Carbohydrates include sugars, starches, and fiber. Sugars are the simplest form of carbohydrate. They are made up of one or two sugar units. They taste sweet and are found in fruit, milk, and sweeteners like honey and table sugar. Starches are made of many sugar units linked together. They do not taste sweet, and are found in cereals, grains, and starchy vegetables like potatoes.
Starches and sugars are good sources of energy in the diet and provide 4 calories per gram. Most fiber is also carbohydrate. Good sources of fiber include whole grains, legumes (peas and beans), fruits, and vegetables. Fiber provides little energy to the body because it cannot be digested or absorbed. It is, however, important for the health of the gastrointestinal tract.
Lipids are commonly called fat. Fat is a concentrated source of energy in our diet and in our bodies, providing 9 calories per gram of fat. Most of the fat in our diet and in our body is in the form of triglycerides. Each triglyceride contains three fatty acids. Fatty acids are basically long, short, or medium length chains of carbon atoms.
Depending on how these carbons are linked together, fats are classified as either saturated fats or unsaturated fats. Saturated fats are usually solid at room temperature and are found mostly in animal products such as meat, milk, and butter. Unsaturated fats are found in vegetable oils and are usually liquid at room temperature. Small amounts of certain unsaturated fatty acids are essential in the diet.
Cholesterol is another type of lipid. It is found in animal foods, but not in plants. Diets high in saturated fat and cholesterol may increase the risk of heart disease. A type of unsaturated fat called trans fat should also be limited because it promotes heart disease.
Protein is needed for growth, for the maintenance and repair of body structures, and for the synthesis of regulatory molecules. It can also be broken down to provide energy (4 calories per gram of protein). Proteins are made of folded chains of units called amino acids. The number and order of amino acids in the chain determine the type of protein.
The right amounts and types of amino acids must be consumed in the diet in order to meet the body's protein needs. Animal foods such as meat, poultry, fish, eggs, and dairy products generally supply a combination of amino acids that meets human needs better than plant proteins. However, vegetarian diets that contain only plant foods such as grains, nuts, seeds, vegetables, and legumes, can also meet protein needs.
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1. Sweet potatoes and tomato paste make a delicious and healthy combination
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