The Gut-Brain Axis: How Sugar & Fat Impact Our Brains

By Laura Tran, C2ST Intern, Rush University

What drives our insatiable cravings for sugary or fatty foods?

The culprit is both our gut and our brain.

Our gut is home to 500 million neurons, which are all connected to and communicate with our brain (1). One of the most prominent nerves is the vagus nerve. This nerve serves as an information highway between the gut and the brain, driving signals from the brain to the gut and vice versa (2). This is evident in how we follow our intuition or “gut feeling” or how we feel “butterflies” in our stomach when we feel anxious or nervous!

While our tongues tell our brains what we like, our guts tell our brains what we need. It’s essential to understand this connection between the gut and the brain that drives our cravings.

Dietary sugar and fats are some of the necessary building blocks for survival. Carbohydrates (sugars), fats (lipids), and proteins (amino acids) are a source of energy for us. When we eat calorie-dense/nutrient-dense food, which oftentimes is high in sugar and fat, the sugar and fat bind to special receptors in the gut which send signals to neurons in the information highway, or gut-brain axis. These signals travel to the brain and activate the reward center in the hypothalamus to release the “happy hormone” called dopamine (3). We eat these high-sugar and high-fat foods and feel good. This positive reinforcement is what keeps us going back for more, more, more!

Our gut has receptors that recognize sugar and fat molecules, but can our brains tell the difference between real sugar and artificial sweeteners? And which one are we more compelled to drink?

A group of researchers from Columbia University explored this gut-brain axis using mice that lack these receptors, so they cannot taste either sugar or fat. Their ‘gut feeling’ might surprise you!

First, these mice were given sugar (4). Many of us love sugary drinks like fruit drinks, sports drinks, energy drinks, and even sweetened teas. The same can be said for these mice.

When mice are given the option between sugar and artificial sweetener, the mice show a clear preference for sugar despite being genetically engineered to lack sugar receptors. So even with diet sodas and artificial sweeteners, our brains can tell the difference.

Then the researchers studied this phenomenon in mice with fat (5). Just like with sugar, when mice were given a choice they exclusively chose fatty water. Even without fat taste receptors, the mice were nonetheless driven to drink the fatty water.

“The gut is the source of our great desire for fat and sugar,” says Dr. Zuker, a professor at Columbia University. 

These findings in the gut-brain axis show how sugar and fats directly impact our brains and our behavior towards certain foods like high-calorie sugary and fatty foods. Because overconsumption of these foods can lead to negative health outcomes (e.g., obesity and type 2 diabetes), this research may lead to targeted strategies that will curb our insatiable appetites. 



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