Human energy requirements

Michael and Jenny are having pancakes for breakfast. There is only one left! That is mine. I need more energy than you! Is that true?

How do you know how much energy you need? And how much energy is there in a pancake? The food we eat contains nutrients: carbohydrates, proteins, fats and other lipids, vitamins, and minerals. Our bodies digest these nutrients and transform them into energy and various substances through METABOLIC REACTIONS. This energy is used by your body in three different ways.

Some of the energy from the food you eat is used for digestion itself. On average, digestion uses up to 10% of the energy you take in, but it also depends on the types of nutrients in your diet. Apart from digestion, energy is also used by your muscles when you move and exercise. If you play football or exercise in other ways, you will use more energy than if you stay home and read a book. Physical activity uses about 20 to 30% of the energy you get from the food you eat.

What about the rest of the energy? Well, it’s used… to keep you alive! There are a lot of processes going on in your body, even if you just sit and do nothing. These include all the vital functions of your body such as breathing, blood circulation, production of new cells, and maintaining body temperature. The amount of energy used for these processes is called BASAL METABOLIC RATE or - BMR.

Your BMR depends on several factors such as your age, sex, body size, body composition, and genetic factors. For example, energy requirements are higher in children and teenagers because their bodies need more energy to grow and develop. And on average, male bodies have more muscle mass, so they need more energy than female bodies. If you add together the energy that goes to digestion, your physical activity, and your basal metabolic rate, you know how much energy you need to supply to your body from the food you eat. But how do you know how much energy that is, and if you are eating enough?

Is there a way to measure it? There is! The energy can be measured in units called calories. 1 calorie is the amount of energy needed to heat up 1 gram of water by 1 degree Celsius. The energy our body uses is much higher, so we use kilocalories instead.

1 kilocalorie is equal to 1000 calories. Experts on nutrition have calculated a recommended daily energy intake. For teenage boys it should be around 2800 kilocalories, and for teenage girls about 2200 kilocalories a day. But remember that these numbers might vary depending on your physical activity or individual characteristics! All food products you buy in a shop have the number of calories and nutrients they contain printed on the labels.

You can often check the energy and nutritional values of different foods online too. In this way you can check if your diet is balanced, and if you eat enough to meet your daily energy requirements! Hm, let’s see. Michael and Jenny’s pancake has about 130 kilocalories. Jenny works out, but she’s older; Michael is a boy, but he is shorter.

But they both need to study... You know what? Why don’t you just cut it in half?