Science · Classes 9-10 · Chapter 1 · 1.1

Food and Nutrition: Carbohydrates and Calories.

A handful of puffed rice and a lump of molasses for breakfast. Both go down, but what does the body actually take from them? The book answers with a few definitions, six components and one unit, the calorie. In this note you will handle all three.

1. Food, nutrition and nutrients

Nutrition science does not call everything we eat food. Only the edible things that help the body make energy, grow, repair itself and resist disease, in short that nourish it, count as food.

Nutrition is a process: taking the food you need from your surroundings, digesting and absorbing it, meeting your energy need, building resistance to disease and helping the body grow.

The organic and inorganic substances in food that supply a living body with the energy it needs are together called nutrients. Glucose, minerals and vitamins are examples.

Food does three jobs: (1) it grows, repairs and protects the body, (2) it produces heat and energy, and (3) it guards against disease, keeping you healthy, strong and active.

2. The six components of food

Food has six components. Three are main: carbohydrates, proteins and fats. Three are supplementary: vitamins, minerals and water. Fibre, also called roughage, is one more important component (Fig 1.01).

Fats and carbohydrates are the energy-producing foods; proteins are the body-building food. Vitamins, minerals, water and fibre help keep the body's life processes going.

3. Carbohydrates: which sugar, where

Carbohydrates are the main food of human beings. They are built from carbon, hydrogen and oxygen, and they give heat and energy. Sugar has no colour and no smell, and tastes mildly sweet.

Starch: cereals such as rice, wheat and maize are its main source, and potato, sweet potato and arum are important too. Glucose is less sweet than sugar and turns up in grapes, apples, carrots and dates. Fructose, the fruit sugar, is in mango, papaya, banana, orange and in honey from flowers.

Sucrose comes from sugarcane, sugar, molasses and sugar candy. Cellulose is in wood apple, mango, banana, watermelon, groundnut, dry fruit and every kind of vegetable.

Two carbohydrates come from animals. Lactose, the milk sugar, is in the milk of cows, goats and other animals. Glycogen is in the meat and liver of birds such as chicken and pigeon.

During respiration carbohydrate is oxidised and gives energy for metabolism. When food runs short or work is hard, glycogen supplies the energy. Cellulose is a fibrous carbohydrate that cannot be digested; it helps regular bowel movement and prevents constipation. And proteins and fats are themselves synthesised from carbohydrates.

Eat more sugar than you need and the extra is stored in the body as fat. That can lead to obesity and sometimes even diabetes.

4. The calorie: measuring energy

The heat energy produced when one gram of food is oxidised is the food calorie. The yardstick is water: the energy needed to warm 1 gram of water by 1° Celsius is one calorie. One thousand calories make one kilocalorie, which is the same as one food calorie, and the calories of food are quoted in kilocalories. Put the steps in order.

Carbohydrate and protein give almost the same, about 4 kcal/g. Fat gives the most, 9 kcal/g.

An adult man needs food worth about 2500 kcal a day, and an adult woman about 2000 kcal.

Before the sum, get a feel for it. Drag the grams of the three components; each one's energy grows as a bar, and the day's total lines up against the daily needs of a woman and a man.

The sum is simple: grams times kcal per gram. 20 g of fat gives 20 × 9 = 180 kcal. 50 g of carbohydrate gives 50 × 4 = 200 kcal. Change the numbers yourself.

5. Digestion, assimilation, respiration

Enzymes in different parts of the digestive system break complex food into simpler substances; this is digestion. The digested food is absorbed and built into the protoplasm of body cells; this is assimilation. In respiration the chemical energy of food changes into heat and other forms of energy.

6. Check yourself

The first question is about a definition.

In the second, recall the components.

In the last, check your numbers.

The whole note on eight cards.

Source: Science, Classes 9-10 (NCTB), Chapter 1 “Healthy Life, Better Living”, section 1.1.