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Learning About Proteins, Carbohydrates, Calories, and Fat

Reviewed by: Mary L. Gavin, MD

Think for a minute about the last time you went to the supermarket. What do you remember seeing as you walked through the store?

    (a) a little baby in a shopping cart pushing over a gigantic display of canned corn
    (b) people with filing cabinets full of coupons
    (c) a vending machine with just the prize you wanted
    (d) five people all trying to reach for the last cantaloupe
    (e) thousands of food packages with these words on them:

      "Low fat!"
      "Protein enriched!"
      "Low calorie!"
      "FAT FREE!"
      "Good source of complex carbohydrates"
      "LITE - now with reduced calories!"

If you chose (e), you're probably like most people. In fact, you probably saw all these words and more - but what do the words mean? What are proteins, carbohydrates, fat, and calories anyway? We must need them for our bodies, but how do we get them? Don't head to the vending machine just yet - we're going to get to the bottom of proteins, carbohydrates, fat, and calories! 

Protein: On the Scene!

Even though it sounds like just one substance, protein (say: pro-teen) is really a combination of many chemicals called amino (say: ah-mee-no) acids. Scientists have found 20 different amino acids in protein, and these 20 amino acids can combine in lots of ways - in fact, they have joined together to make thousands of different proteins!

Some types of amino acids are made by you, right inside your body, without you ever thinking about it or doing anything special. These are called nonessential amino acids, and there are 11 of them. And they are necessary - meaning you need them to keep your body in tip-top shape - but they are not essential as part of the food you eat. The essential amino acids - all nine of them - must come from food. No matter how hard you concentrate or how still you sit, your body won't ever make essential amino acids. That's where eating foods with protein comes in, to give your body the amino acids it needs.

Why Do We Need Protein?
This is one nutrient that's VIP - Very Important Protein! Protein is so important that your body needed it and used it even before you were born. Your body uses protein in lots of ways. Protein's biggest job is to build up, keep up, and replace the tissues in your body. Your muscles, your organs, even some of your hormones are made up mostly of protein. Making a big muscle? Taking a deep breath with your big lungs? Running down the street on your strong feet? You've got the power of protein!  

Protein helps your body in other ways, too. It likes to make sure things get around by making hemoglobin, the part of red blood cells that carries oxygen to every part of your body. It even makes antibodies, the cells that fight off infection and disease. And the next time you fall off your bike and scrape your knee, call for protein to the rescue - it's what helps make your cuts and scrapes heal!

It's easy to get the protein your body needs. Protein is in tasty foods like meat, chicken, fish, eggs, and nuts. And you'll want to say, "More protein, please!" every time you eat some cheese - dairy products like cheese, milk, and yogurt are good sources of protein. And don't forget your bean - your lentil beans or peas, that is! These guys are full of protein.

The Great Carbohydrate
Carbohydrates
(say: car-bo-hi-drayts) are sometimes also called carbs or carbos, and your body can make them. Carbs come in two different types: sugars and starches. Sugars are called simple carbohydrates. They are called simple because your body digests them quickly and easily. Simple carbs are usually sweet tasting, like cookies, candy, soda, and other sugary foods. And some foods from nature - like many fruits - are sources of simple carbohydrates.

Starchy carbohydrates have their own name, too: complex carbohydrates. These carbohydrates take longer to be digested than simple carbohydrates do. Complex carbs are found in foods like bread, noodles, and rice, and in lots of tasty veggies.

Why Do We Need Carbohydrates?
Carbohydrates have an important job: giving all the cells in your body the energy they need! When you eat foods with carbohydrates in them, your body breaks them down into two different types of fuel.

For energy that you'll use right away, your body takes those carbs and turns them into glucose (say: gloo-kose). Glucose is carried in your blood to all the cells in your body, and gives you energy. It powers every part of your body. Glucose lets you run, jump, think, blink, breathe, and more. Want to swim up and down the coast? Or just make a tiny piece of toast? Whatever you do, as long as you're using your body, you need the great power of glucose. Have you ever felt hungry and found it kind of hard to think? That's because you were running out of glucose, and your brain needed more fuel.

But your cells can only use so much glucose at one time. So when there is glucose left over that can't be used right away, your cells save it. But there's no sticking it in the refrigerator like regular leftovers - instead, this leftover glucose is stored in your liver and muscles, and it's called glycogen (say: glie-ko-jen). The glycogen that doesn't fit into your liver and muscle cells is turned to fat.

Glycogen hangs out until it's needed, and is then released for quick energy when you're exercising. Your body decides to release the power from either glycogen or fat depending on the type of sport or activity you're doing, and how long you're doing it. If you're sprinting or doing another quick exercise, your body calls on glycogen for energy. But if you are exercising for a long time, your body turns to its "reserve tank" of fuel for energy: fat.

How Do We Get Carbohydrates?
Carbohydrates are in lots of foods, but carbs are very different from each other - and if you guessed that complex carbs are different from simple carbs, you're right! That's because simple carbohydrates are absorbed into your blood much faster, and while they provide some really quick energy, they can often come with lots of fat and lack important vitamins that your body needs. So while a can of soda or a candy bar every once in a while isn't too bad, you wouldn't want to make these simple carbohydrates a regular part of the food you eat.

