Nutrition is the science of the nutrients in food. Nutrients provide energy, are necessary for the growth and repair of tissues and regulate body processes. So to live, we must not only eat but cat the right things.
The first requirement of the body is calorics. Food is measured in units of heat called calorics. One caloric equals the amount of heat needed to raise one gram of water one degree Centigrade. In food values this means that one gram of carbohydrate – sugar and starch – produces
3.7 calorics; one gram of protein – meat, fish, eggs and milk – produces
1 calories; and one gram of fat – butter, oil and lard – produces 9.3 calories.
Fats are a necessary part of a normal diet.
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They act as lubricants, fuel and as insula-tion against the cold. Without them the body would be unable to utilise fat- soluble vitamins.
Animal fats are valuable sources of Vitamins A and D. Both animal and vegetable fats should be included in the diet, and, depending on the age, weight and occupation of the person, the intake of fats should be no more than about 25 per cent-of the daily intake of calories.
Proteins are an essential part of a diet because they include many elements which the body requires for growing and rebuilding.
Proteins are complex combinations of amino acids. Some of the amino acids which the body does not require can be converted into those that it does. But there are some which cannot be made by the body and which must be included in the diet. The protein foods which contain these essential amino acids in the largest proportions are meat, fish, eggs, milk and cheese.
The body cannot store large quantities of amino acids, so ideally you should eat a mixture of protein foods at each meal.
For example, it is better to eat a mixture of meat, cereal and vegetables at one meal than to eat meat for one meal and cereal for the next.
For vegetarians to get enough of the essential amino acids they must eat not only a wide variety, but also a large quantity, of protein foods (including nuts and legumes).
Approximately 15 per cent of the daily intake of calories should be proteins.
Carbohydrates include sugars and starches. They contribute heat and energy and when absorbed in a greater quantity then the body requires, they are converted into body fat.
In the Western world, the consumption of sweets, sweet drinks and starch forms such a large part of the diet, particularly of children, that there is some danger that these children may be overfed and yet be undernourished.
Generally speaking, carbohydrates should form no more than 60 per cent of the daily intake of calories., The most important minerals are calcium, phosphorous and iron. See MINERALS.
Enzymes are organic catalysts – sub-stances which induce change without being affected themselves and which do not form part of the resultant product. For example, vitamins, acting as enzymes, oxidise carbohydrates turning them into sugars for absorption by the body.
Vitamins are organic substances found in minute quantities in foods. Fat-soluble vitamins are A, D, E and K, and Vitamin C and the vitamins of the B group are water-soluble.
Vitamins are supplied by a varied diet of raw and freshly cooked foods.