Obesity is a serious, ongoing problem in America. According to figures released in 2012 by the Centers for Disease Control and Prevention, almost 36 percent of all U.S. adults carry enough extra weight to qualify as clinically obese, and obesity plays a known role in preventable forms of serious illnesses that include strokes, heart disease, type 2 diabetes, and specific forms of cancer. Some people claim that their eating patterns are motivated by a literal addiction to certain types of food. While it can be easy to dismiss these claims, current research indicates that they have some basis in scientific fact. The Links Between Food and Pleasure All functioning human brains contain chemicals called neurotransmitters, which relay vital signals and messages between individual nerve cells in specific brain areas. One of the main neurotransmitters is a substance called dopamine. When dopamine levels in your brain rise, their presence triggers heightened activity in a group of related brain structures collectively known as the limbic system. You rely on your limbic system for your everyday ability to experience pleasure, and to a certain extent, the more dopamine that becomes available in this system, the greater degree of pleasure you feel. On an evolutionary level, the limbic system rewards actions and behaviors that tend to support and sustain human life. Chief among these actions and behaviors is the act of eating. Differing Effects of Food Not all foods produce the same increases in dopamine and limbic system activity. On a basic survival level, the human body has a natural preference for calorie-rich foods, such as fats and sugars, which help sustain life even in harsh physical environments. Our collective survival-related heritage also gives us a strong preference for salt, which we require in certain amounts for the maintenance of proper internal fluid levels. As a result of these preferences, when you eat fatty, sugary or salty foods, you significantly boost your dopamine levels and trigger an elevated pleasure response in your limbic system. In addition, activation of your limbic system makes you more likely to eat lots of pleasure-giving food in a single sitting, and also more likely to desire this food again relatively soon after you finish any given meal. Food Addiction In addition to activating in the presence of behaviors that sustain life, the limbic system activates in the presence of any chemical that boosts your brain's dopamine levels, prevents the normal breakdown and recycling of dopamine inside your brain, or closely mimics the natural effects of dopamine or certain other neurotransmitters. The path toward classic drug addiction begins when certain chemicals, such as stimulants or opioids, enter the brain and trigger dopamine-related changes that increase limbic system activity. In 2011, researchers at Yale University reported the results of a study that examined similar addiction-like links between obesity and food-related responses in the limbic system. At the beginning of the study, these researchers used a survey called the Yale Food Addiction Scale to examine food-related attitudes in all study participants. Next, they used a brain imaging technology called fMRI (functional magnetic resonance imaging) to measure the participants' brain responses while drinking a chocolate milkshake, and also while drinking a glass of water. They also measured participants' brain responses while merely looking at pictures of a milkshake and pictures of a glass of water. According to the creators of the Yale Food Addiction Scale, high scores on the survey indicate the probable presence of a food addiction. Prior to 2011, no real-world testing had been done to prove or disprove this claim. However, the 2011 Yale study seems to confirm the accuracy of the addiction survey. Compared to study participants with low Addiction Scale scores, while drinking a milkshake, participants with high scores showed increased activity in parts of the brain associated with loss of normal behavioral control. While merely looking at pictures of a milkshake, these same participants also showed increased activity in parts of the brain that anticipate the start of a pleasurable event or activity. Trends and Considerations While no one knows for sure at this point, some people may have pre-existing susceptibilities to food addiction. In addition, certain trends in the food industry (including the presence of high amounts of fat, salt, and sugar in popular prepared foods) may help contribute to cases of food addiction by bringing out latent tendencies in susceptible individuals. In people who already exhibit food-addictive behaviors, consumption of these popular foods may also promote obesity by reinforcing the tendency toward poor nutritional choices. Interestingly, not all participants in the 2011 Yale study with high scores for food addiction were either obese or overweight. In some cases, high-scoring participants with healthy body weights may have genetic or behavioral traits that give them firmer control over their actions even when their bodies tell them to overeat. In other cases, these individuals may control their weight through means that include increased participation in exercise or participation in a more generally active lifestyle.