Reward centers in the brains of some obese women continue to promote rewarding feelings associated with food, even after they are no longer hungry, a study published in Obesity says.
According to the National Institutes of Health, 1 in 3 adults has a body mass index (BMI) above 30, which medically classifies them as obese. Two in 3 adults have a BMI above 25, medically classifying them as overweight.
Concerns Associated with Obesity
Many individuals medically classified as overweight or obese according to the BMI scale may be at greater risk for type 2 diabetes, cardiovascular problems such as high blood pressure and stroke, joint pain, sleep apnea, and some types of cancer. These concerns may also, in some cases, affect mental health and undermine quality of life.
People who are overweight frequently face discrimination and judgments about their bodies from people in their lives, medical professionals, and society as a whole. Prejudice and fat shaming may undermine self-esteem and can, for some, lead to the development of other health concerns, both mental and physical. Self-esteem issues may further contribute to obesity.
A study GoodTherapy.org covered in 2015 linked negative body image to obesity risk. (It may be worth noting, however, that many people who are overweight or obese experience no medical issues, mental health concerns, or emotional issues related to their weight—excepting the prejudice they are often likely to experience from other individuals.
How Do Brain Responses to Food Differ?
Researchers performed MRI scans on the brains of 30 women who had fasted for nine hours, before and after the women ate. Fifteen participants had a BMI under 25, which is considered by many medical professionals to indicate a “healthy” body weight. The other 15 participants had a BMI higher than 35 and were thus considered severely obese.
When hungry, all participants showed increased activity in the brain’s limbic cortices and neocortices and in the midbrain—regions that, according to previous research, may play a role in reward and motivation. After eating, brain activity in these regions decreased for lean women but remained high for obese women. Participants provided feedback about their levels of hunger and fullness after eating and looked at images of food. Lean women experienced a 15% drop in their interest in food images, but obese women were found to only experience a 4% drop.
These findings, the study’s authors say, suggest that some people may not feel as full after eating and that people may respond to food in different ways. The study did not explore the origin of this brain difference, so it is unclear whether obesity can cause brain changes or if characteristics in the brain (such as this difference) can have an impact on a person’s response to food.
The BMI as a Diagnostic Tool
BMI remains a controversial measure of health, as do terms such as “obese” and “overweight.” The Health at Every Size Movement has long pushed to abandon weight-based measures of health, citing research that people with larger bodies face intense discrimination, which can be a source of mental health concerns. Medical support for the notion of obesity may be used to back up prejudiced attitudes toward people with larger bodies.
A recent UCLA study found that 29% of people classified as obese were in good health, while 30% of people with “healthy” body weights had metabolic issues.
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- Khan, A. (2016, February 4). BMI mislabels 9 million Americans as ‘overweight’ or ‘obese,’ study says. Los Angeles Times. Retrieved from http://www.latimes.com/science/sciencenow/la-sci-sn-bmi-does-not-measure-health-20160204-story.html
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