The Effects of Obesity On the Brain May Impede Weight Loss

A recent study reveals that if people gain weight, their brains may stop responding to signals that help them feel satisfied after consuming particular nutrients.

A new study reveals that obesity may permanently impair the brain’s capacity to absorb signals that are meant to help people feel pleased and full after consuming foods high in sugar and fat.

When a person eats, the gut ordinarily sends signals to the brain alerting it to the presence of nutrients. Scientists believe this process may be essential for aiding in the regulation of eating behavior. However, in the recent study, which was published in the journal Nature Metabolism, researchers discovered that in obese individuals, the brain’s capacity to react to these signals is significantly reduced.


In order to compare the effects of two different types of nutrients on the brain in individuals with a body mass index (BMI) of 25 or less, which is considered a healthy weight, and in individuals with a BMI of 30 or more, which is considered obese, researchers wanted to directly assess how the brain reacts to carbohydrates and fats in these two groups of individuals. 

Feeding tubes were used to deliver sweets or fats directly into participants’ stomachs, and functional magnetic resonance imaging (fMRI) was used to look at how these nutrients affected the brain’s chemical reactions.

Infusions of carbohydrates and fats resulted in decreased activity in multiple brain areas related to appetite regulation among those with lower BMIs, the study discovered. But in obese persons, researchers found no evidence of a brain reaction to these nutrients.


This was unexpected, said Mireille Serlie, MD, PhD, a senior study author from the Yale School of Medicine in New Haven, Connecticut.

Dr. Serlie added, “We expected that responses between lean and obese people would differ, but we weren’t prepared for this absence of alterations in brain activity in obese people.


Even After Weight Loss, Brain Signals for Fullness and Satiety Didn’t Return

The obese participants were then instructed to stick to a weight loss plan for 12 weeks by researchers to determine whether it could be able to change this lack of brain reaction in obese individuals. However, the brain’s lack of reactivity to carbohydrates and fats persisted even in the sample of subjects who lost at least 10% of their body weight.

None of the reduced responses, according to Serlie, were regained.

One drawback of the study is that brain imaging was done within 30 minutes after participants had been given carbohydrates and fats. Due to the timeframe, it’s likely that the study missed any brain responses to these nutrients in obese individuals that were merely postponed and not fully eliminated.


The study’s restriction to participants aged 40 and older is another flaw, as younger people might have experienced different outcomes.


Lack of Brain Signaling Could Contribute to High Calorie Intake

However, Samuel Klein, MD, a professor and director of the Center for Human Nutrition at the Washington University School of Medicine in St. Louis, who wasn’t involved in the study, points out that one advantage of the study is that nutrients were directly infused into the stomach, avoiding the possibility that the brain responses would be influenced by how foods taste.

The excessive calorie intake that leads to obesity and weight gain following diet-induced weight loss, according to Dr. Klein’s findings, may be caused by changes in how the brain processes nutrients in obese individuals.

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