage of fat in the body.
However, ghrelin does not function by itself; it needs to be activated. For this to happen, it must be combined with a fatty acid. There is a specific enzyme called ghrelin O-acyl transferase, or GOAT, which enables the fatty acid to be added to the hormone in a process called acylation.
High concentrations of ghrelin are found in the body prior to meals and after eating the levels decline. For over a decade the thinking has been that ghrelin accumulates during the periods when we are not eating and that the fatty acids which are required for the activation of the hormone were produced by the body during this time as well. Now, according to research published in the June 5, 2009 edition of the journal Nature Medicine, it seems that this is not the case.
Hunger Hormone Is Activated By Fats In The Food We Eat
Recent research at the University of Cincinnati (UC) led by Mattias Tschöp, MD, UC associate professor of psychiatry and internal medicine, indicates that the fatty acids used in the acylation process are actually obtained directly from the food that we eat and are not produced by our bodies. It seems that once our system becomes aware of the presence of fats in the stomach, it notifies the brain, thereby triggering the metabolic processes necessary for the uptake of food and the storage of fat.
The research team used mouse models to determine the effects of increasing or eliminating GOAT. They found that, when on a diet with a high fat content, mice with increased levels of GOAT gained more fat than normal mice and those that had no GOAT stored less fat than normal mice. This indicates the relationship between GOAT and ingested fats.
Tschöp’s team only carried out animal trials and the results currently cannot be inferred in humans; however, there have been human studies at the University of Virginia which support the latest theory. In these trials it was found that, when fasting, active ghrelin levels were flat but, once foods containing fat were ingested, the ghrelin levels rose significantly.
Tschöp is keen to undertake further research on this finding. In particular, he wants to investigate it in the context of gastric bypass surgery. This is a successful procedure that is used to combat obesity and involves causing food to bypass the stomach and, incidentally, the regions of the digestive tract where GOAT and ghrelin are active. This means that the ghrelin is not activated and hence fat is not stored. Furthermore, one of the common effects of this surgery is reduction in appetite and improved metabolism. The new ghrelin-theory certainly makes sense in light of this operation and GOAT is an enzyme to be investigated for the treatment of metabolic diseases.