By Peter M. Vishton, Ph.D., William & Mary

Edited by Kate Findley, The Great Courses Daily

When it comes to managing healthy eating habits, we need to listen to what our body is telling us. Are we eating because we’re truly hungry or are we eating because we’re bored? Peter M. Vishton, Ph.D., describes the hormones that alert us if we’re hungry or full—and why it’s not wise to try and “game the system.”

Leptin and Ghrelin: Regulating Hunger

Many brain mechanisms are involved in regulating hunger and satiation. Two hormones called leptin and ghrelin play a major role.

Leptin is produced by the fat cells in our body. Ghrelin is produced by cells that live in our intestines. The amount of these hormones that gets released are strongly influenced by our eating behaviors. 

Fat is an amazing energy storage mechanism that the body uses. Excess energy is converted into fat. 

When we run low on energy, fat is converted back into a form that can be used to power any cell in our body. Whenever our body starts storing energy and converting excess energy to increase the content of fat cells, leptin is released by the fat cells into the bloodstream.

The leptin travels through your bloodstream and eventually passes into the brain. Some of the leptin reaches the hypothalamus, in a region called the ventromedial nucleus. 

From there, leptin binds with neuronal receptors and boosts activation of certain neural circuits. When these circuits are active, you feel full and typically stop eating. 

Ghrelin does the opposite. When your intestines finish processing food, they start making ghrelin. As time passes, they continue making more and more ghrelin. Like leptin, ghrelin makes its way to the brain and causes you to start feeling hungry again.

Why Leptin Matters

Together, these systems regulate food intake. If you feel hungry or full, your eating behaviors will tend to behave accordingly. These are mechanisms that drive your subconscious eating behaviors.

We often decide to eat for reasons other than hunger. If you’re at a dinner party and the host puts out food for everyone, there are social proprietary reasons to eat at least a little bit. 

However, most of our eating, particularly our sense of how much to eat and when to stop eating, are regulated by this leptin and ghrelin system. Disruptions of these systems can have dire consequences. 

The hormones were initially discovered in a strain of mutant mice who would just eat and eat and eat—they would get very fat in the process. Without that leptin to tell the mice that they were full, they kept consuming more and more calories.

Can You Fake Fullness?

Several companies market leptin supplements that will create an artificial sense of fullness by introducing extra leptin into the bloodstream. This works in the short term, but the leptin system, like most others in the body, is adaptive. 

Coffee drinkers know all about how the body adapts. The first few times you drink coffee, the caffeine travels to the brain and produces a strong boost in arousal. 

However—especially if you tend to drink coffee at about the same time and same place every day— your brain learns that and compensates for it. As the time for coffee approaches and you smell the coffee brewing in the pot, your brain knows that the stimulant is coming. The brain then downregulates activity just enough so that when the coffee arrives, it boosts you right back up to where you would have otherwise been.

Eventually you need that coffee, not for a boost above normal levels of arousal, but just to maintain your typical level. If you’re a heavy coffee drinker, skipping the coffee will sometimes produce a headache, as the brain inhibits its activity, and you aren’t boosting it back up with coffee. 

The same happens with leptin supplements. They’ll work for a while, but they’ll quickly lose their effectiveness, and if you stop taking them, you’ll be subject to a very strong hunger sensation.

In summary, leptin and ghrelin do a good job of telling your brain about what’s going on in your gut. If the digestive process is done, and if your fat cells are releasing energy into the bloodstream just to keep things going, there’ll be very little leptin and a lot of ghrelin, and your stomach may be growling. You will feel hungry. 

Conversely, if there’s not so much ghrelin, but a lot of leptin, that means you still have food left in your digestive tract and likely will not be thinking about food. Therefore, it’s important to listen to your body’s signals and not to attempt to artificially influence your hunger hormones. 

This article was edited by Kate Findley, Writer for The Great Courses Daily.

Dr. Peter M. Vishton is Associate Professor of Psychology at William & Mary. He earned his Ph.D. in Psychology and Cognitive Science from Cornell University. Before joining the faculty of William & Mary, he taught at Northwestern University and served as the program director for developmental and learning sciences at the National Science Foundation.