Meet the “Hunger Hormones”: Leptin and Ghrelin

If we know anything, it’s that weight loss is complicated. Many people are told to eat less and exercise more in order to drop the excess pounds. But if it were that easy… then why is it so hard?

In truth, one size does not fit all in weight loss—genetics and the hormones in your body can have an outsized role in the struggle to lose weight. Two of these hormones that scientists have connected with weight are the two “hunger hormones,” leptin and ghrelin. 

In some people who are overweight or obese, these two hormones may be out of balance. Both of these hormones have receptors in the brain to send signals to the body about hunger levels—though they have opposite goals.

Leptin: Eat Less
The hormone leptin helps the body regulate energy balance and body weight by sending signals to the brain to reduce food intake. The majority of the leptin in your body is produced by adipose tissue–aka fat cells. Fat cells release leptin into the bloodstream, where it eventually reaches leptin receptors in the brain. Once activated, the brain sends out another signal to stop eating.

Many factors go into an individual’s leptin system, including body fat, how much food you eat, gender, age, and exercise level. There can also be a genetic component to leptin. Essentially, a mutation in a gene causes the body to naturally produce less leptin. This can then lead to difficulty feeling full after eating and over-eating to compensate. However, this is not the issue impacting the majority of individuals with excess weight. 

Leptin Resistance: Let’s Keep Eating
Why aren’t the natural levels of leptin production in the body enough for our brains to turn off the hunger signal? If everything was working as intended, someone who gained a lot of weight (specifically fat, not muscle) would then produce more leptin to suppress their eating to balance their weight. This is, in fact, not the reality.

People who are overweight or obese often have abnormally high levels of leptin. Scientists believe leptin resistance can occur in obese individuals. The brain has been bombarded with so much leptin being produced by all the fat cells that it stops listening to those signals. Leptin—the signal to reduce eating—becomes background noise, and we continue to eat. 

Ghrelin: Eat More
Where leptin tells the body to eat less, ghrelin has a different angle—eat more. Ghrelin is primarily produced by the stomach and encourages food intake. This hormone also heads to the brain, where it connects with its receptor and sends out the signal that we’re hungry and it’s time to eat. 

Similar to leptin, ghrelin levels in the body are regulated by many factors, including food intake, age, gender, BMI, and blood glucose levels. Researchers also believe weight loss surgery can reduce the production of ghrelin by the stomach, helping patients eat less and reduce weight. 

However, if you restrict calories naturally by consuming less food, the body reacts by producing more ghrelin. You eat less, and the body makes you feel hungry because it thinks you aren’t getting enough food. This phenomenon may be connected to why it is hard to lose weight by just eating less. 

Ghrelin is also connected to that other part of eating—for pleasure. The hormone is connected to emotional eating, encouraging the body to eat as a reward or a way to reduce stress.

What This All Means for Losing Weight
Scientists are still studying these two hormones and how exactly—if at all—leptin and ghrelin interplay with each other. Not only may this help us understand more about the body’s hunger cues, but researchers are also interested in exploring potential opportunities to use these hormones to treat chronic obesity. 

Gaining weight can change how your body operates from the inside out, and diet and exercise may not be enough for every individual to reach their goal weight. Medical weight loss options are growing—so talk to your healthcare provider to see if one could be right for you. 

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