There’s evidence that two hormones have much influence on our hunger and satiety levels. Let’s look into the science behind them.

Lovin’ Leptin: The Satisfaction Hormone

Fat produces a chemical signal in your blood to stop eating. It’s self-regulating. The problem happens when we override our internal monitor system and continue eating after we’re full.

Fat curbs appetite through the important chemical in weight-reduction: leptin—a protein secreted by stored fat.

The stimulation of leptin shuts off your chemicals and triggers you to burn calories, by stimulating CART.

Unfortunately, leptin doesn’t always work the way it’s supposed to.

MORE: Outsmart Your Eating Instincts

When given to rats, it decreased appetites, as it should. When given to humans, it made them thin… then something strange happened: They overcame the surge of leptin and stopped losing weight. A surge from the pleasure center in your brain can overrule leptin’s full message.

This doesn’t mean that leptin will always lose the chemical battle. The challenge is to make leptin do its job so the brain demands less food.

If you walk 30 minutes a day and build some muscle, your cells will become more sensitive and responsive to leptin.

MORE: Exercise & Your Appetite: The Truth

Ghrelin Is the Gremlin: The Hunger Hormone

When your stomach’s empty, it releases a feisty chemical called ghrelin. This stimulates NPY. If you diet by deprivation, ghrelin secretion will increase and send more signals to eat! This obviously helps override your willpower, causing chemical reactions that give you little choice but to submit to cookies.

Ghrelin also increases the release of the growth hormone (building you up and out). Your stomach secretes ghrelin in pulses about every half hour. This sends subtle impulses to your brain. When you’re really hungry (or dieting), the messages come every 20 minutes or so. And, they’re amplified. After long, your body can’t ignore the messages. It’s nearly impossible to fight the biology of your body.

The vicious chemical cycle stops when you eat. Your stomach needs to be full to reduce your ghrelin levels and appetite. If you could keep those ghrelin gremlins from making so much noise, you’ve got a chance.

Use Food to Work With Your Hunger Systems

Good news! You can control the satiety center with your food choices. Food is a drug, making different chemical reactions take place and sending messages throughout your body.

You set the tone for these orders through food. Eat the right foods (nuts) and your hormones keep you feeling satisfied. Choose the wrong foods (simple sugars) and your body goes haywire hormonally. You can become addicted to harmful foods.

A major gang leader against your body is fructose, from high-fructose corn syrup (a sweetener in many processed foods). When you eat calories from healthy foods, they turn off your urge to eat, inhibiting production of NPY or producing more CART.

But fructose in soft drinks and salad dressing isn’t seen as a regular food. This is why your body wants to keep eating. So, even low-fat foods can have bad consequences. Americans went from not eating fructose at all (in the 1960s) to eating more than 63 pounds of it each year (128,000 calories worth!).

These foods prevent you from shutting off your appetite. They’re also rich sources of calories. On a more serious note, the high-fructose corn syrup can overwhelm your liver, causing inflammation.Your liver has to process it through another pathway that produces inflammatory substances. These can damage your arteries and immune system too, increasing your risk of heart disease and cancer.

MORE: 6 Foods That Make You Hungrier