There exists a highly complex negative feedback loop for appetite regulation. This feedback loop ensures that no overeating occurs and this helps maintain body weight within a set range. The hormones and nerve signals that regulate this feedback loop are highly complex and their interactivity is not fully understood. However, studies have identified a number of factors that are responsible for maintenance of this feedback loop, and nutritional studies have been particularly helpful in this regard. Many nutrients stimulate hormones and gut peptides that participate in appetite regulation and the metabolites of many nutrients can also stimulate the satiety signal to prevent overeating. Eating low quality foods absent of these essential factors may lead to overeating through an inability of the body to regulate its appetite effectively. One such group of compounds that appear to show particular appetite regulatory effects are the short chain fatty acids that are produced via the metabolism of dietary fibre by colonic microflora.
Gut bacteria can produce short chain fatty acids through fermentation of dietary fibre. One study investigated the effects of colonic propionate production on the reward pathways of the brain in response to food. Non-obese subjects were fed an inulin-propionate ester (fibre bonded to the short chain fatty acid propionate). This ester would be cleaved by gut bacteria to yield a source of propionate that would increase the propionate content of the colon. As levels of propionate increased in the subjects, changes in brain chemistry showed that the appeal of high energy foods was blunted in the subjects and this was reflected in a reduction in energy intake at an ad libitum meal. These changes were not associated with change in insulin or glucose levels in the blood. Therefore increasing the propionate content of the colon may be one mechanism by which appetite is regulated. Dietary fibre is able to increase colonic propionate production and high fibre diets are associated with weight loss.
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