Why do we eat?
Food gives us energy to work and play, materials to grow and repair the body, and substances that protect us from disease. The useful substances in food are called nutrients.
The major nutrients are carbohydrates, proteins, fats, vitamins and minerals. Food also contains dietary fibre (roughage) and water, which are not nutrients in the strict sense but are essential for good health.
The nutrients and their jobs
Component | Main job | Rich sources |
|---|---|---|
Carbohydrates | give energy | rice, wheat, potato, sugar, maize |
Fats | give energy (more than carbohydrates per gram) and store it | ghee, butter, oil, nuts |
Proteins | build and repair the body; needed for growth | pulses (dal), milk, paneer, eggs, fish, meat, soybean |
Vitamins | protect against disease; keep eyes, bones, teeth and gums healthy | fruits, vegetables, milk |
Minerals | build bones and teeth, make blood, keep the body working | milk, green leafy vegetables, salt, jaggery |
Dietary fibre | helps the body get rid of undigested food | whole grains, fruits, vegetables, pulses |
Water | carries nutrients, removes wastes through urine and sweat, controls body temperature | water, fruits, buttermilk |
Carbohydrates and fats are called energy-giving foods, proteins body-building foods, and vitamins and minerals protective foods.
Testing food for nutrients
You can detect some nutrients with simple tests in the laboratory.
Starch: add 2 or 3 drops of dilute iodine solution to the food. A blue-black colour shows starch is present.
Protein: mix the food with water, add 2 drops of copper sulphate solution and 10 drops of caustic soda (sodium hydroxide) solution, and shake. A violet colour shows protein is present.
Fat: rub the food on a piece of paper. An oily patch that lets light through shows fat is present.
Vitamins and minerals
Vitamin or mineral | Needed for | Deficiency disease or symptom |
|---|---|---|
Vitamin A | healthy eyes and skin | night blindness (poor vision in dim light) |
Vitamin B1 | nerves and heart | beriberi (weak muscles, little energy) |
Vitamin C | healthy gums; fighting infection | scurvy (bleeding gums, slow healing) |
Vitamin D | strong bones (helps absorb calcium) | rickets (soft, bent bones) |
Calcium | bones and teeth | weak bones, tooth decay |
Iodine | the thyroid gland | goitre (swollen neck) |
Iron | making blood | anaemia (tiredness, pale skin) |
Our skin makes vitamin D when it is exposed to sunlight. Vitamin C is easily destroyed by heat, so cooking vegetables for too long reduces it.
A balanced diet
A balanced diet contains every nutrient, plus fibre and water, in the right amounts for the body's needs. A meal of chapati, dal, a green vegetable, curd and a fruit is a good example.
How much food we need depends on age, sex and how active we are. A labourer doing heavy physical work needs more energy-giving food than someone who sits at a desk all day.
Too little or too much
Deficiency diseases happen when a nutrient is missing from the diet for a long time. They can be prevented by eating a balanced diet.
Eating too much fatty food can lead to obesity, which increases the risk of heart disease and diabetes.
Cooking also matters. Washing vegetables before cutting them, rather than after, and not throwing away the water in which rice or dal was cooked help to save nutrients.
Summary
Carbohydrates and fats give energy, proteins build the body, and vitamins and minerals protect it.
Iodine turns starch blue-black; copper sulphate with caustic soda turns protein violet; fat leaves an oily patch on paper.
A balanced diet has all nutrients in the right amounts; a long-term lack causes deficiency diseases.