Components of Food — REET Notes

Components of food — an introduction

Our food is mainly made up of six kinds of nutrients — carbohydrates, protein, fat, vitamins, mineral salts, and water; besides these, roughage (dietary fibre) is also an important part of food. These are grouped into two big categories — macronutrients (carbohydrates, protein, fat), which the body needs in larger amounts, and micronutrients (vitamins, minerals), which are needed in smaller amounts but are just as essential to how the body functions.

Nutrients, their sources, and functions

Matching sources to functions, in exactly this table format, is a common REET question type — so it helps to be able to name at least one everyday source and one main function for each of the six nutrients listed here.

Energy-giving, body-building, and protective food

Textbooks also classify food into three groups by function. Energy-giving food — such as carbohydrate- and fat-rich food — gives the body the energy to work. Body-building food — such as protein-rich food (pulses, milk, egg) — helps with growth and repair. Protective food — such as vitamin- and mineral-rich fruit and vegetables — protects the body from diseases and keeps its normal functions regulated. This three-way grouping by function sits alongside, rather than instead of, the six-nutrient classification in the table above — the same carbohydrate, protein, vitamin, and mineral that appear there are simply being grouped here by what job they do in the body.

The importance of a balanced diet

A balanced diet is one where all the nutrients — carbohydrates, protein, fat, vitamins, mineral salts, roughage, and water — are present in the right, appropriate amounts, which can vary based on a person's age, sex, physical activity, and health status. A long-term shortage of any nutrient can lead to malnutrition and specific deficiency diseases, while eating more than necessary can lead to problems like obesity — so maintaining balance matters, and the right amount for one person is not automatically the right amount for another.

Testing food for nutrients (food tests)

Starch test

Turns blue-black on adding iodine solution, which shows starch is present

Protein test

Turns purple/pink on adding copper sulphate and caustic soda solution (the biuret test), which shows protein is present

Fat test

Leaves a translucent, greasy stain when rubbed on paper, which stays even after the paper dries

Water test

Steam coming out when any fresh food is heated shows the presence of water in that food

Loss of nutrients during cooking, and malnutrition

Overcooking food for too long, reheating it repeatedly, or peeling and soaking vegetables in water for a long time can destroy several water-soluble vitamins (such as vitamin C and some B-group vitamins). So not cutting vegetables more than needed, cooking them covered and in less water, and eating soon after cooking all help preserve nutrients that would otherwise be lost in the cooking process itself.

When a diet lacks necessary nutrients for a long time, it's called malnutrition, which affects not just physical growth but also weakens disease resistance. On the other hand, eating more food than necessary (especially food rich in fat and sugar) can lead to problems like obesity — detailed information on diseases caused by specific nutrient deficiencies is covered in the 'Vitamins and Deficiency Diseases' topic.

For growing children and adolescents, having variety in food is especially important, so that all nutrients — grains, pulses, milk, seasonal fruit, and green vegetables — are available in balanced amounts. Schemes like the mid-day meal in schools also aim to regularly give children nutritious, balanced food, so their physical and mental growth is better supported, which is exactly the same balanced-diet principle described above, applied at school scale.

How to teach this to students

Practice questions

Frequently asked questions

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