Food, Global Health

Separate gut-brain circuits for fat and sugar reinforcement combine to promote overeating

Food is a powerful natural reinforcer that guides feeding decisions. American and French scientists provide new insights into the complex sensory circuitry that mediates motivated behaviour towards fatty and sweet foods. Their findings suggest that because of separate and potentially additive neuron circuits, the combined consumption of fatty and salty foods can encourage people to eat more, thus impeding conscious efforts to diet.

Published on 12 March 2024

© INRAE

Although it is accepted that the vagus nerve transmits internal sensory signals from the gut to the brain, informing the latter of the nutritional value of the foods consumed, the cellular and molecular bases underlying the response of the reward circuit specific to macronutrients are poorly understood. The researchers wanted to determine whether the detection of fats and sugars by the vagus nerve are dissociated and the consequences of this at the level of the reward circuit.

Using imaging, the scientists examined in vivo the cellular mechanisms linked to the post-ingestion responses to fats and sugars, and showed that they activate spatially separate sub-groups of neurons in the vagus nerve.

Specific stimulation of these fibres made it possible to evaluate the role of each sensory pathway in motivated behaviour. Thus the separate post-ingestion detection of fats and sugars generates a release of dopamine in the striatum, which triggers a reward specific to each macronutrient. One notable finding was that the combined activation of these two circuits in the context of the extemporaneous ingestion of fatty and sweet foods exerted an additive effect, as proved by a much greater induced consumption, even with an equivalent calorie intake.

These findings throw new light on the complex sensory circuits that intervene in motivated behaviours relative to fatty and sweet foods. They are a reminder of the interactions between different nutrients and highlight the existence of complex physiological effects that may impede conscious efforts to adhere to a weight-loss diet.

This discovery opens new perspectives for our understanding of the mechanisms underlying excessive eating and obesity.

Reference: https://doi.org/10.1016/j.cmet.2023.12.014

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