APPETITE HORMONES

Hormones and Appetite 

There are numerous hormones in the body which serve to regulate appetite (the feeling of hunger) and satiety (the feeling of “fullness”), to either promote or inhibit eating (1). The release of these hormones is stimulated in response to anticipation of a meal and the digestion and absorption of food or drink (2).

A specific part of the brain called the hypothalamus serves as a control centre for hunger and satiety. The two primary hormones which influence appetite in an opposing manner are Leptin and Ghrelin (1).

Leptin

Leptin, otherwise known as the “satiety” hormone, is a hormone produced predominantly by fat cells and the small intestine (3). This sends a signal to the brain following a meal and works to suppress hunger when you have enough energy stored in the body (4). Ultimately, leptin plays a key role in regulating energy intake (and also expenditure), and therefore weight gain or loss (i.e. how much fat is stored in your body)(5). Given that leptin is made by fat cells, leptin levels are decreased in someone with a low amount of body fat, and conversely, are increased in someone who is overweight or obese (6). 

Of the two hormones, leptin seems to more greatly influence our energy balance and therefore weight gain. Leptin ultimately functions in the body to decrease appetite and increase energy expenditure to indicate that the body already has sufficient energy stores (i.e. body fat) in order to prevent excessive body fat gain (7). However, while many overweight/obese individuals have greater levels of leptin, they don’t respond as well to its signalling to the brain and develop a resistance to its appetite-suppressing effects (8).

Ghrelin

Ghrelin, otherwise known as the “hunger” hormone, on the other hand, is a hormone predominantly produced in the stomach and signals the brain to increase hunger and therefore food intake (9). Ghrelin levels will generally be increased in a person who is not eating enough and decreased in someone who is overeating. This is reflected in findings which showed that ghrelin production increased in children with anorexia nervosa and decreased in obese children (10, 11).

Ghrelin plays an important role in the initiation of a meal and also determines how fast hunger returns following a meal (12, 13). Typically, ghrelin levels increase dramatically in anticipation of a meal; this signals hunger, and then return back to normal around 3 hours following a meal (12, 13).

A study which involved ghrelin being administered to both obese and lean people resulted in an increase in overall food intake (14). Ghrelin may also influence energy balance and therefore body weight by promoting adipogenesis (which is essentially fat storage in the body) (15). Ghrelin levels are generally reflective of one’s nutritional intake, hence amount of body fat. Unlike Leptin, ghrelin levels are inversely correlated with body fatness, meaning they’re low in overweight/obese people and higher in lean people (16).

References

  1. Austin, J. and Marks, D. (2009). Hormonal Regulators of Appetite. International Journal of Pediatric Endocrinology, 2009, pp.1-9.
  2. Chaudhri, O., Wynne, K. and Bloom, S. (2008). Can Gut Hormones Control Appetite and Prevent Obesity?. Diabetes Care, 31(Supplement 2), pp.S284-S289.
  3. Margetic, S., Gazzola, C., Pegg, G. and Hill, R. (2002). Leptin: a review of its peripheral actions and interactions. International Journal of Obesity, 26(11), pp.1407-1433.
  4. Allison, M. and Myers, M. (2014). 20 YEARS OF LEPTIN: Connecting leptin signaling to biological function. Journal of Endocrinology, 223(1), pp.T25-T35.
  5. Friedman, J. and Halaas, J. (1998). Leptin and the regulation of body weight in mammals. Nature, 395(6704), pp.763-770.
  6. Considine, R., Sinha, M., Heiman, M., Kriauciunas, A., Stephens, T., Nyce, M., Ohannesian, J., Marco, C., McKee, L., Bauer, T. and Caro, J. (1996). Serum Immunoreactive-Leptin Concentrations in Normal-Weight and Obese Humans. New England Journal of Medicine, 334(5), pp.292-295.
  7. Campfield, L., Smith, F., Guisez, Y., Devos, R. and Burn, P. (1995). Recombinant mouse OB protein: evidence for a peripheral signal linking adiposity and central neural networks. Science, 269(5223), pp.546-549.
  8. Zelissen, P., Stenlof, K., Lean, M., Fogteloo, J., Keulen, E., Wilding, J., Finer, N., Rossner, S., Lawrence, E., Fletcher, C. and McCamish, M. (2005). Effect of three treatment schedules of recombinant methionyl human leptin on body weight in obese adults: a randomized, placebo-controlled trial. Diabetes, Obesity and Metabolism, 7(6), pp.755-761.
  9. Wren, A., Seal, L., Cohen, M., Brynes, A., Frost, G., Murphy, K., Dhillo, W., Ghatei, M. and Bloom, S. (2001). Ghrelin Enhances Appetite and Increases Food Intake in Humans. The Journal of Clinical Endocrinology & Metabolism, 86(12), pp.5992-5992.
  10. Shiiya, T., Nakazato, M., Mizuta, M., Date, Y., Mondal, M., Tanaka, M., Nozoe, S., Hosoda, H., Kangawa, K. and Matsukura, S. (2002). Plasma Ghrelin Levels in Lean and Obese Humans and the Effect of Glucose on Ghrelin Secretion. The Journal of Clinical Endocrinology & Metabolism, 87(1), pp.240-244.
  11. Tolle, V., Kadem, M., Bluet-Pajot, M., Frere, D., Foulon, C., Bossu, C., Dardennes, R., Mounier, C., Zizzari, P., Lang, F., Epelbaum, J. and Estour, B. (2003). Balance in Ghrelin and Leptin Plasma Levels in Anorexia Nervosa Patients and Constitutionally Thin Women. The Journal of Clinical Endocrinology & Metabolism, 88(1), pp.109-116.
  12. Cummings, D., Frayo, R., Marmonier, C., Aubert, R. and Chapelot, D. (2004). Plasma ghrelin levels and hunger scores in humans initiating meals voluntarily without time- and food-related cues. American Journal of Physiology-Endocrinology and Metabolism, 287(2), pp.E297-E304.
  13. Callahan, H., Cummings, D., Pepe, M., Breen, P., Matthys, C. and Weigle, D. (2004). Postprandial Suppression of Plasma Ghrelin Level Is Proportional to Ingested Caloric Load but Does Not Predict Intermeal Interval in Humans. The Journal of Clinical Endocrinology & Metabolism, 89(3), pp.1319-1324.
  14. Druce, M., Wren, A., Park, A., Milton, J., Patterson, M., Frost, G., Ghatei, M., Small, C. and Bloom, S. (2005). Ghrelin increases food intake in obese as well as lean subjects. International Journal of Obesity, 29(9), pp.1130-1136.
  15. Choi, K., Roh, S., Hong, Y., Shrestha, Y., Hishikawa, D., Chen, C., Kojima, M., Kangawa, K. and Sasaki, S. (2003). The Role of Ghrelin and Growth Hormone Secretagogues Receptor on Rat Adipogenesis. Endocrinology, 144(3), pp.754-759.
  16. Tschop, M., Weyer, C., Tataranni, P., Devanarayan, V., Ravussin, E. and Heiman, M. (2001). “Circulating Ghrelin Levels Are Decreased in Human Obesity.” Diabetes, 50(4), pp.707-709.

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