Overeating is a common problem in the U.S. that plays a significant role in the buildup of excess body weight and the onset of obesity. Researchers now know that consumption of certain foods stimulates pleasure centers inside the brain and makes food overindulgence more likely. According to a Yale University animal study published in 2012, the brain cells involved in overeating are the same as the brain cells accessed by cocaine and other drugs of abuse. Interestingly, people who overeat may have lower risks for abusing these drugs than people with little interest in food.
The Reward Pathway
The reward pathway is a collection of structures and chemicals in your brain that reinforces basic survival-related instincts such as eating and mating. When you engage in these instinctive activities, the reward pathway switches on and fills you with feelings of pleasure or well-being. The structures responsible for these feelings – including the hypothalamus, hippocampus, and amygdala – belong to an area of your mid-brain known as the limbic system. The chemicals that allow communication between the individual cells in these structures are known collectively as neurotransmitters.
You feel hungry when certain cells inside your brain’s hypothalamus grow active in response to a lack of adequate nutrients in your system. When you eat, these cells release a neurotransmitter called dopamine, which sends signals to other portions of your brain and helps create pleasurable sensations inside your body. While any consumption of food by a hungry person will activate the reward pathway to a certain degree, consumption of fatty or sweet foods has a particularly forceful effect on this pathway, and therefore triggers especially strong feelings of pleasure. For this reason, people who consume significant amounts of these foods can develop a tendency to overeat. Unfortunately, fatty and sweet foods often contain high amounts of calories, so people who eat too much of them also tend to gain weight.
Links Between Overeating and Drug Abuse
In the 2012 Yale study published in Nature Neuroscience, researchers examined the hypothalamus function of groups of mice. They discovered that the same cells in the hypothalamus that get activated by food consumption also get activated by drugs of abuse such as cocaine. In effect, these drugs have chemical structures that allow them to hijack the cells in question and trigger the reward pathway, even though no food has entered the body.
Mice in the study that had a strong interest in eating typically had relatively little interest in cocaine or other drugs, while mice in the study that showed less interest in eating typically had a relatively strong interest in these drugs. While care must be taken when applying the results of animal studies to human beings, these results may mean that people with low appetites may have higher risks for drug addiction that people with higher appetite levels.
The Development of Addiction
Inside your brain, drug abuse alters the normal output of dopamine and other important neurotransmitters. Cocaine and methamphetamine, in particular, trigger an excessive production of dopamine and/or stop your brain from removing dopamine from circulation and recycling it for future situations. Over time, your brain finds ways to offset the heightened presence of dopamine and establish a “new normal” in the reward pathway. This means that any given dose of drugs will eventually have a less potent effect. Addiction sets in when the user tries to recreate the initial rush of drug-related euphoria – and, unknowingly, boost dopamine output – by taking in higher amounts of the drug in question.
Some scientists believe that overeaters who consume lots of high-sugar or high-fat foods produce a similar situation in their brains by altering the ways in which their reward pathways responds to these foods. For instance, in another experiment on mice performed at the University of Pennsylvania, obese animals raised on a high-fat diet gradually became less responsive to the pleasurable effects of that diet over time. In order to get the same amount of pleasure as normal-weight mice, they had to significantly increase their intake of fatty foods. In essence, these mice became “addicted” to a higher level of fat intake.
Still, researchers at both Yale University and the University of Pennsylvania urge caution when making direct comparisons between drug addiction and overeating or food addiction. While mice are commonly used in a laboratory setting as stand-ins for the study of potential problems in human beings, results in mice don’t necessarily reflect conditions inside people. Additionally, addiction is a complex issue, and many separate factors can play a role in addiction-related issues for any given individual.