Nutrition is the science that deals with nutrients and other foods substances, and with how the body assimilates them. Human beings require food to grow, reproduce, and maintain good health, without food, our bodies could not stay warm, build or repair tissue, or maintain a heartbeat. Eating the right foods can help us avoid certain diseases or recover faster when illness occurs. These and other important functions are fuelled by chemical substances in our food called nutrients; Nutrients are classified as carbohydrates, protein, fats, vitamins, minerals and water.
The extremely complex processes that nutrients undergo in the body, how they affect one another, how they are broken down and released as energy, and how they are transported and used to rebuild countless specialized tissues and sustain the overall health of the individual are understood only approximately. Nevertheless, important nutritional decisions need to be made for the health of individuals, of groups such as the very young and the aged, and of entire populations suffering from malnutrition. Nutrition guidelines are issued by the World Health Organization (WHO) and by individual countries as a guide to what constitutes a balanced diet.
When we eat a meal, nutrients are released from food through digestion. Digestion begins in the mount by the action chewing and the chemical activity of saliva, a watery fluid that contains enzymes, certain proteins that help break down food. Further digestion occurs as food travels through the stomach and the small intestine, where digestive enzymes and acids liquefy food and muscle contractions push it along the digestive tract. Nutrients are absorbed from the inside of the small intestine into the bloodstream an carried to the sites in the body where they are needed. At these sites, several chemical reactions occur that ensure the growth and function of body tissues. The parts of foods are not absorbed continue to move down the intestinal tract and are eliminated from the body as faeces.
Once digestion, carbohydrates, proteins, and fats provide the body with the energy it needs to maintain its many functions. Scientist measure this energy in kilocalories, the amount of energy needed to raise 1 kilogram of water to 1 degree Celsius. In nutrition discussions, scientists use the term calorie instead of kilocalorie as the standard unit of measure in nutrition.
Nutrients are classified as essential or non-essential. Non-essential nutrients are manufactured in the body and do not need to be obtained from food. Examples include cholesterol, a fatlike substance present in all animal cells. Essential nutrients must be obtained from food sources, because the body either does not produce them or produces them in amounts too small to maintain growth and health. Essential nutrients include water, carbohydrates, protein, fats, vitamins, and minerals.
An individual needs varying amounts of each essential nutrient, depending upon such factors as gender and age. Specific health conditions. Such as pregnancy, breast-feeding, illness, or drug use, make unusual demands on the body and increase its need for nutrients.
Dietary guidelines, which take many of these factors into account, provide general guidance in meeting daily nutritional needs.