Weight homeostasis (“the tendency towards a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes):
When you consider how much variation there is from day to day in the amount and types of food that we eat and the physical activity that we do, our body weight in adulthood remains remarkably stable over time. This indicates that somehow our cumulative energy intake and expenditure are matched (i.e. what we take in with food and what we expend with exertion/exercise is in balance).
The homeostatic regulation of body weight occurs primarily in the hypothalamus, through integration the homeostatic regulation of body weight occurs primarily in the hypothalamus, through integration of signals from the periphery which convey information about both short-term food intake and long-term energy stores. This involves a complex interplay between various hormones in the body.
The hormones leptin and insulin are involved in long-term signalling, while short-term signals send information to the brain on a meal-to-meal basis, including hormones from the gastrointestinal tract and pancreas, like ghrelin, from the stomach, which increases hunger, cholecystokinin (CCK), GLP-1 (glucagon-like peptide-1), PYY (peptide YY) and amylin, among others.
Leptin is the key peripheral hormone involved in body weight regulation. It is secreted mainly by adipocytes (fat cells), in proportion to fat mass, and works by inhibiting food intake and increasing energy expenditure.
It should be mentioned here that homeostatic regulation is not the only factor affecting our feeding. Clearly if appetite were controlled only by homeostatic mechanisms, we wouldn’t derive the pleasure that we do from eating, and we would eat only to meet nutritional requirements. But in addition to homeostatic pathways, the hypothalamus receives input from the cortex and reward circuits in the limbic system – or hedonic pathways – related to the sight, smell and taste of food, along with emotional and social factors which all contribute to energy intake and expenditure. These hedonic pathways can override homeostasis, so sometimes we want to consume palatable, energy- dense food even when our energy stores are adequate.
In summary, body weight – or adiposity – is homeostatically regulated, and there also sustained physiological adaptations that counteract weight loss.
This means that people with obesity who have lost weight don’t regain it because they lack willpower or motivation; obesity is a chronic condition which is not cured by weight loss. In order to maintain weight loss, long-term treatment is required, including continued adherence to diet and physical activity changes, as well as a strategy to prevent weight regain.