Bitter tastes may well be the key to a solution for the growing obesity epidemic. Administering a bitter substance to the stomach does initially stimulate the appetite, but then leads to faster satiation, doctoral research at KU Leuven has demonstrated.
For her doctorate in Medicine, Sara Janssen investigated the working of ghrelin, the so-called hunger hormone, which is produced in the stomach and has an effect on food-intake through interaction with the hypothalamus. It is due to this hormone that we get hungry. Ghrelin levels increase before meals and decrease after we have eaten. Sara Janssen: “The extent to which ghrelin decreases depends on what exactly we have eaten – sugar, fat, proteins, etc. In my doctoral research, conducted at the Targid Lab under the direction of Professor Inge Depoortere, I wanted to research whether ghrelin-producing cells in the stomach detect certain nutrients via taste receptors. To this end, we administered one particular taste – a combination of five different bitter flavours – directly into the stomachs of mice in order to measure the effect on ghrelin secretion.
“We initially observed that the amount of ghrelin increased and that the mice ate more. After half an hour, however, we observed a drop in food-intake and delayed gastric emptying, resulting in accelerated satiation.”
“In order to determine whether it was actually ghrelin that played a role in this process, we repeated the experiment with mice in which the ghrelin receptors had been deactivated by genetic manipulation and in which the taste receptors did not function as well. We observed that in these ‘knock-out’ mice, the increase of food-intake was blocked, but that the subsequent decreased food-intake and delayed gastric emptying was not.”
“We thus concluded that ghrelin does not affect the latter. The bitter substance appears to have a direct effect on the contraction of the gastrointestinal tract: the peristaltic movement is immobilised, as a result of which the emptying is delayed and a feeling of satiation follows. How this occurs, and via which receptors or ion canals, is still anyone’s guess, but in the long-term, this discovery may well be useful in the treatment of obesity.”
For this reason, a study has already been conducted in healthy volunteers, directed by Professor Jan Tack. Janssen: “We observed the same effect: administering a bitter substance directly into the stomach resulted in much faster satiation. This, of course, opens new perspectives. The Italian habit of drinking amaro – a bitter aperitif – before meals is thus not such a bad idea: bitters stimulate the appetite by releasing ghrelin, but also protect us against overeating. In the treatment of obesity, one might exchange the bitter aperitif with a so-called ‘bitter pill’, but that is something for the future.”