Article # 10. Figuring Out Fat and Calories

What Are Fat and Calories?

Fats, or lipids, are nutrients in food that the body uses to build cell membranes, nerve tissue (like the brain), and hormones. The body also uses fat as fuel. If fats that a person has eaten aren't burned as energy or used as building blocks, they are stored by the body in fat cells. This is the body's way of thinking ahead: By saving fat for future use, it plans for times when food might be scarce.

A calorie is a unit of energy that measures how much energy food provides to the body. The body needs calories to function properly.

Food Labels: Calories

Food labels list calories by the amount in each serving size. Serving sizes differ from one food to the next, so to figure out how many calories you're eating, you'll need to do three things:

1.    Look at the serving size.

2.    See how many calories there are in one serving.

3.    Multiply the number of calories by the number of servings you're going to eat.

For example, a bag of cookies may list three cookies as a serving size. But if you eat six cookies, you are really eating two servings, not one. To figure out how many calories those two servings contain, you must double the calories in one serving.

When you start looking at food labels, you may be surprised at some of the serving sizes. For example, on the labels of six cold breakfast cereals, the serving size ranges from ½ cup to 1¾ cups. You would have to more than triple the smallest serving size to compare the calories in that cereal with the calories in the cereal with the largest serving size (1¾ cups). A small bag of corn chips may contain two or more servings — although most people would eat the entire bag! That's why it's always important to check the serving size of all foods on the label.  

A calorie is a unit of energy. We tend to associate calories with food, but they apply to anything containing energy. For example, a gallon (about 4 litres) of gasoline contains about 31,000,000 calories. You could drive a car 22 miles (35 km) on the calories in 217 Big Macs.

Specifically, a calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water by 1 degree Celsius (1.8 degrees Fahrenheit). One calorie is equal to 4.184 joules, a common unit of energy used in the physical sciences.

Most of us think of calories in relation to things we eat and drink, as in "This can of soda has 200 calories." It turns out that the calories listed on a food package are actually kilocalories (1000 calories = 1 kilocalorie). So that can of soda actually has 200,000 calories (but don't worry, the same applies to exercise -- when an exercise chart say you burn 100 calories jogging a mile, it means 100,000 calories). A food "calorie" is sometimes capitalized to show the difference, but usually not.

Human beings need energy to survive -- to breathe, move, pump blood -- and they acquire this energy from food. The number of calories in a food is a measure of how much potential energy that food possesses. A gram of carbohydrates has 4 calories, a gram of protein has 4 calories and a gram of fat has 9 calories. Foods are a compilation of these three building blocks. So if you know how many carbohydrates, fats and proteins are in any given food, you know how many calories, or how much energy, that food contains.

If we look at the nutritional label on the back of a packet of maple-and-brown-sugar oatmeal, we find that it has 160 calories. This means that if we were to pour this oatmeal into a dish, set the oatmeal on fire and get it to burn completely, the reaction would produce 160 kilocalories (remember: food calories are kilocalories) -- enough energy to raise the temperature of 160 kilograms of water by 1 degree Celsius. If we look closer at the nutritional label, we see that our oatmeal has 2 grams of fat, 4 grams of protein and 32 grams of carbohydrates, producing a total of 162 calories. Of these 162 calories, 18 come from fat (9 cal x 2 g), 16 come from protein (4 cal x 4 g) and 128 come from carbohydrates (4 cal x 32 g).

Our bodies "burn" the calories in the oatmeal through metabolic processes, by which enzymes break the carbohydrates into glucose and other sugars, the fats into glycerol and fatty acids and the proteins into amino acids (see How Food Works for details). These molecules are then transported through the bloodstream to the cells, where they are either absorbed for immediate use or are sent on to the final stage of metabolism, in which they are reacted with oxygen to release their stored energy.

Question: What is a calorie and why is it important to know how many calories there are in certain foods?

Answer: A calorie is actually a unit of heat energy. That's right. We think of calories as just things that are in food and all foods have calories. But your body sees calories as energy and it's energy to produce heat. And heat energy is what really fuels our body just the same way that gasoline is what fuels your car's energy.

Now all foods have calories and different foods have different amounts of calories. Calories are provided by fat, carbohydrate, and protein.

Fats have the highest concentration of calories. That's nine calories per gram of pure fat. Protein and carbohydrates each have four calories per gram of pure protein or pure carbohydrate. Alcohol, pure alcohol, has seven calories per gram. So understanding the role of calories in your diet can help you balance your calories in with your calories out, and help you achieve weight management goals.

Now you can look at, find out the calories in foods by looking at the calorie label or the nutrition facts panel on packages of processed foods. They will all have the number of calories per serving and the portion size per serving. And using these tools, you can help yourself estimate how many calories you're taking in per day and help you achieve your weight loss goals.