Where Does the Energy in Food Actually Go?

What Happens to Food After You Swallow It?

A granola bar does not travel down to your leg and turn into running. Your digestive system has some work to do first. It breaks food into smaller parts that your body absorbs. Carbohydrates are broken into simple sugars, including glucose. Proteins are broken into amino acids. Fats are broken into fatty acids and other smaller parts. These molecules cross from the digestive system into the body and travel to places where they are used, changed or stored. Suddenly “food gives you energy” becomes much more interesting. Your cells never see a sandwich. They receive the molecules released from it. Those molecules become part of the enormous amount of chemistry happening inside you every second to keep you alive, moving, thinking, growing and repairing.

Try it: Put these in order: nutrients travel through the body, you eat food, cells use the smaller molecules, digestion breaks food down.

What Does a Calorie Actually Measure?

A Calorie is simply a unit used to measure energy. That is it. It is not a score telling you whether a food is good or bad, and it is certainly not something your body is trying to “defeat.” Food contains chemical energy. Through many chemical reactions, cells transfer some of that energy into ATP, a molecule cells use to power their work. Muscles use energy to contract. Cells use energy to move substances, build molecules and maintain themselves. Your body also needs energy while you are sitting completely still. Breathing, circulation, temperature control, brain activity, growth and repair have not taken the afternoon off. Physical activity increases the work, but movement is only one of the many things food energy supports.

Try it: Someone says, “Calories only matter if you exercise.” Use two examples from this section to show why that makes no sense.

If Carbohydrate Provides Energy, Is That Its Main Job?

Carbohydrate is the body's main dietary source of glucose and an important source of energy. Foods such as oats, rice, bread, pasta, fruit, beans and potatoes all provide carbohydrate, although they arrive in very different food packages. The body uses glucose immediately and stores some as glycogen in the liver and muscles for later. That stored carbohydrate becomes especially useful when activity demands increase. But remember Post 1: how the carbohydrate arrives matters. Sugar or juice, with sugar dissolved in a drink, reaches digestion very differently from carbohydrate wrapped inside oats, beans or fruit with fibre and other nutrients. Both provide carbohydrate. They are not nutritionally identical. Simply asking, “Does it have carbs?” tells you far less than looking at the whole food.

Try it: Pop and an orange both provide carbohydrate. What does looking at the whole food tell you that the word “carbohydrate” does not?

If Fat Is So Energy-Dense, Why Does the Body Need It?

Fat contains more energy per gram than carbohydrate or protein, which is why we call it a concentrated source of energy. But reducing fat to “lots of Calories” misses most of the story. Fats form important parts of cell membranes, help the body absorb vitamins A, D, E and K, and are involved in many normal body processes. The body also stores fat as a major long-term energy reserve. Foods containing unsaturated fats, such as nuts, seeds, avocado and many plant oils, bring useful fats as part of their nutrition package. So “fat equals bad” falls apart pretty quickly once you know what fat actually does. Your body does not keep a nutrient around just to make nutrition lessons more confusing.

Try it: Nuts contain fat. Give two reasons why saying “nuts are bad because fat has lots of Calories” misses what nuts contribute.

Is Protein Just for Building Muscle?

No. Muscle gets all the advertising, but protein has a much larger résumé. Digestion breaks protein into amino acids, and the body uses them to build and repair tissues. They are also used to make enzymes, transport proteins and many other molecules needed throughout the body. That matters during Grade 7 because your body is growing whether or not you have ever lifted a dumbbell. Foods such as beans, lentils, eggs, yogurt, fish, tofu, meat, nuts and seeds provide protein, often alongside other nutrients. Protein also contributes energy when needed, but treating it as simply another fuel misses its major building and repair jobs. Carbohydrate, fat and protein overlap, but they are not interchangeable. Each brings something different to the body.

Try it: Your friend says, “I don't work out, so protein doesn't really matter to me.” Give them a better explanation.

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