In the 1990s, obesity was characterized as a behavior disorder; individuals were thought to lack self-control when eating. Opinions changed when researcher Douglas Coleman at the Jackson Laboratory in Bar Harbor, Maine and Jeffrey Friedman of Rockefeller University experimented with two strains of mice that were genetically prone to obesity and diabetes. The researchers discovered that the obese mice lacked the hormone leptin, which suppresses appetite. The hormones leptin and insulin are secreted in the hypothalamus after a meal to suppress appetite. An imbalance of hormones could contribute to overeating, but obese people generally have a high level of these appetite-suppressing hormones, so the notion that obesity is solely a hormone disorder may be flawed because its causes are far more complicated. According to recent brain research presented in Scientific American, “obesity is driven by an overpowering motivation to satisfy the reward centers — the pleasure centers — of the brain.” Scientists commonly use the term “hedonic impact” to describe the conscious and unconscious pleasures that we receive.
During periods of hunger, hormones make food-related circuits more reactive, particularly those in the striatum, an area of the brain involved in many cognitive processes. The striatum contains pleasure-enhancing chemicals called endorphins. When we eat, our stomach releases appetite-suppressing hormones that hinder the release of endorphins from the striatum. As a result, we feel less hungry. However, the mechanism of appetite-regulating hormones does not always work, which is why even after consuming a big meal, people somehow find extra space in their stomachs to eat dessert.
Mouth-watering foods filled with sugar and fat bypass our appetite-regulating hormones by activating the reward circuits in the brain. The foods activate reward circuits faster than leptin can modulate the circuits. The foods also stimulate the release of dopamine, which passes by the striatum and flows into the prefrontal cortex, where decisions are influenced.
The high level of carbohydrates in the body triggers the release of the hormone insulin. In response, fat cells store excess fat. As insulin levels increase, weight gain occurs. Yet, the high concentration of hormones becomes less effective as the body becomes more tolerant towards food. Brain-imaging research at Brookhaven National Laboratory and Oregon Research Institute reports that reward systems in the brains of obese individuals respond ineffectively to food. The inclination to satisfy those reward centers drives obesity. Those individuals may overeat just to satisfy their reward centers while leaner individuals can satisfy themselves with less food.
Some experts believe that obesity and addiction should receive treatment in the same manner, but food and addiction are two different issues. Research provides evidence that the combination of fats and sugars maximizes food’s hedonic impact, rather than just one ingredient. Other experts argue that categorizing obesity as an addiction is unreasonable because people are all naturally inclined to food; otherwise, they would not survive. This categorization may or may not be useful, and scientists must look for a model that helps improve treatment methods.