Macronutrients

Food does much more than fill the stomach. Good nutrition keeps a person healthy and free from disease. It helps the body grow and develop, repairs cells and tissues that are damaged, gives the energy for work and play, protects the body and strengthens its power to resist disease. For this reason every person should choose nutritious food that suits their own age, weight and height.

The body does not need every nutrient in the same amount. In one day we eat hundreds of grams of rice, bread or porridge, yet some nutrients are needed in amounts smaller than a single gram. Nutrients are therefore divided into two groups by how much of them the body needs: macronutrients and micronutrients. Minerals and vitamins, which are needed in amounts of less than one gram a day, are the micronutrients. Here we study the macronutrients, the ones needed in large amounts.

There are three macronutrients:

• carbohydrate
• protein
• fat

All three can give the body energy, but each has a different main job. Carbohydrate is the chief source of energy, protein builds and repairs cells, and fat stores a large amount of energy. Each of them is divided further into kinds of its own. The chart below shows the whole family in one place.

A student who eats rice in the morning can run, play and study all day at school. Most of that energy comes from carbohydrate. Carbohydrate is the most important source of energy for the body. It gives the body the heat and the strength it needs. Inside the body, one gram of carbohydrate gives four calories of energy.

Carbohydrate is made of three elements joined together: carbon, hydrogen and oxygen. The body changes the carbohydrate we eat into glucose, fructose and galactose, because only in these forms can it be absorbed. If the body receives more carbohydrate than it needs for energy, the extra is changed into a fat called triglyceride and stored in different parts of the body. As this stored fat builds up, a person starts to look fat.

Carbohydrate supplies sugar, starch and fibre in different amounts. The carbohydrate in food is divided into two kinds: simple carbohydrate and complex carbohydrate.

Simple carbohydrates include monosaccharides and disaccharides. Glucose is a monosaccharide, while sucrose, maltose and lactose are disaccharides. Honey, sugar, milk, sugarcane and the juice of sweet fruits are sources of simple carbohydrate. It dissolves easily in water and is absorbed quickly by the body, so the energy it gives does not last long. After a glass of sweet juice you feel lively at once, but you soon feel hungry and tired again.

In complex carbohydrate the sugar molecules are joined tightly to one another. It is found in cereals, rice, wheat, millet, pulses and vegetables. It breaks down slowly in the stomach and intestines and takes time to digest, so the energy it gives lasts a long time. A farmer who eats millet porridge or rice and lentils in the morning can keep working in the field until afternoon for exactly this reason. Complex carbohydrate is considered good for health.

Carbohydrate is the nutrient we eat most of in our daily meals. Its sources can be put into three groups:

• Cereals: bread, rice, maize, barley, wheat and so on.
• Vegetables that grow under the soil: potato, sweet potato, taro, yam and so on.
• Other sources: chocolate, sugar, sugarcane, honey, jam and so on.

Carbohydrate does these jobs in the body:

• It gives the body the energy it needs.
• It protects children from malnutrition.
• It keeps the skin soft, smooth and healthy.
• It helps the body digest protein and other foods.
• It helps protein to be stored, because when enough carbohydrate is present the body does not have to burn protein for energy.

The cell is the smallest unit of the human body. When a child grows taller, a wound heals or a muscle gets stronger, new cells are being made. Protein is what builds cells and makes them grow and develop. A complete protein molecule is made mainly of carbon, hydrogen, nitrogen and oxygen. Nitrogen, which carbohydrate does not contain, is what marks protein out.

When the body lacks carbohydrate and fat, protein supplies energy instead. Protein also helps in digesting food and helps the body make its many kinds of hormones and enzymes.

A protein is made of amino acids joined one after another, like beads threaded on a necklace. The protein food we eat is broken into amino acids during digestion, and only then can the body take it in. Some amino acids come from food, while others are made naturally inside the body. When children do not get enough protein they suffer from a disease called kwashiorkor.

Amino acids are divided into two kinds according to whether the body can make them itself.

If essential amino acids are lacking, both physical and mental growth are held back. Examples are valine, histidine and leucine.

Examples are proline, serine and cystine.

Protein comes from both animals and plants. A person who does not eat meat can still get enough protein from beans, pulses and lentils.

• Animal sources: fish, meat, liver, eggs, milk, cheese, butter and so on.
• Plant sources: soybeans, chickpeas, peas, beans, groundnuts, cowpeas, lentils, cashews and so on.

Protein does these jobs in the body:

• It makes the body grow and develop, and repairs it.
• It gives the body the power to fight disease.
• It helps keep acids and alkalis in the body in balance.
• It protects children from malnutrition.
• It gives the body emergency energy when carbohydrate and fat are not available.

Fat is another nutrient the body needs. One gram of carbohydrate gives four calories of energy, but one gram of fat gives nine. So a spoonful of ghee carries more than twice the energy of the same weight of sugar. Fat is stored easily in the body, and when food runs short the body draws on this store for energy.

Fat also helps the body use its other nutrients, and it is needed to absorb the vitamins that dissolve only in fat. If fat is lacking for a long time, the body becomes dry, the skin itches and the person feels weak.

Fat is usually divided into three kinds: simple lipid, compound lipid and essential lipid. Lipid is the scientific name for a fat.

Because simple lipids contain little cholesterol, they are used a great deal, for example in milk, butter, cheese, coconut oil and mustard oil. Simple lipids are of two types, saturated fat and unsaturated fat. Put a jar of ghee and a bottle of mustard oil side by side on a cold winter morning and you can see the difference for yourself.

Unsaturated fats such as mustard oil, linseed oil and soybean oil are good for health.

Phospholipids, glycolipids and lipoproteins are compound lipids. Phospholipids are found in the different organs and cells of the human body. Lipoproteins are made by the liver, and they contain cholesterol and triglyceride. These fats are essential for running the body's activities, but too much of them in the blood harms health.

The essential lipids are linolenic acid, known as omega 3 fat, and linoleic acid, known as omega 6 fat. Children need them for physical growth and development, and everyone needs them for healthy skin and a healthy heart. Fish oil, soybean oil and sissoo seed oil are sources of essential lipids.

• Animal sources: fish, meat, milk, cheese, butter and so on.
• Plant sources: soybeans, mustard seed, coconut, sesame, linseed, sissoo seed and so on.

Fat does these jobs in the body:

• It keeps the body warm.
• It stores the fat soluble vitamins A, D, E and K.
• It makes food tasty.
• It keeps the skin soft and smooth.
• It protects the main organs of the body: the heart, the kidneys and the eyes.

The table below brings together how much of each macronutrient is needed every day, which local foods supply it, and what happens when it is lacking.

Reading the table carefully, a woman who has just given birth needs the most carbohydrate and protein. Her body has to rebuild its own strength after the birth and also produce milk for the baby. Look at protein: 29 grams for a child, 55 grams for an adult and 100 grams for a new mother, which is almost twice what an ordinary adult needs. The amounts for fat are the smallest in the table, because a little fat already gives a lot of energy.