Baskadia

Nutrition begins with food. Nutrition is the process by which the body nourishes itself by transforming food into energy and body tissues. The science of nutrition concerns everything the body does with food to carry on its functions. Food provides essential substances called nutrients. The body needs these nutrients to help it make energy; to grow, repair, and maintain its tissues; and to keep its different systems working smoothly. Nutrition is important for all organisms. However, this article will focus on nutrition as it applies to the human body.

The term nutrition can also refer to the quality of someone’s food choices, or diet. A balanced diet is one in which foods eaten on a regular basis provide all the nutrients needed in the right amounts. A balanced diet has many benefits. It can help people feel and look their best. It can also help them stay energetic and healthy, both in the short term and later in life.

CALORIES AND ENERGY BALANCE

The body’s most basic need is for energy. The energy in food is measured in units called kilocalories (commonly shortened to “calories”). One kilocalorie is the amount of heat energy needed to raise the temperature of 1 kilogram (2.2 pounds) of water 1° C (1.8° F). (More precisely, it is the energy required to raise that water from 14.5° C to 15.5° C at one atmosphere of pressure.)

Three major types of nutrients supply the body with energy, or calories: carbohydrates, proteins, and fats. One gram (0.035 ounce) of either carbohydrate or protein provides four calories. Fat is a more-concentrated source of energy, with each gram providing nine calories. Water, vitamins, and minerals supply no energy in and of themselves, though the body uses many of them in energy-releasing processes.

The body needs the energy in food to do everything from blinking an eye to running a race. It also needs energy to perform such essential functions as breathing, maintaining body temperature, growing new cells, and even digesting food. The total number of calories needed each day depends on many factors, including a person’s age, sex, weight, and especially level of activity. For example, a woman who weighs about 120 pounds (55 kilograms) might expend 1,850 calories on a day when she is fairly sedentary but may use more than 3,000 calories on a very active day.

If a person takes in more food than is required to meet the body’s needs, the excess calories are eventually converted to fat—a form of stored energy found mostly within adipose tissue. That causes weight gain. Eating too little causes weight loss over time, because the body must use stored fat for energy. One pound (0.5 kilogram) of adipose tissue is equal to about 3,500 calories.

Maintaining a healthy weight is a balancing act. Food provides energy, and physical activity uses up energy. If weight loss is advisable, experts recommend both reducing one’s daily calorie intake and getting more exercise.

NUTRIENTS

The nutrients are divided into six major types: carbohydrates, proteins, fats, vitamins, minerals, and water. Each nutrient performs specific functions to keep the body healthy. All the nutrients work together to contribute to good health.

CARBOHYDRATES

The body’s main source of energy is carbohydrates, which include starches, sugars, and dietary fiber. The body breaks down starches and sugars into the simple sugar glucose, the fuel used by red blood cells. Glucose is also the main energy source for the brain and nervous system and can be used by muscles and other body cells. Fiber does not provide energy.

Starches are complex carbohydrates. They are found in dry beans and peas, such as kidney beans, pinto beans, soybeans, chickpeas, lentils, and split peas; grains and grain products, such as breads and cereals; potatoes; and other vegetables. These foods can also be good sources of proteins, vitamins, minerals, and dietary fiber.

Sugars, or simple carbohydrates, also are a natural part of many foods. There are several types. Fructose, for example, is found in fruits, maltose in grain products, and lactose in milk. These sugars are part of foods that also provide other nutrients.

Refined sugars are sugars that are removed from plants and used as sweeteners, or added sugars. Sucrose, or table sugar, is produced commercially from sugarcane and sugar beets and is used to sweeten many foods, such as candy and desserts. Other sweeteners include high-fructose corn syrup, a refined sugar that is commonly added to soft drinks and packaged baked goods; honey; maple syrup; and molasses. All these sugars provide calories but little or no additional nutrients. In addition, eating large amounts of sweetened foods can lead to weight gain and tooth decay (see dentistry).

Dietary fiber likewise provides no essential nutrients. Fiber is the structural part of plants, and the human body cannot digest it. However, eating dietary fiber is beneficial to the body in many ways. Fiber aids digestive health and may protect against certain disorders and diseases.

There are two types of fiber: insoluble (which does not dissolve in water) and soluble (which dissolves or swells in water). Insoluble fiber, or roughage, speeds the passage of food—and potentially harmful substances in food—through the intestines. This type of fiber is thought to provide protection against some gastrointestinal diseases. Good food sources include whole-grain breads and cereals, wheat bran, and vegetables. Soluble fiber can help lower the level of harmful cholesterol in the blood and limit the rise in blood sugar levels after eating. Soluble fiber is found in apples and other fruits, dry beans and peas, oats, and barley.