Dopamine Might be the Reason for Your Midnight Snacking

by Bailey Sasseville

Diets are a hot topic in American society right now. It seems like every day a new fad diet is proclaimed as a miracle cure for rising rates of obesity and associated conditions like heart disease and diabetes. Part of the reason for this weight increase seems obvious — we eat a vastly different diet than we used to, ditching the fruits and vegetables for fatty, sugary, processed goods mass marketed for prices cheaper than healthier items. We’ve switched out fresh broccoli for processed cheesy broccoli. But even when we make efforts to eat healthy foods, diets are notoriously hard to stick to, especially when we seem to be surrounded by more donuts than apples.

To determine if the change in American diets is due to availability, a recent study evaluated the U.S. food supply to determine how healthy available foods are. Researchers used a scale developed by the Australian government that analyzes both good and bad nutrients in food products to rate items from 0 to 5, with 0 being the most unhealthy. Foods weren’t considered “healthy” without a score of at least 3.5 or above. For all food products, the average score was 2.7 — meaning most food products available to Americans are unhealthy. The study also rated how processed food products are, examining both the extent and the purpose of processing, and found that a whopping 70.9% of foods are ultra-processed — a far cry from the fresh produce our ancestors used to eat. But how exactly does this food supply affect us?

Researchers as the University of Virginia conducted an experiment that mimicked this unhealthy food environment using mice as a model. When the mice had access to food high in fat and sugar, they became obese, but also ate more food than mice that had access to regular food, and began eating at times when they would normally be sleeping. In short, they gained weight and changed their normal patterns of behavior when they ate unhealthy food. 

Next, researchers wanted to find out how eating unhealthy food led to a change in behavior in the mice. After all, why wouldn’t the mice just stop eating once they had consumed enough calories? They suspected that dopamine, a molecule that travels throughout our body to help control our behavior, had something to do with it. You might know dopamine as the feel-good molecule, and indeed previous research has connected it to reward pathways that cause us to crave foods. To test this, the researchers created a population of mice that didn’t have a certain kind of dopamine receptors, which detect dopamine and transmit a signal, therefore blocking out any dopamine signaling in the mice. Then, they repeated the experiment and gave these dopamine receptor-less mice unlimited access to food. When these mice were given access to high-fat foods, they didn’t become obese — they just ate until they had enough calories, similar to mice given regular foods. Additionally, they maintained their normal rhythms of behavior, and only ate during their regular foraging periods, comparable to a person only eating during daylight hours. 

From this, researchers concluded an unhealthy diet packed with fat and sugar triggers a surge in the dopamine signaling pathway that leads to overeating in both amount and timing. Further research showed that this signaling occurs in a region of the brain called the circadian pacemaker, which controls many behavioral and bodily rhythms that occur over 24 hours, like the sleep cycle and, of course, the eating cycle. Assuming this evidence is transferable to humans, not only does a high-fat diet give us extra calories, it encourages us to eat outside our regular schedules and eat more overall, leading to further metabolic issues.

Evolutionarily, this mechanism might have been an advantage. If humans had irregular access to food, it made sense to “overeat” when energy-rich food was available, because it could be stored as fat to last through long periods without food. In today’s environment where most people have constant access to food, this mechanism begins to work against us. Unless we take these molecular pathways into consideration, fad diets will only ever be fads.