Many fruits are a good source of simple carbs, though - so if you're looking for some quick energy and a healthy snack, these are the way to go! Apples, bananas, grapes, and raisins pull out in front of the simple carbs pack. And fruit cocktail, oranges, and pears will get carbs in there. Finally, don't forget to say yum to ice cream and frozen yogurt - both are good ways to get simple carbs, as well as fat, protein, and other vitamins and minerals.

Complex Carbohydrates
Complex carbohydrates
are the slowpokes of the group: they give you energy more slowly. They take longer to be digested, so your body needs more time to release these carbs into your blood as glucose. Complex carbs are better when you are exercising or playing in a game, because you can count on them to give you energy that lasts through the ninth inning or the fourth quarter! Complex carbs also beat simple carbs because they usually come with lots of vitamins and minerals your body needs.

It's easy to get the complex carbs your body likes to use as fuel - they are in bread, cereals, and pasta. And if you think complex carbs sound nice, then help yourself to a bowl of rice! It's a great source of complex carbs, just like oatmeal, pretzels, and even bagels. If you're a very veggie kind of kid, then you're in luck, because corn, potatoes, sweet potatoes, tomatoes, carrots, cucumbers, lettuce, and peppers are all great ways to get complex carbs.

All That Fat
Fat is the body's major form of energy storage, and our bodies can make fat. Many fats that people eat are really a combination of two different types of substances: saturated fatty acids and unsaturated fatty acids. Saturated fatty acids come from animal foods like meat, milk, cheese, and some oils that come from plants. Unsaturated fatty acids are different - they come from plants and fish. Together, these two substances are grouped and called the fat content in food.

Fat sometimes sounds like it's always a bad thing that people should not eat, but actually our bodies need some fat to work correctly. Fat insulates our bodies from the cold and provides some cushioning for our organs. Fat gives our bodies energy. Some fats help to make up important hormones that we need to keep our bodies at the right temperature or keep our blood pressure at the right level. Fat helps you have healthy skin and hair. And fat is like your body's very own storage and moving service: it helps vitamins A, D, E, and K hang out and get transported through your bloodstream when your body needs them!

How Do We Get Fat?
Even though our bodies need some fat to work properly, they don't need as much as most people eat. It's a good idea to avoid eating a lot of fat, because it can contribute to obesity (when a person weighs much too much for his or her height) and other illnesses that can occur when you're older, like heart disease or adult-onset diabetes.

But foods with lots of fat in them taste good - like cookies, chocolate, and fast-food hamburgers and french fries! It's OK to eat cake and ice cream at someone's birthday party once in a while. But the real trick is not to eat these kinds of foods all the time, or even most of the time. Instead, you should eat them in moderation - that means eating only a little bit at a time and not very often. Staying healthy and keeping your body in shape is easier when you go for foods and snacks that are lower in fat - and you'll feel better, too!

Checking Out Calories
Maybe you've seen low-calorie foods or low-calorie dinners on menus before. Some candy and soda commercials advertise that they have just one calorie. But what is a calorie, anyway?

A calorie (say: cal-er-ee) is a measure of how much energy the nutrients protein, carbohydrate, and fat can supply your body. When you eat food, your body uses the food as fuel, burning it to produce energy, or calories. Every person's body needs energy to function. Whether your body is doing things you don't even think about, like pumping blood or blinking, or doing things you plan, like walking a dog or blowing bubbles, you always need calories!

Some types of nutrients have more calories than others. When you eat foods with protein, every gram of protein gives you four calories (a gram weighs about the same as the amount of sugar that's in a packet at a restaurant). Same deal with carbohydrates: when you eat foods with carbohydrates, your body burns the food as fuel and gives you four calories for every gram of carbohydrate. And fat gets its reputation for being fattening because when your body burns it, you end up with nine calories for every gram of fat! That's more than twice the amount!

1 cup of milk has 8 grams of protein, so:

8 grams X 4 calories = 32 calories from protein (that's 32 calories for you from the animal who says moo!)

1/2 cup of cooked spaghetti has 17 grams of carbohydrate, so:

17 grams X 4 calories = 68 calories from carbohydrate (use your noodle and eat spaghetti for lots of energy!)

1 order of "large fries" from your favorite fast-food restaurant has 22 grams of fat, so:

22 grams X 9 calories = 198 calories from fat (uh-oh, what's that? Lots of calories from fat!)

So if it's energy your body is after, you might think that the large fries would be best, since they give you so many calories, right? The answer is. . .nope! That's because your body can only use so many calories at one time. Whatever calories your body doesn't burn for fuel, it stores in your body as fat. So even though they taste good, foods that get a lot of their calories from fat aren't quite as great as they seem. . .in fact, if you eat a lot of them, you can end up gaining weight.

The key to keeping your body healthy is to remember that your body uses food for energy. When you are active, your body burns lots of calories to let you kick that ball far or run fast. But when you are watching TV or a movie, your body doesn't burn nearly as many calories - you just don't need that much energy to laugh at your favorite show!

So the trick to keeping your body at a weight that's good for your height is to eat as many calories as you burn off. If you eat more calories and exercise less, the energy has nowhere to go, and you gain weight. The more you exercise, the more calories you can have, because there is a good balance between the two. But don't forget, it's still a good idea to get most of your calories from protein and carbohydrates. Fat won't hurt you if you eat it in moderation (moderation means eating it a little bit, and not very often), and it tastes good, but fat should make up a little less than 1/3 of all the calories you eat.

Reviewed by: Mary L. Gavin, MD
Date reviewed: November 2015

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