Did you ever wonder where your energy comes from, and how it is derived from the foods you eat? The truth is, we get energy from carbohydrates, fats and protein, and when you go on restrictive diets, you short-change some systems in your body, and short-change your health.
Humans require food substances to supply the components necessary to build tissues, to repair tissues as they wear out and die, to keep the body in good working condition, and to supply fuel for energy. A well-balanced diet is one that provides an adequate amount of each of the classes of nutrients each day, furnishing at the same time an adequate but not excessive number of calories for the body’s energy needs. Children require relatively larger amounts of nutrients and calories because of their rapid growth. The foods required for proper nutrition fall roughly into three major groups: proteins, carbohydrates, and fats.
Carbohydrates are the human body’s key source of energy, providing 4 calories of energy per gram. When carbohydrates are broken down by the body, the sugar glucose is produced; glucose is critical to help maintain tissue protein, metabolize fat, and fuel the central nervous system.
Glucose is absorbed into the bloodstream through the intestinal wall. Some of this glucose goes straight to work in our brain cells and red blood cells, while the rest makes its way to the liver and muscles, where it is stored as glycogen (animal starch), and to fat cells where it is stored as fat. Glycogen is the body’s auxiliary energy source, tapped and converted back into glucose when we need more energy.
Starches and sugars are the major carbohydrates. Common starch foods include whole-grain breads and cereals, pasta, corn, beans, peas, and potatoes. Naturally occurring sugars are found in fruits and many vegetables; milk products; and honey, maple sugar, and sugar cane. Foods that contain starches and naturally occurring sugars are referred to as complex carbohydrates, because their molecular complexity requires our bodies to break them down into a simpler form to obtain the much-needed fuel — glucose. Our bodies digest and absorb complex carbohydrates at a rate that helps maintain the healthful levels of glucose already in the blood.
In contrast, simple sugars, refined from naturally occurring sugars and added to processed foods, require little digestion and are quickly absorbed by the body, triggering an unhealthy chain of events. The body’s rapid absorption of simple sugars elevates the levels of glucose in the blood, which triggers the release of the hormone, insulin. Insulin reins in the body’s rising glucose levels, but at a price: Glucose levels may fall so low within one to two hours after eating foods high in simple sugars, such as candy, that the body responds by releasing chemicals known as anti-insulin hormones. This surge in chemicals, the aftermath of eating a candy bar, can leave a person feeling irritable and nervous.
Many processed foods not only contain high levels of added simple sugars, they also tend to be high in fat and lacking in the vitamins and minerals found naturally in complex carbohydrates. Nutritionists often refer to such processed foods as junk foods and say that they provide only empty calories, meaning they are loaded with calories from sugars and fats but lack the essential nutrients our bodies need. Nutritionists caution that most Americans need to eat more complex carbohydrates. Foods rich in complex carbohydrates, which provide vitamins, minerals, some protein, and dietary fiber and are an abundant energy source, should make up roughly 50 percent of our daily calories.
Fats, which provide 9 calories of energy per gram, are the most concentrated of the energy-producing nutrients, so our bodies need only very small amounts. Fats play an important role in building the membranes that surround our cells and in helping blood to clot. Once digested and absorbed, fats help the body absorb certain vitamins. Fat stored in the body cushions vital organs and protects us from extreme cold and heat.
Fat consists of fatty acids attached to a substance called glycerol. Dietary fats are classified as saturated, monounsaturated, and polyunsaturated according to the structure of their fatty acids. Animal fats – from eggs, dairy products, and meats – are high in saturated fats and cholesterol, a chemical substance found in all animal fat. Vegetable fats – found, for example, in avocados, olives, some nuts, and certain vegetable oils – are rich in monounsaturated and polyunsaturated fat.
High intake of saturated fats can be unhealthy. While we need cholesterol, we do not need it in our diet. The liver, and to a lesser extent the small intestine, manufacture all the cholesterol we require. When we eat cholesterol from foods that contain saturated fatty acids, we increase the level of a cholesterol-carrying substance in our blood that harms our health. Saturated fatty acids – found in foods ranging from beef to ice cream, to mozzarella cheese to doughnuts – should make up no more than 10 percent of a person’s total calorie intake each day. Excessive saturated fats are considered harmful to the heart and blood vessels because they are thought to increase the level of LDLs (the ‘bad’ cholesterol), and decrease the level of HDLs (the good cholesterol).
Monounsaturated fats – found in olive, canola, and peanut oils – appear to have the best effect on blood cholesterol, decreasing the level of LDLs and increasing the level of HDL’s. Polyunsaturated fats – found in margarine and sunflower, soybean, corn, and safflower oils – are considered more healthful than saturated fats. However, if consumed in excess (more than 10% of daily calories), they can decrease the blood levels of HDLs. Choosing a diet that is low in fat and cholesterol is critical to maintaining health and reducing the risk of life-threatening disease. (9)
Protein: Although protein provides 4 calories of energy per gram, the body uses protein for energy only if carbohydrate and fat intake is insufficient. When tapped as an energy source, protein is diverted from the many critical functions it performs for our bodies.
Dietary proteins are powerful compounds that build and repair body tissues, from hair and fingernails to muscles. In addition to maintaining the body’s structure, proteins speed up chemical reactions in the body, serve as chemical messengers, fight infection, and transport oxygen from the lungs to the body’s tissues.
Proteins are made up of smaller units called amino acids. Of the more than 20 amino acids our bodies require, eight or nine cannot be made by the body in sufficient quantities to maintain health. These amino acids are considered essential and must be obtained from food. When we eat food high in proteins, the digestive tract breaks this dietary protein into amino acids. Absorbed into the bloodstream and sent to the cells that need them, amino acids then recombine into the functional proteins our bodies need.
Animal proteins, found in such food as eggs, milk, meat, fish, and poultry, are considered complete proteins because they contain all of the essential amino acids our bodies need. Plant proteins, found in vegetables, grains, and beans, lack one or more of the essential amino acids. However, plant proteins can be combined in the diet to provide all of the essential amino acids. A good example is rice and beans. Each of these foods lacks one or more essential amino acids, but the amino acids missing in rice are found in the beans, and vice versa.
Recommended protein daily intake by experts:
- A three month old infant: 13 g
- 4 year old child 22 g
- A healthy woman 45 g
- A man of average size 57 g
- A pregnant woman 55 g
- A breast-feeding mother 65 g
Illness and stress place an enormous demand on the body as it builds tissue or fights infection, and these conditions require an increase in protein consumption.
Good nutrition is reflected not only in the growth, function and energy of the body but also in its appearance. The eyes, skin, hair, and teeth indicate whether body nourishment is good or poor. Poor nutrition may result from excesses in the diet as well as deficiencies; excess of certain vitamins or minerals can produce potentially lethal disease states, and excess of carbohydrates or fat can result in obesity.