Fuel you can't see

About this video

You skipped breakfast, you feel slow and it is hard to think. You eat some bread and cheese, and soon you are ready to go again. What did the food give you? Energy. Your heart beats, you breathe, your brain thinks, you keep warm and you grow, and all of it runs on the energy in what you eat and drink.

The energy in food is measured in kilocalories (kcal), which most people simply call calories. Some labels also give kilojoules (kJ): one kilocalorie is about 4.2 kilojoules, so the kJ number is always about four times bigger.

The parts of food don't carry the same energy. Gram for gram, carbohydrate gives about 4 kcal, protein about 4, fibre about 2 and water none, while fat gives about 9, more than twice as much as the others. These are the conversion factors food labels use in the European Union.

How much does a body need? The NHS says an average woman needs about 2,000 kcal a day and an average man about 2,500. These are averages, not targets: growing teenagers, bigger people and very active people need more, smaller or less active people less.

Energy balance is how the energy you take in compares with the energy your body uses. Equal, day after day, and weight stays about the same. More in than out, and the body stores the extra, mostly as fat. Less in, and it uses some of its stores. Over weeks, not one meal. But a body is not a calculator: it changes how hungry you feel, the kind of food changes how much you end up eating, and body size, shaped by many things nobody chooses, says nothing about how good or hard-working someone is. This video explains energy in food, from the lesson Food Is Fuel on Knaph.

Transcript

1. 0:00You skipped breakfast and feel slow. Then you eat, and you're ready to go again. What did food give you?
2. 0:09Energy, counted in kilocalories. One kilocalorie is about four point two kilojoules.
3. 0:17Gram for gram, carbohydrate and protein give about four. Fibre about two, water nothing. And fat about nine, more than twice as much.
4. 0:33An average woman needs about two thousand a day, an average man about two thousand five hundred. Averages, not targets.
5. 0:42Energy in and energy out. Equal, and weight stays about the same. More in, the extra is stored, mostly as fat. Less in, the body uses its stores.
6. 0:58But a body isn't a calculator. And size says nothing about how good someone is.
7. 1:06Food is fuel. Over weeks, the balance decides what's stored.