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Why we can always make room for dessert

September 4, 2012 in News

Has this ever happened to you?

You ate a good, sensible, balanced breakfast. You feel satisfied.

Then you get to work, and the first thing you see is that your coworker brought in a box of fresh doughnuts. Suddenly, you don’t feel full anymore. In fact, you feel like you’ve got plenty of room for a doughnut. Or two.

If so, you aren’t alone. In fact, this phenomenon is so common that a group of Italian researchers decided to conduct a study to try to identify why it occurs. They wanted to see if there is a hard-wired, physiological process that keeps us hungry for tempting foods even if we feel full, or have already eaten enough fuel to keep our bodies running.

Although the study was very small, involving just 8 participants, the researchers found evidence that the human body is actually “programmed” to reward itself for overeating tempting, high calorie foods, even past the point of fullness.

Each participant attended two eating tests one month apart. At both, they were given a 300 calorie breakfast that was 77 percent carbohydrates, 13 percent fat, and 10 percent protein. After eating, they were asked to rate how hungry they were. They were then asked to wait an hour.

After the hour passed, participants were presented with what they had previously said was their favorite food. For five minutes, they were asked to rate their level of hunger, how strong the urge to eat their favorite food was, and how much they intended to eat.

In the second eating test, the setup was the same, but instead of being presented with their favorite food, participants were presented with an unappetizing food, such as a combination of bread, milk, and butter without sugar. These unappetizing foods contained exactly the same amount of nutrients and calories as each participants’ favorite food.

What happened? Despite reporting that they felt satisfied after the 300-calorie breakfast, the participants said their urge to eat and the amount they planned to eat was significantly higher when presented with their favorite food then when compared to the unappetizing food.

The research team also took blood samples at various points during the eating tests so that they could study two different chemicals. The first, a hormone called “ghrelin,” is produced in the stomach, and helps regulate reward and motivation associated with eating. The other, “2-AG” (2-arachidonoylglycerol), is an important factor in regulating appetite.

When participants ate their favorite food, their blood levels of ghrelin increased significantly, and remained high for as long as 2 hours. However, when they ate the unappetizing but nutritionally equivalent food, their blood levels continually decreased during the same time period.

2-AG levels decreased after eating both foods, but were much higher before and after the favorite foods were presented.

What the study suggests is that even if you are full and don’t need the extra energy, your body responds to the presence of an appetizing food by increasing the levels of two different compounds that make you feel an urge to eat.

Why would we be programmed this way? Nothing conclusive has been proven, yet, but one of the theories is that this an evolutionary survival mechanism. Most of human history has involved a basic struggle to eat enough food to survive. Being able to consume a sudden unexpected windfall of calories, even past the point of uncomfortable fullness, to store the energy for a rainy day could have helped our ancestors survive. This kind of drive, reinforced by cultural traditions of feasting (like Thanksgiving), is hard to extinguish.

Nowadays, with food relatively plentiful and cheap, and often served in huge portions, all these factors turn a body process that used to be an ally into a barrier. It can be very hard to resist the urge to overeat in the presence of so much food – your body still thinks we live in times when it cannot plan on the next meal coming soon.

Like anything else, learning to recognize these physical impulses takes time and practice. But while it will take a long time for these preliminary results to lead to any new treatments, the information the study provides about how your body works can give you one more argument against eating that doughnut.

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