Nutrition

Nutrition is the process by which an organism obtains and uses raw materials from its environment in order to stay alive. Autotrophs, like plants, are able to make their own nutrients, while heterotrophs, like animals, must ingest or eat them. Nutritional needs of plants and animals are different. These needs may vary considerably for animals according to their age, sex, level of activity, and reproductive status.

Nutrients are any substances that are taken in by a living thing in order to survive or to sustain its life. All living things must take in nutrients from their environment in order to grow and repair themselves and to provide the energy they need. This process of taking in nutrients and using them is called nutrition.

AUTOTROPHS

Plants and animals not only have different nutritional requirements, but they obtain their nutrients in different ways. Plants are called autotrophs because they produce many of their own nutrition requirements by photosynthesis. Photosynthesis is the chemical conversion of the Sun's light into simple food chemicals. A plant makes its own nutrients from inorganic materials like nitrogen (gas), carbon dioxide (gas), and sunlight. The basic elements that a plant needs are mostly in the soil in which they grow. Elements required in large amounts are called macronutrients. These macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorous, potassium, calcium, and magnesium. Plants also require smaller amounts of micronutrients such as chlorine, iron, boron, manganese, zinc, copper, molybdenum, and nickel. Plants, or autotrophs, are considered the "primary producers" in the food chain (the series of stages energy goes through in the form of food) because all other life depends on them directly or indirectly.

HETEROTROPHS

Heterotrophs include humans and other animals. Heterotrophs cannot make organic material the way plants can. Instead, they must obtain their nutrients from the food they eat. Heterotrophs are divided into herbivores that eat plants, carnivores that eat other animals, and omnivores who eat both plants and animals. Humans are omnivores and must obtain their nutrients from plants and animals. Like plants, the nutrients humans take in are also divided into macronutrients and micronutrients.

Macronutrients are substances humans need in large amounts, like carbohydrates, proteins, and fats. All three of these essential nutrients are large, complex molecules that must be digested, or broken down, into smaller units so they can be absorbed or taken into the body's cells. Micronutrients are substances like vitamins and minerals that people need in much smaller amounts. However, just because micronutrients are not needed in great quantity does not mean that they are not essential to the proper functioning of the body. Vitamins are especially important because they help enzymes (proteins that control the rate of chemical changes) regulate chemical reactions and are not generally stored by the body. This means that vitamins must be obtained by one's diet.

For all living things, food is a key to life since it contains the raw materials, or nutrients, needed to stay alive. Food performs three functions for animals. It acts as fuel for all of the various reactions that take place in the human body, and it provides energy to move about. Food also provides the organic raw materials for the body to make new structures and to repair others. Finally, food contains the nutrients that animals cannot make for themselves. A good example are the much-needed ten "essential amino acids" that the body cannot make on its own, but must be obtained through food.

MALNUTRITION

The condition known as malnutrition literally means "bad nutrition," and an organism is described as malnourished when it is not getting enough of one or more nutrients. The lack of enough carbohydrates and fats means that eventually, the body will start to consume its own proteins. This only happens when a person is actually starving, and it leads to a wasting away that eventually proves fatal.

VARYING NUTRITIONAL NEEDS

The absence of an important vitamin usually leads to a specific deficiency disease, and the lack of a needed mineral also can lead to serious conditions. For humans, a diet that supplies the proper amount of nutrients is said to be "balanced," but a person's nutritional needs vary greatly according to their stage in life. During infancy, a person's total energy requirements are the highest. Later in childhood, growth is rapid, and protein intake should be fairly high to develop new tissue. During adolescence, growth spurts also occur, which make impressive nutritional demands. In adulthood, growth has stopped and nutritional requirements are less, although they are still very important to maintaining good health.

A person's level of activity also affects their nutritional needs, and a pregnant woman or an athlete both have different nutritional needs compared to an inactive senior citizen. Although the nutrient amounts taken in depends on these and other variables, a general rule of thumb would be that carbohydrates should provide half of the total energy intake; fats should make up about one third; and protein should comprise the remainder.

[See alsoAmino Acid; Carbohydrate; Lipids; Malnutrition; Protein; Vitamin ]