You lean back from the dinner table, feeling like you physically couldn’t fit another bite in – but then someone offers pie and you just can’t say no. Scientists have now identified the neurons behind the “dessert stomach” phenomenon.
In a new study, scientists at the Max Planck Institute for Metabolism Research gave mice the option to eat sugary snacks after a meal. Unsurprisingly, they dug in even when they should have been feeling pretty full. So the team examined what was going on in their brains during this process.
That feeling of fullness you get after a big meal comes not just from your stomach but your brain. Specifically it’s the pro-opiomelanocortin (POMC) neurons in the hypothalamus, which activate after feeding to make sure you stop stuffing your face.
To the team’s surprise, the POMC neurons had a secret second gig. While firing off the “I’m full” signal, they also sent projections into a neighboring region of the brain, the paraventricular thalamus, releasing a hormone called β-endorphin. This opioid pathway switches on an appetite specifically tuned for sugar, even when the mouse merely perceives that there’s sugar around. Eating their dessert triggers a feeling of reward that keeps the mouse chowing down on sweets.
Intriguingly, the researchers found that this pleasure pathway was only activated by sugary foods. When they ate normal or fatty foods after a meal, it stayed silent.
“From an evolutionary perspective, this makes sense: sugar is rare in nature, but provides quick energy,” said Henning Fenselau, head of the study. “The brain is programmed to control the intake of sugar whenever it is available.”
Next, the researchers blocked the opioid pathway, and found that satiated mice were able to resist the allure of dessert. Stranger still, blocking the release of ß-endorphin didn’t stop hungry mice from consuming sugar.
To investigate whether a similar mechanism was at play in humans, the researchers fed volunteers a sugar solution – and found that the same region of the brain reacted to the substance. This suggests that blocking this pathway could be a new way to curb overeating and obesity.
“There are already drugs that block opiate receptors in the brain, but the weight loss is less than with appetite-suppressant injections,” said Fenselau. “We believe that a combination with them or with other therapies could be very useful. However, we need to investigate this further.”
Brain activity alone isn't the full picture, of course. Other studies have found that signals from your gut microbiome could influence why there always seems to be room for Christmas pud.
The research was published in the journal Science.
Source: Max Planck Institute
