For most people, hunger is not the only factor that influences eating behaviors, and some have more difficulty regulating their food intake than others. Scientists have proposed the excessively sweet, salty, and/or fatty (“highly palatable”) foods common in the standard American diet can produce addiction-like effects in the human brain, driving loss of self-control, overeating, and weight gain. In fact, the behavioral and neurobiochemical characteristics of substance abuse and overeating are quite similar, and the idea of food addiction is becoming more widely accepted among scientists.
Dopamine is a brain chemical that is involved in motivation, pleasure and reward. The dopamine reward system has been shown to be involved in overeating behaviors in animals, and the effects are similar to those of drug dependence. Studies on brain activity in humans have provided preliminary evidence supporting the idea that overeating alters the dopamine reward system, which then acts to drive further overeating. Substance abuse is known to reduce the numbers of dopamine receptors (called D2 receptors) in the brain, and this is thought to underlie the tolerance associated with addiction — over time, greater amounts of the substance are required to reach the same level of reward because the reward response has been reduced. Similarly, in the context of food addiction, reduced numbers of dopamine D2 receptors have been reported in obese compared to lean humans, and the dopamine reward response becomes diminished over a period of weight gain. The dopamine reward response is also reduced among women with bulimia compared to healthy women. Frequent consumption of ice cream was shown to reduce the reward response in adolescents. Together, these studies imply that overeating results in a diminished dopamine reward response, resulting in a constant cycle of overeating and a progressively worsening addiction to low-nutrient, highly palatable foods.
