Three of the six components give calories: carbohydrate, protein and fat. The book gives them three sections one after another, and each follows the same shape: what it is made of, its kinds, where it comes from, what it does, and what happens when there is too little or too much. Read together, the comparison is the lesson.
1. The same weight, different energy
Start with the most useful number in the section. Carbohydrate and protein each give about 4 kilocalories a gram, and fat about 9. Weight for weight, fat gives more than twice as much. Move the three sliders and watch.
the columnsmove the three sliders
From grams to kilocalories
2. Carbohydrate
Carbohydrate is made of carbon, hydrogen and oxygen, and in it the hydrogen and the oxygen stand in the same two to one as in water. The name comes from just that: carbon and water, carbohydrate.
The division is not by taste but by how many units a molecule holds. One unit makes a monosaccharide, two a disaccharide, and many a polysaccharide. Which is why starch and cellulose are carbohydrates without being sweet at all.
sort themnot by the name but by the number of units
The three classes of carbohydrate
Pick up a chip, then drop it in a bin. The question is not whether it is sweet but how many units it holds.
Right. Next one.
Not there. What is in the blood and in grapes has one unit; the starch of rice and potato has many.
All nine. The rule is easy: they all end in -ose, and the division goes by the count of units. And notice that cellulose is a carbohydrate which people cannot digest at all; that is the roughage of a later section.
Carbohydrate has one job and it is the largest one: to be the body's chief fuel and the readiest to use. What is spare is stored in the liver and the muscles as glycogen, and beyond that it is turned into fat and stored so.
3. Protein
To the carbon, hydrogen and oxygen protein adds nitrogen, and by the book's figure protein is about 16 per cent nitrogen. That nitrogen is what sets it apart from the other two. Its building unit is the amino acid.
Some amino acids the body cannot make for itself and must take from food; these are called essential. Out of that comes the idea of supplementary protein, which is the finest thing in this section.
overlappress the three buttons
Rice and lentils make a whole protein
In the rice: a great deal of carbohydrate, and some protein as well. But one essential amino acid falls short in it, so on rice alone the body cannot use all the protein it gets.
In the lentils: a good deal of protein, and what fell short in the rice is here in plenty. But another essential amino acid falls short in the lentils instead.
Taken together: the lentils make up what the rice lacks and the rice what the lentils lack. What the two give between them does very nearly the work of protein from an animal. That is what supplementary protein means, and it is why rice and lentils have been the staple here for a thousand years.
Which two amino acids they are is not named here, the book's wording not having been checked. The argument stands without the names.
Out of that comes the division in two. Protein from animals, from fish, meat, eggs and milk, generally holds every essential amino acid, and may be called whole protein. Protein from plants generally lacks one or another. But combined, plant sources give a whole protein too, and that matters, because protein from animals is not within every household's reach every day.
The work of protein is not to give energy, or not first. Its work is to build new cells and tissue, to make good wear, to grow, to make the enzymes and the hormones, and to make the antibodies that resist disease. The body burns protein only when the carbohydrate has run out.
where to find ittap a food
Where the protein is
From an animal, and whole. Nearly every essential amino acid is in it, which is why it is often taken as the standard for protein. The yolk carries fat and vitamins A and D besides.
From an animal, and whole. With unsaturated fat besides, which is what makes hilsa so oily. And small fish eaten whole give calcium from the bones.
From an animal, and whole. And with it lactose, fat, calcium and water: five components in one food.
From a plant, and not whole. One essential amino acid falls short. Taken with rice or bread the shortfall is made up; that is supplementary protein.
From a plant, and an exception. A plant source that holds very nearly every essential amino acid, so it is reckoned close to a whole protein.
From a plant, and not whole. With a good deal of fat alongside the protein, so the calories come well from it too.
Chiefly carbohydrate. There is a little protein in it too, with one essential amino acid short. With lentils that shortfall is made up.
From an animal, whole, and concentrated. With the water taken out, the same weight carries more protein than fresh fish. How it is preserved comes in the section on keeping food.
All eight. And remember that a whole protein is not a costly one; it only means that every essential amino acid is there at once. Sources that are not whole become so when they are combined.
Calling soyabean an exception among plant sources is general nutrition and not this book's. Whole and not whole are used here for the sake of plain speaking.
4. Fat
In the book's words, fat is made of fatty acids together with glycerol. Some twenty kinds of fatty acid are found in food, and it is their shape that settles whether a fat stands solid at room temperature or runs.
two layersdrag the handle
Solid or liquid, and why
The difference is one thing: whether there is a double bond in the chain. A double bond puts a bend in it, and bent chains cannot pack closely against one another, so the stuff stays liquid. Straight chains pack close, and it is solid. Saturated fat is found in the fat of fish and meat, in ghee and in butter; unsaturated fat in mustard, soyabean and sesame. The test can be made in any kitchen: look at what a bottle of coconut oil does on a cold morning.
Fat has four jobs, and the last is the least known. About 9 kilocalories a gram, the most energy of any of them. Keeping the skin in good order. Resisting the diseases of the skin. And helping vitamins A, D, E and K to be absorbed; with no fat at all in the food, those four are not properly absorbed.
Too little may bring eczema, dry skin and loss of weight; too much makes the circulation of the blood harder and the body readier to fall ill. Both are facts, and both are matters of proportion.
check yourself
One question
Which element sets protein apart from the other two that give energy?
Carbon is in all three, so it separates nothing.
Oxygen too is in all three.
Right. Carbohydrate and fat are both built of carbon, hydrogen and oxygen. Protein adds nitrogen to those three, and by the book's figure it is about 16 per cent nitrogen. That nitrogen is the amino part of an amino acid.
Hydrogen is in all three; in carbohydrate it even stands two to one with the oxygen.
check yourself
Another question
Which sugar is chiefly in honey?
Glucose lives in grapes and in the blood.
Right. Fructose is the chief sugar of honey and of ripe fruit, and it is a monosaccharide, a single unit. Glucose is in grapes and in the blood, sucrose in cane and molasses, and lactose only in milk.
Sucrose is the sugar of cane, of sugar and of molasses, and it has two units.
Lactose is found only in milk.
check yourself
Last question
Someone's food has no oil or fat at all. Carbohydrate and protein are enough, and there are vegetables. What trouble may still follow?
The absorbing of carbohydrate does not depend on fat.
Right. Those four dissolve in fat, which is to say they pass from the gut into the blood only in it. With no fat in the food, the vitamin A in the greens is there and the body cannot take all of it up. It is why a little oil goes into cooked greens: as much for the absorbing as for the taste.
Protein gives its energy without any fat, about 4 kcal a gram.
A shortage of water has nothing to do with fat.
At a glance
Carbohydrate. Carbon, hydrogen and oxygen; three classes, mono, di and poly; the chief fuel, about 4 kcal a gram. What is spare is stored as glycogen.
Protein. With nitrogen, about 16 per cent; the amino acid is its unit; its work is building, repair, enzymes, hormones and antibodies. Rice and lentils together make a supplementary protein.
Fat. Fatty acids and glycerol; saturated solid, unsaturated liquid; about 9 kcal a gram; and it helps A, D, E and K to be absorbed.
If your body or your eating is worrying you, talk to an older person at home or to a teacher at school; if it is needed they will take you to a doctor.
Source: Science, Classes 9-10 (NCTB), Chapter 1 “A better way of living”, sections 1.1.1 to 1.1.3. The figures for energy in a gram are rounded and kept the same right through the chapter.