A symphony of factors control hunger, fullness, and ultimately our weight, including everything from how well you slept last night to the accounts you follow on Instagram. Also involved in the complex process are hormones, particularly the two that are often referred to as hunger hormones, leptin and ghrelin.

In an ideal world, leptin and ghrelin work together to help keep you at a healthy weight. In the real world, well, 70% of the population ends up overweight or obese. Could out-of-whack hormones be to blame?

To answer that question, you first have to understand how the so-called hunger hormones work.

Leptin is the satiety hormone. Essentially, it tells you when to stop eating. “It makes you feel full, and it blocks appetite,” says James Shoemaker, MD, PhD, associate professor in biochemistry and molecular biology at St. Louis University.

Ghrelin, on the other hand, tells you when you’re hungry and need to eat. Think of it as the gremlin making your stomach grumble. “It’s made in the stomach primarily, and it’s released when you haven’t eaten for a while,” says Michael Schwartz, MD, co-director of the Diabetes Institute at the University of Washington in Seattle. Ghrelin peaks every four hours or so–roughly corresponding to breakfast, lunch, and dinner.

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When everything’s running smoothly, the two hormones work in harmony, says Philadelphia-based Marjorie Nolan Cohn, RDN, a spokesperson for the Academy of Nutrition & Dietetics. “As one is rising, the other one is dropping.”

But things can–and do–go wrong.

For starters, leptin levels fluctuate with how much fat you have. When you lose weight, leptin levels drop. With less of that appetite-suppressing hormone, you end up feeling hungrier and eating more, potentially causing you to gain back the weight you had lost. “[Once] you have returned to your baseline weight, leptin will have recovered,” explains Dr. Schwartz.

In fact, a study that looked at 14 former Biggest Loser contestants showed that, indeed, leptin levels declined in those who lost large amounts of weight (they lost an average of almost 130 pounds). That could explain why most of them regained much of the weight over time.

It’s also possible to become desensitized to leptin–called leptin resistance–if you are constantly stuffing yourself with food. “You’d think that if you’re eating a lot you shouldn’t be hungry, but it’s the opposite,” says Cohn, who is also author of The Belly Fat Fix: Taming Ghrelin, Your Hunger Hormone, for Quick, Healthy Weight Loss. “Even though there may be leptin in circulation, it’s not registering,” she says, and you don’t know you’re full. 

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Hunger-stimulating ghrelin levels also vary with weight loss. After dieting, ghrelin production increases, potentially causing people to eat more and gain weight. “The cravings can be so hard to control,” says Cohn. “Once you’re out of whack, it’s really hard to get back into balance.”

Why our bodies fight back

Understandably, human beings are designed to fight starvation. Part of the body’s response to dieting is a drive to revert to whatever weight we were previously. “As you gain weight, the brain thinks that the new weight is the one that’s supposed to be regulated,” says Dr. Schwartz. “That’s why it’s so hard to lose weight and keep it off.”

That response typically kicks in after you’ve lost around 5% to 7% of your bodyweight, he says. “Once you lose more than 5% of your bodyweight, on average, you’re going to engage these responses that counter-regulate against the weight loss. Whether you do it quickly or slowly, it doesn’t matter very much.”

Interestingly, people who undergo bariatric surgery seem to have lower levels of hunger-promoting ghrelin than people who take pounds off through plain old diet and exercise. This may be why weight loss after gastric bypass surgery tends to last for longer periods of time.

Harnessing your hormones

Barring surgery, is there any way you can control these hormones to your advantage? Luckily, yes.

If you can, stick to a more moderate weight loss of just around 5% of your bodyweight so you don’t trigger that debilitating drop in leptin. Then, readjust mealtime: “Eat on the clock,” says Cohn. That means every two hours if you like to eat smaller portions or every four hours if you eat larger meals. This draws down stomach-grumbling ghrelin levels.

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It’s also important to eat a balance of foods at each meal, particularly protein and complex carbs. “Protein is a major player in suppressing ghrelin,” Cohn says. “It takes more work to digest and keeps you full longer.” Fiber also slows digestion and helps keep you full, she adds. Look for complex carbs like whole grains, veggies, and fruit, especially those containing a type of fiber known as “resistant starch,” like not-quite-ripe bananas.

Exercise may also help control your hunger hormones so you can shed pounds for good. One study found that losing weight on a treadmill resulted in lower ghrelin levels than slimming down by simply eating less.