Three kinds of function
Scientists group the jobs of food into three levels:
- Nutritional function (primary): giving the body the nutrients it needs.
- Sensory function (secondary): colour, smell, taste, texture. It makes food enjoyable.
- Body-regulating function (tertiary): helping the body defend itself and work well, beyond basic nutrients.
A nutrient is a useful substance in food, like protein or vitamin C.
Nutritional function: energy, growth and protection
The nutritional function has three parts:
- Energy-giving foods: carbohydrates (rice, wheat, sugar) and fats (oil, butter). Fat gives about 9 kcal per gram; carbohydrate and protein give about 4 kcal per gram.
- Body-building foods: proteins (dal, egg, milk, fish) build new cells for growth and repair worn-out ones. Calcium builds bones.
- Protective and regulating foods: vitamins and minerals in fruits, vegetables and milk. They help the body fight germs and control body processes, like iron in blood and iodine for the thyroid.
Water is needed too: it carries nutrients and keeps body temperature steady.
Sensory function: why taste matters
We eat with eyes, nose and tongue first. A bright colour, a good smell and a crisp bite make us want the food. They also make the mouth and stomach ready: when we smell something nice, saliva and digestive juices start flowing.
If food is dull or smells bad, we eat less and may not get enough nutrients. Cultures also use food for festivals and sharing, which makes meals a joy.
Body-regulating function and functional foods
Some food parts are not nutrients, yet they help health:
- Dietary fibre (whole grains, vegetables) keeps the gut moving and slows sugar rising in blood.
- Antioxidants (berries, green tea) help protect cells from damage.
- Probiotics (curd) are friendly bacteria that support the gut.
Foods sold for these extra benefits are called functional foods. They are not medicine and cannot replace a balanced diet.
Try it: the tiffin audit
Look at your tiffin or dinner. Write the food names. Next to each, write E (energy), G (growth) or P (protection). Is any job missing? Predict, then check: most meals miss P, the fruit or vegetable.
Key formulas and definitions
- Three functions: nutritional, sensory, body-regulating
- Nutritional function: energy + growth/repair + protection/regulation
- Energy: fat ≈ 9 kcal/g; carbohydrate ≈ 4 kcal/g; protein ≈ 4 kcal/g
- Energy foods: carbohydrates, fats; Body-building: proteins; Protective: vitamins, minerals
Worked examples
1. Put each food in a job: rice, egg, orange.
Rice: energy. Egg: growth and repair (protein). Orange: protection (vitamin C).
2. Why does a smell of freshly cooked food make you hungry?
That is the sensory function. The smell tells the brain the food is good, and the mouth starts making saliva to get ready.
3. A 20 g portion of fat is eaten. How much energy does it give?
Fat gives about 9 kcal per gram. 20 × 9 = 180 kcal.
4. A meal has 50 g carbohydrate and 10 g protein. Estimate its energy.
Both give about 4 kcal/g. Carbohydrate: 50 × 4 = 200 kcal. Protein: 10 × 4 = 40 kcal. Total about 240 kcal.
5. Is curd a functional food? Why?
Yes. Besides protein and calcium, it carries probiotic bacteria that help the gut. That extra benefit makes it a functional food.
Common mistakes
- Thinking food is only for energy. Growth, protection and enjoyment matter as well.
- Saying fibre gives energy. Fibre is not digested much, but it still helps the gut.
- Believing functional foods are medicine. They support health but do not cure disease.
- Mixing up fat and carbohydrate energy: fat has more than twice the calories per gram.