Study Shows Differences in Brain Response to Food in Overweight Individuals

The brains of people who are seriously overweight react differently to a full stomach than the brains of people with a healthy weight, say researchers at the AmsterdamUMC. “This is in line with stories of patients who feel that they have eaten insufficiently and therefore eat more than they need,” says researcher and professor of internal medicine Mireille Serlie of AmsterdamUMC.

In the Netherlands has 15 percent of adults severe overweight (obesity). “Our study shows that they have a communication disorder between the gastrointestinal tract and the brain,” says Serlie. “They are often accused of lacking discipline, but we are beginning to understand why losing weight can be so difficult.”

At the research 60 subjects participated. Half had a healthy weight, the other half obese (a BMI over 30). In a series of experiments, participants were fed nutrients into their stomach through a tube through their nose: glucose (sugar) or fat, or tap water as a control experiment.

Using two types of brain scans, the scientists looked at what happened in a number of brain areas after the stomachs of the test subjects had been filled with one of the three fluids.

After subjects with a healthy weight were given sugar or fat in the stomach, on average, brain activity changed in areas that the researchers know control appetite and food intake. Extra dopamine was also released, a signaling substance that gives us a good feeling and is important for healthy eating behaviour.

“In people with obesity, the researchers saw no measurable change in activity in the brain areas related to eating,” says Serlie. “So the brain did not register that there was food in the stomach. We also saw no extra dopamine being released after fat ended up in the stomach. This remained the case in people who went into the scanner again after they had lost 10 percent of their weight .”

Why these people ate too much despite the absence of the rewarding dopamine has not been investigated. “But obese people may need to eat more to produce dopamine.”

“This is really interesting and high-quality research,” responds professor of obesity Liesbeth van Rossum of Erasmus MC. “It shows that people with obesity cannot rely on themselves when it comes to whether they are full or not. We already knew that guidance and care are important for this group, but this research underscores this.”

According to Van Rossum, it was already known that obese people on average produce more hunger hormones and fewer satiety hormones on average, so they eat more easily. “This is yet another new way that too much belly fat has reprogrammed the body.”

Nutrition researcher Paul Smeets of Wageningen University is more critical. “The number of participants is small and you cannot translate this study to everyone with obesity. It also shows that there are significant differences in how their brains respond within the group of obese people, just like within the group with a healthy weight. “

According to Smeets, the study does underline that it is not easy to lose weight, because the body needs time to adapt to a new situation with a healthier weight.

The research also raises new questions. For example, Serlie wants to know when the brain changes. “Everyone overeats sometimes, but we think that the brain changes at some point and then you don’t get back to your normal weight.”