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Why Do People Overeat? Obesity epidemic has been a global hot issue. Health experts together with the government authorities around the world are finding all means to educate people not to overeat hoping to curb the growing rate of obesity. The reason is rather simple. Obesity is the cause of many medical disorders including heart disease, stroke, diabetes, high blood pressure, and even certain types of cancer. All these chronic diseases could incur huge medical expenses that can be a burden on the people themselves as well as the governments. But why people, especially those who are overweight or obese, still continue eating more than their bodies require, despite the numerous educational campaigns and efforts made by the authorities? Scientists at the Scripps Research Institute in Florida might have found the answer. In a paper published on March 28, 2010 in the journal “Nature Neuroscience”, they reported that the same molecular pathways that steer people into drug addiction also cause people to overeat, driving them into obesity. Their findings were based on the trials they performed on laboratory animals.
In the study, scientists divided the laboratory rats into 3 groups and examined their behaviors for 40 days. The first group was fed regular rat food and they were the control group. The second group was fed the so-called junk food including bacon, sausage and cheesecake for just 1 hour each day, while the third group was offered the similar junk food for up to 23 hours a day. The almost unlimited binging changed the brains of the rats in the third group. They ate twice as many calories as those in the control group and their size grew dramatically. When the scientists removed the junk food from the rats in the third group and tried to offer them nutritious diet, they simply refused to eat. In fact, they starved themselves for 2 weeks after stopping them from junk food. Meanwhile, an interesting scenario was also noted in the study. When electric shock was applied to the rats’ feet in the presence of food, the rats in the first 2 groups were frightened away from the food, but the electric shock did not scare away the obese rats in the third group. They were simply addicted to food and focused their attention solely on eating the food! Realizing that the obese rats were addicted, the scientists focused on a docking point, or receptor, on the surface of neurons that binds to a 'feel-good' brain chemical called dopamine. Dopamine is central to the reward system, and is commonly associated with the pleasure system of the brain, providing feelings of enjoyment and reinforcement to motivate a person to perform certain activities. Dopamine is released by pleasurable experiences such as sex, food and narcotics. Previous studies had already found that among cocaine users, the brain becomes flooded with dopamine and over stimulates the so-called dopamine 2 receptors (D2Rs). The overstimulation causes the body to adapt by decreasing the activity of the D2Rs. As a result, there is a progressively worsening 'reward response', or uptake of the pleasure-giving chemical in brain cells. Similar changes in the D2Rs were found in the food-addicted laboratory rats. Overeating caused the D2Rs level to in the brains of the obese rats to drop. Through monitoring of brain electrodes, the rats in the third group were found to develop a tolerance to the pleasure the food gave them and they had to eat more to get “high”. In other words, junk food elicits addictive response, which did not surprise the scientists at all. According to them, people have made their food very similar to cocaine nowadays.
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