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United States Department of Agriculture

Agricultural Research Service

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Here Come Those Runaway Carbs!

Ever wonder why you sometimes feel REALLY hungry just a few hours after eating a big meal?

Probably, you ate the kinds of foods that put a lot of sugar into your blood very quickly. Candy, donuts and desserts do that because they contain a lot of sugar.

But so do other carbohydrates like pretzels, crackers, white bread, potatoes, white rice--even many cereals.

Each of these carbohydrates, or carbs for short, is made of sugar molecules all hooked together like cars on a train. In your intestines, these molecules quickly unhook from one another and roll on into your bloodstream--sometimes faster than eating a spoonful of sugar.

One out of every five U.S. kids is overweight. And being overweight is not healthy, says Susan Roberts. She is a physiologist at the U.S. Department of Agriculture's nutrition research center in Boston, Massachusetts. Physiologists are scientists who study how living things work by focusing on one or more of the many functions.

Even when you're just sitting still reading, your body is constantly doing lots of work! You breathe in and out ... your lungs load oxygen into blood cells ... your heart pumps blood through your body ... your brain and muscles keep you from dropping your book and falling out of your chair ... and on and on.

Roberts wants to know why so many more children are gaining weight than ever before. She thought some of the extra weight may be coming from eating carbs that "shotgun" sugar into your blood.

Some scientists already believed that it could make people want to eat again too soon. But nobody had really tested this idea. So Roberts and other scientists did.

For breakfast and lunch, they fed teenage boys one of three different meals. Each meal would raise blood sugar at different speeds. Then they measured how much the boys ate later the same day.

Sure enough, the boys felt most hungry and ate the most calories after eating the meals that raised blood sugar quickly.

But ... WHY do those "shotgun" carbs make you hungry?

When you absorb sugar into your blood quickly, your body pumps a lot of insulin into the blood. Insulin is a hormone. Its job is to help move sugar out of the blood and into your cells, where it can be used for fuel. It's like gasoline for your cells.

But with your body pumping all that insulin, the sugar leaves the blood too quickly. And when this happens, your brain gets a signal that means: "Hey! I have to eat something fast or I might starve!"

Hmmm... Your smart brain forgot that you just finished a big meal a few hours ago. Why? Because the sugar and fat from that meal isn't in the blood anymore.

So, you feel hungry and obediently go to the refrigerator looking for something to eat. When this happens again and again, guess what? You get fat. Your cells don't need that much fuel. So your body stores it as fat. And the extra fat keeps piling up.

The good news, says Roberts, is that kids can eat all the vegetables and fruits and low-fat dairy products and whole grain cereals they want. That's because the carbs in these foods take longer to get into your blood. Lean meat and poultry are good for you, too. And you won't want to pig out a few hours later.

--By Judy McBride, formerly with the Agricultural Research Service Information Staff


Science for Kids

Last Modified: 8/12/2016
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