Food and Energy

Why do we need to eat?

Have you ever wondered why you need food? The most obvious answer is energy. You need energy to climb stairs, lift books, run, and even to think. Just as a car needs gasoline, your body needs fuel, and food is that fuel. Molecules in food contain chemical energy that cells use to produce ATP. Food also supplies raw materials your body needs to build and repair tissues.

Energy The energy available in food can be measured in a laboratory in a surprisingly simple way—by burning it! When food is burned, most energy in the food is converted to heat, which is measured in terms of calories. A calorie is the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius. The “Calories” you've heard about in food are actually dietary Calories, written with a capital C. One dietary Calorie is equal to 1000 calories, or 1 kilocalorie (kcal). As you may recall, the energy stored in food molecules is released during cellular respiration and used to produce the ATP molecules that power cellular activities.

Raw Materials Chemical pathways, including cellular respiration, can extract energy from almost any type of food. So why does it matter which foods you eat? The reason is that food also supplies the raw materials used to build and repair body tissues. Some of these raw materials are needed to make enzymes, the lipids in cell membranes, and even DNA. In fact, food contains at least 45 substances that the body needs but cannot manufacture. A healthy diet ensures that your body receives all of these required substances.

In Your Notebook Prepare a table to fill in with information about the nutrients. For each nutrient, include foods in which it is found and describe its role in the body.