Understanding Your Brain’s “Hunger Switch”

Ever forgotten to hydrate during a swim workout? Or run straight through an aid station because you didn’t feel hungry and regretted it later? Of course you have—and there’s a neuroscientific explanation for that.

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You know the feeling: The panic that hits toward the end of a ride when you realize you’re starting to hit a wall—just in time for that last gnarly climb. Despite your nausea, you shove a couple chews into your mouth, but it’s too late. You bonked, and you’re not entirely sure why. After all, you ate at all the appropriate intervals, just like you planned.

Fueling for optimal performance is a tricky beast, partly because the brain’s involved. You can crunch numbers all day long in an attempt to calculate the ideal number of carbohydrates per hour or what percentage of your diet should be healthy fats. But sometimes, your most precise efforts fall short. Why does this happen? Well, it all has to do with the neuroscience of hunger—and it’s pretty darn fascinating.

RELATED: 5 Signs You’re Not Eating Enough

The neuroscience of hunger

Let’s first understand how hunger works under normal conditions, before complicating matters with the highly demanding activity of endurance training. 

The brain’s response to hunger is largely regulated by the “hunger switch” and a couple key hormones called leptin and ghrelin. When your body is well-fed, leptin is released into the bloodstream and travels to the brain. Once there, it goes directly to a cluster of cells within a region called the hypothalamus, which turns on the “hunger switch.” A 2021 study in Science revealed that the “hunger switch” is actually a type of cell called melanocortin receptor 4 (MC4). When MC4 is activated, the brain sends the signal that energy levels are good, so food intake can decrease and energy expenditure can increase. 

Conversely, when your body needs fuel, your gut releases ghrelin. This hormone also travels to the brain, but turns off the MC4 switch, signaling a need for both food and energy conservation. Imagine that your brain is an engine and MC4 is the fuel gauge. When MC4 is on, the light is green, your tank is full and you’re good to go. When MC4 is off, the light is red, your engine is starting to shut down and it needs fuel before continuing to exert energy. 

Your brain is tricking you

Have you ever forgotten to hydrate during a swim workout? Or run straight through an aid station because you didn’t feel hungry? Of course you have—and there’s a neuroscientific explanation for that. In most cases, the hunger mechanism functions in a pretty straightforward way. However, under physically demanding conditions, such as swimming, biking, and running, another neurobiological pathway is triggered, one that reduces food intake. 

Think back to that region of the brain called the hypothalamus, where the MC4 “hunger switch” is located. Well, an interesting study revealed that the hypothalamus also houses another type of neuron with receptors called TRPV1. These TRPV1 receptors are heat sensitive, springing into action when body temperature rises. So, when you engage in aerobic exercise (such as swimming, biking, and running), your TRPV1 receptors activate and suppress the hunger response, curbing your appetite.

RELATED: Want to Avoid Bonking? Learn the Science Behind It

But what about the opposite effect? Does your hunger ever feel insatiable? Do you ever find yourself staring into the fridge a mere 30 minutes after a huge, post-training brunch? Well, your brain’s likely responsible for that as well. Researchers recently identified a subset of neurons, called aDCN, in the cerebellum (also known as the “little brain”) that activate when animals consume enough calories and then signals them to stop eating. So, researchers think that insatiable hunger might have something to do with dysfunctional signaling (even temporarily) of these neurons. 

OK, we’ve established that our body’s physiological need to survive drives a hunger network in the brain that is made up of checks and balances. But it should come as no surprise that there’s another hunger circuit in the brain that has less to do with need and more to do with craving. This pleasure-driven hunger is the one that muddles the way we interpret our body’s real hunger cues. When we see a desirable food, particularly something fatty or sugary, the brain’s motivation/reward pathway is activated, dopamine is released, and we feel good. As we lean into our cravings and eventually flood the brain with dopamine, the brain becomes desensitized, requiring us to consume even more not-so-healthy foods to produce the same pleasurable effects. It’s a pretty vicious cycle. 

Mindful eating and how to practice it

Clearly, the brain regulates hunger through a variety of complex mechanisms, and sometimes, we misinterpret the cues. So, how do we know when our body actually needs fuel versus when our emotional mind is tricking us into thinking we’re hungry?

The answer isn’t entirely clear yet, but mindful eating is a solid starting point. Mindful eating (or intuitive eating) is about cultivating a better relationship with food, so that you are acutely aware of how it makes you feel and how it affects your performance. The purpose of eating is to equip your body to meet the demands of both sport and life. While there are certainly practical elements to keep in mind (e.g., caloric intake, energy expenditure, a good ratio of carbohydrates/fats/protein), everybody (and every body) is different, so it’s your responsibility to learn your unique hunger cues and distinguish physiological need from emotional craving.

RELATED: The Art of Mindful Eating

Here are three suggestions for how to integrate mindful eating:

  • Adopt a curious mindset. Approach nutrition non-judgmentally and with curiosity. You are the scientist of your own body and performance, so experiment with what works for you nutritionally. Balance practical guidelines with your own inner wisdom.
  • Re-fuel before you hit empty. We all know that letting your car’s gas tank (or battery) get low is a risky move. Same is true for eating. If you wait until your body’s screaming at you to eat (i.e., cramps, headache, difficulty concentrating), then you’re putting your health and your performance in jeopardy. Plus, you’ll almost certainly overindulge when you finally do eat.
  • Pay attention to your body’s signals. Of course, there will be times when you forget to refuel. Since your body is a more reliable indicator of hunger than your mind, it’s important to become intimately aware of your body’s hunger signals. The more present you are with how your body feels as you train or move through your day, the better you’ll be able to support your body’s needs by increasing the frequency of meals/snacks or changing the type of nutrition you’re consuming.
Daya Grant, Ph.D. is a certified mental performance consultant (CMPC), neuroscientist, and yoga teacher who empowers athletes to get out of their own way and tap into their greatness. She swims, bikes, and runs in Los Angeles, where she lives with her husband and their young son.