Why Do You Continue to Eat When You're Full?

      The premise that hunger makes food look more appealing is a widely held belief.

Prior research studies have suggested that the hunger hormone ghrelin, which your body produces when it’s hungry, might act in your brain to trigger this behavior.

New studies suggest that ghrelin might also work in your brain to make you keep eating "pleasurable" foods when you’re already full.

Scientists previously have linked increased levels of ghrelin to intensifying the rewarding or pleasurable feelings that can be obtained from cocaine or alcohol. Researchers observed how long mice would continue to poke their noses into a hole in order to receive a pellet of high-fat food. Animals that didn’t receive ghrelin gave up much sooner than the ones that did receive ghrelin.

Humans and mice share the same type of brain-cell connections and hormones, as well as similar architectures in the "pleasure centers" of the brain.


Dr. Mercola’s Comments:

Isn’t this really the million-dollar question? Why do people continue to eat, even after their stomachs are full or even stuffed? If there was a simple answer, I’d gladly share it with you, but the reality is that people overeat for a variety of reasons – and many of them are rather complex.

As this new study suggests, one of the forces driving you to eat a second helping or an extra dessert even though you’re full is the hormone ghrelin. Ghrelin (pronounced GRELL-in) is produced mainly by your stomach, although it is also made in other organs, such as your intestines and your kidneys.

Ghrelin has been dubbed the “hunger hormone” because in previous studies people given the hormone became so ravenous, they ate markedly more than their usual food intake. Ghrelin, it appears, may also act on your brain’s “pleasure centers,” driving you to reach for another slice of cheesecake simply because you remember how good the first one tasted and made you feel (at least in that moment).

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What Influences Your Body’s Level of the Hunger Hormone?

Your body’s level of ghrelin can be influenced by many factors, including your lifestyle habits. For instance, chronic lack of sleep increases ghrelin, making you feel hungry when you don’t really need to eat. This is likely one reason why a lack of sleep can make you gain weight.

Insulin may also play a role in regulating ghrelin levels. In one study, ghrelin levels were monitored in eight non-diabetic adults as they were given a two-hour infusion of insulin. Shortly after the infusion began, levels of ghrelin began to drop. When the insulin infusion was stopped, levels of the hunger hormone began to rise and rapidly returned to normal.

Since insulin is already known to increase levels of leptin – the "obesity hormone" that tells your brain to curb your appetite after eating – the findings suggest that insulin plays an important role in controlling what you eat.

In other words, let’s say you eat a sugary dessert. Your production of insulin increases so that the sugar in your blood can be taken to cells and used for energy. Eating this sugar also increases production of leptin, which regulates your appetite and fat storage, and decreases production of ghrelin, which helps regulate your food intake. The idea is that when you eat, your body knows it should feel less hungry.

But there is another major key here that is often overlooked, and that is when you eat certain foods, namely those that contain fructose, this important cycle does not occur.

Is Fructose Driving You to Overeat?

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Fructose, a cheap form of sugar used in thousands of food products and soft drinks, can damage human metabolism and is likely fueling the obesity crisis. This is because your body metabolizes fructose in a much different way than glucose, and fructose is now being consumed in enormous quantities, which has made the negative effects much more profound.

If anyone tries to tell you “sugar is sugar,” they are way behind the times. It is increasingly becoming clear that just by eating fructose, including high-fructose corn syrup, you may be drastically increasing your tendency to overeat.

You see, glucose suppresses the hunger hormone ghrelin and stimulates leptin, which suppresses your appetite. Fructose, however, has no effect on ghrelin and interferes with your brain’s communication with leptin, resulting in overeating.

This is why fructose may contribute to weight gain, increased belly fat, insulin resistance and metabolic syndrome – not to mention the long list of chronic diseases that are related to these conditions.

Are There Other Factors That Come Into the Mix?

Yes, ghrelin, leptin and insulin responses in your body may be major players in your ability to regulate your food intake, but they are not the only ones.

Stress, anger, sadness and just about any other negative emotion can also lead you to seek food as a coping mechanism and ultimately overeat. And subconscious cues you pick up from portion sizes, food visibility (such as passing by a candy dish on a desk) and food proximity (standing near the food table at a party) can also influence how much you eat.

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Gary Taubes, who wrote the landmark article What if it’s All Been a Big Fat Lie?, also recently offered a very interesting alternative explanation for why people overeat. He suggests that people overeat because their fat tissue is accumulating excess fat. And why does fat tissue do this?

Because dietary carbohydrates, especially fructose, are the primary source of a substance called glycerol-3-phosphate, which causes fat to become fixed in fat tissue. At the same time, this diet raises insulin levels, which prevents fat from being released.

Practical Tips to Keep Your Eating Under Control

The solution to normalizing your ghrelin, leptin and insulin levels is fairly straightforward, and this is to eat a diet that emphasizes good fats and avoids blood sugar spikes – in short the dietary program detailed in my nutrition plan, which emphasizes healthy fats, lean meats and fresh vegetables, and restricts sugar and grains.

If you want to take your health to the next level, I highly recommend finding out your nutritional type as well, and then eating a diet according to your unique biochemistry.

This, combined with a regular exercise program and a tool to handle emotional eating, will be your key to controlling your motivation to eat.

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January 20, 2010