What? Obesity Is a Disease of the Brain?

We are in the midst of a great deal of cognitive dissonance about obesity. Part of the boilerplate description is that it is simply a dietary disease. But recent scientific and therapeutic advances tell a different story – that obesity is just as much a disease of altered brain function as it is a dietary problem.

A new study in Nature Metabolism – small and carefully conducted – is reminding people of this fact. Thus, it’s stirring up cognitive dissonance for people who can’t let go of thinking obesity is all about diet.

A Randomized Crossover Study

Mireille Serlie and colleagues conducted a sophisticated study of the brain responses to sugar and fat administered by a feeding tube. This was all about the neurologic effect of nutrients – not the experience of consuming them as food in a meal. They measured the responses to fat, sugar, and water in 30 persons with obesity and also in a group of 30 persons with a healthy body weight. They wrote:

“Participants with obesity have severely impaired brain responses to post-ingestive nutrients. Importantly, the impaired neuronal responses are not restored after diet-induced weight loss. Impaired neuronal responses to nutritional signals may contribute to overeating and obesity, and ongoing resistance to post-ingestive nutrient signals after significant weight loss may in part explain the high rate of weight regain after successful weight loss.”

Interesting, Though Small and Observational

We must remember that every study has its limitations. This study is certainly careful and sophisticated in its methods. But it is small and, in some respects, only observational. In fact, the researchers may not have made the necessary comparisons between groups to support such strong claims as they’re making. It might be that in the disease of obesity, people have alterations in brain function that interfere with signals of satiety. But evidence from this study has some issues.

In the light of evidence that new obesity drugs help with brain signaling for satiety and it makes sense when those new drugs work well. Losing weight with dietary changes did not improve the brain responses of people with obesity in this study.

Does Obesity Impair Brain Responses?

The observation these researchers could not find a measurable brain response to fat or sugar in people with obesity does not tell us why. But it does line up with other evidence suggesting that obesity may cause changes in brain function. Sadaf Farooqi, a researcher who was not involved with this study, explains:

“The study is very rigorous and quite comprehensive. The way they’ve designed their study gives more confidence in the findings, adding to prior research that also found obesity causes some changes in the brain,

“Are there changes that occurred in people as they gained weight? Or are there things that they were eating as they were gaining weight, such as ultra-processed foods, that caused a change in the brain? All of these are possible, and we don’t really know which it is.”

Whatever the causes of any changes in brain function, it is now becoming clearer that obesity may be a disease of altered brain signaling. This would explain why simplistic reliance on dietary changes to reverse it has yielded so little.

Click here for the new study in Nature Metabolism, here for a linked commentary, here, here, and here for further perspective.

Brain in a Jar, photograph by Gaetan Lee, licensed under CC BY 2.0

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June 13, 2023