Nutrients are certain chemical compounds that are present in foods and that fulfill one or more of the following functions:
- Supply energy for body functions.
- Build and replace cells that make up body tissues.
- Regulate body processes.
There are six categories of nutrients:
- Carbohydrates
- Fats
- Proteins
- Vitamins
- Minerals
- Water
CALORIES
The calorie is a unit of measurement of energy. It is defined as the amount of heat needed to raise the temperature of 1 kilogram of water by 1°C. Remember that one of the functions of nutrients is to supply energy to the body.
The calorie is used to measure how much energy certain foods supply for these functions. In our overfed society, calories have come to be viewed as something to be avoided. Nevertheless, without sufficient food energy, we could not live.
Carbohydrates, proteins, and fats can be used by the body to supply energy.
1 gram of carbohydrate supplies 4 calories
1 gram of protein supplies 4 calories
1 gram of fat supplies 9 calories
There is a direct connection between calorie intake, physical activity, and weight gain. Simply put, if you consume more calories than you burn, you gain weight. If you consume fewer calories than you burn, you lose weight. All the diet schemes and fashions in the world-at least the ones that are medically sound-can be reduced to this.
In other words, losing weight is possible only by eating fewer calories, by burning more calories through exercise, or, preferably, by both.
In order to lose weight while maintaining good nutrition and health, one should avoid empty calories as much as possible and eat primarily foods of high nutrient density.Empty calorie foods are those that provide few nutrients per calorie. Refined sugars and starches are examples of empty calories. Foods of high nutrient density are those that have relatively many nutrients per calorie. Fruits,vegetables,and whole grains are examples of foods with high nutrient density.
KINDS OF NUTRIENTS AND THEIR IMPORTANCE
Each of the nutrients listed has certain characteristics and functions in the body.These are discussed below in general terms.. Many fad diets emphasize either the good or the bad qualities of one particular nutrient.
For example,a particular weight loss diet may advise eating mostly protein foods and eliminating carbohydrates as much as possible. However, because all nutrients are essential, such diets can lead to nutritional imbalances. Thus, it is necessary to understand the function and importance of all nutrients.
The amount of each nutrient needed daily varies from person to person, depending on such factors as age, sex, general health, and level of activity.
Carbohydrates
Carbohydrates are compounds consisting of carbon, hydrogen, and oxygen atoms bound together in chains of varying lengths.
Sugars are simple carbohydrates. Simple sugars, such as glucose, are small compounds containing 6 carbon atoms.Table sugar, or sucrose, is a larger sugar molecule with 12 carbon atoms. Sugars are found in sweets and, to a lesser extent, in fruits and vegetables.
Starches are complex carbohydrates consisting of long chains of simple sugars bound together.They are found in such foods as grains, bread,peas and beans, and many vegetables and fruits. Carbohydrates are the body’s most important source of food energy. Fats and proteins can also be burned for energy, but the body uses carbohydrates first. If no carbohydrates are available,the body then burns fat.
However, if fats are burned with no carbohydrates present, toxic compounds called ketone bodies are produced. If too many ketone bodies accumulate, a condition called ketosis develops, and the blood becomes unable to carry oxygen properly.The result can be fatal. Thus, one of the important functions of carbohydrates is to help the body burn fat properly. About 50 to 100 grams of carbohydrates are needed every day to prevent ketosis.
Most authorities believe that complex carbohydrates, especially those from whole grains and unrefined foods, are better for you than simple carbohydrates.This is partly because starchy foods also have many other nutrients,while sweets have few other nutrients.
Also, there is some evidence that a lot of sugar in the diet may contribute to heart and circulatory diseases. Simple sugars and refined starches are primary sources of empty calories.
Another reason that carbohydrates from whole grains and unrefined foods are preferable to those from refined sugars and starches is that these unrefined foods are sources of fiber. The term fiber refers to a group of carbohydrates that cannot be absorbed and used by the body. Therefore,fiber supplies no food energy. However,it is important for the proper functioning of the intestinal tract and the elimination of body waste.
In addition, there is evidence that sufficient dietary fiber helps prevent some kinds of cancers and helps decrease cholesterol in the blood. Fruits and vegetables, especially raw,and whole grains supply dietary fiber.
Fiber can be classified as either soluble or insoluble.Soluble fiber absorbs water and forms a kind of gel. It is found inside and between plant cells.Insoluble fiber also absorbs water, but less, and forms bulk in the intestines. It is found in cell walls and other structural parts of plants.
Fats
Fats supply energy to the body in highly concentrated form. Also, some fatty acids are necessary for regulating certain body functions.Third, fats act as carriers of fat-soluble vitamins (vitamins A,D, E, and K). Because of these important functions, it is necessary to have some fats in the diet.
Fats may be classified as saturated, monounsaturated, or polyunsaturated. These terms reflect chemical differences in the composition of fats. Cooks do not need to know the chemical structure of fats, but they should understand their nutritional characteristics and the foods in which they are found. Many foods contain a combination of these three types,with one type predominating.
Saturated fats are solid at room temperature. Animal products-meats, poultry, fish, eggs, dairy products-and solid shortenings are the major source of saturated fats.Tropical oils such as coconut oil and palm kernel oil are also rich in saturated fats.
Health experts believe these fats contribute significantly to heart disease and other health problems.Polyunsaturated fats and monounsaturated fats are liquid at room temperature.
Although too much of any kind of fat is unhealthy,these fats are considered more healthful than saturated fats.Polyunsaturated fats are found in vegetable oils such as corn oil, safflower oil,sunflower oil,and cottonseed oil.High levels of monounsaturated fats are found in olive oil and canola oil.
Both kinds of unsaturated fats are also found in other plant products as well,including whole grains,nuts,and some fruits and vegetables.
One group of saturated fats of special concern is trans fats.These fats occur naturally in small amounts only. Most of the trans fats in our diets are from manufactured fats subjected to a process called hydrogenation. Hydrogenated fats are fats that are changed from liquid to solid by adding hydrogen atoms to the fat molecules.
This is the process used to make products such as solid shortening and margarine.Trans fats are of concern because they limit the body’s ability to rid itself of cholesterol that builds up on the walls of arteries
Fats are members of a group of compounds called lipids. Another lipid found in the body is cholesterol, a fatty substance that has been closely linked with heart disease because it collects on the walls of arteries and blocks the flow of blood to the heart and other vital organs.
It is found only in animal products and is especially high in egg yolks, butterfat, and organ meats such as liver and brains. In addition, the human body can manufacture its own cholesterol, so not all the cholesterol in the blood is necessarily from foods.
Although some cholesterol is necessary for body functions,it is not considered a nutrient because the body is able to manufacture all the cholesterol it needs. Experts generally agree it is best to keep the cholesterol in the diet as low as possible.
Recent research has suggested that monounsaturated fat may actually lower the levels of the most harmful kinds of cholesterol in the body.This may explain the relatively low incidence of heart disease in Mediterranean regions, where olive oil is the most widely used fat.This research has helped popularize the use of olive oil in other parts of the world, especially in North America.
Remember,however, that too much fat of any kind is bad for the health. Do not make the mistake of thinking that monounsaturated fats are good for you and can be used in excess.