In its technical sense, a diet is a food schedule that represents a disciplined pattern of consumption. Diets are created or designed to achieve a particular state of health, including larger or smaller body mass, higher or lower levels of intake of particular food types, or to regulate the intake of accompanying vitamins, minerals, or other supplements to improve physical performance.

Diet has both broader and deeper meanings in its use by both the general population and athletes alike. The expression "you are what you eat" is one with which everyone can identify. Technical aspects aside, a diet is both the checklist as well as the yardstick to determine how the body's essential systems perform on the fuels provided.

The quantity of a diet and its quality are measured in different ways. Quantity is determined by the number of calories contained in the total foods consumed. In physics, a calorie is defined as the unit of measurement that represents the amount of energy required to raise the temperature of 1 gram of water 1°C; for dietary calculations, a calorie is 1 kilocalorie, or 1,000 calories. The dietary calorie is best understood with reference to what it represents. The most familiar comparison to quantify the dietary caloric measure is that 1 lb (2.2 kg) of excess fat on the human body represents 3,500 calories of either food intake or required energy expenditure. All foods are capable of being measured by their caloric value, because all foods will be converted by digestion into a form of energy, whether the substance enters the body as a carbohydrate, a protein, or a fat. When a diet is set out in writing, it will refer to both the size of the food product to be consumed, as well as its corresponding caloric value. The greater or smaller the portion of the food consumed will determine the proportionate calculation of the number of calories in the particular diet.

The number of calories represented by the diet is of importance is determining whether the amount of energy available through the diet will sustain an athlete through the workouts and competitions. If a body has too little fuel available through food consumption, it will either resort to converting fat or protein stores into energy, which are not efficient processes, or the body will simply not be able to perform as intended.

When the calories represent the quantity of the fuel available to the body, the components of the diet will represent the fuel quality: all calories, for the purpose of optimum human health and athletic performance, are not of equal value. All diets are composed of three general types of foods: carbohydrates, proteins, and fats. The proportion of each of these components in a diet is critical in the achievement of general health, as well as the specific desired benefits to enable an athlete to perform in a particular discipline that itself places specific demands on the body.

Carbohydrates are broadly understood as the fuel used to power the body, both in its muscular movements as well as its nervous system, cardiovascular system, and organ function. Carbohydrates are the compounds found in many forms of plant life that are a byproduct of photosynthesis, the reaction between sunlight and the plant structure. Carbohydrates are generically classed as sugars, and they are typically divided into three subcategories: simple sugars, or monosaccharides, of which glucose is an example, so called because they possess a simple carbon/hydrogen/oxygen structure; double sugars, or disaccharides, such as sucrose; and complex sugars, also referred to as starch, known as polysaccharides, which are stored in the body for future energy uses as glycogen in both the liver and the skeletal muscles. Glycogen, reduced to glucose, is the product used by the body to create adenosine triphosphate (ATP), the ultimate fuel product converted to muscular energy.

The most prevalent sources of carbohydrates typically found in the human diet are those derived from plant sources in their natural or harvested state, such as potatoes, grains, fruits, and vegetables, as well as those plant sources that are processed or refined into food products, such as bread, pastas, and all sugar products. In the typical diet of a healthy adult person, carbohydrates will form approximately 60-65% of the daily total caloric intake.

Proteins are nitrogen-based molecules that are closely related to the body-building compounds known as amino acids. Proteins are essential to the building, maintenance, and repair of all muscles in the body. While protein can be utilized as a source of energy, it is inferior to both carbohydrate and fat supplies in this regard. Proteins are found in a number of food sources, the best known of which are animal meats, soy beans, and its derivatives, and dairy products. The body generally requires 12-15% of its diet as proteins.

Fats are the third component of the diet structure. The term fat has a highly negative connotation in popular culture, as dietary fats are equated with the excess fatty tissue acquired in the human body when the output of calories, through exercise, is less than the caloric value of the foods consumed. The fats consumed for the purposes of diet are defined as organic compounds that are constructed in various combinations of carbon, oxygen, and hydrogen molecules. Fats are a highly concentrated and inefficient source of bodily energy that are present in numerous foods, and are subdivided into two types. Saturated fats are those that are consumed primarily through animal meats, and excess consumption of animal fats in diet will often lead to a corresponding excess of cholesterol present in the body. Cholesterol is a type of fat known as low density lipoproteins (LDLs), which in excess amounts are a known inhibitor of good cardiovascular function. Unsaturated fats are found predominately in plants and fish products. Unsaturated fats contain high density lipoproteins (HDLs), which are a key to healthy cardiovascular function.

The body extracts, or otherwise converts, some available fats into fatty acids, which play a vital role in the ability of the body to absorb and metabolize certain fat-soluble vitamins such as A and E, which are essential to healthy human function. The best known of these "healthy fats" is omega-3, which is found in salmon and tuna oils. Another form of fatty acid, trans fatty acid, or trans fat, is commonly found in fried foods made with vegetable oils and commercially prepared baked goods; trans fat has a negative effect on the cardiovascular system as it is believed to contribute to the clogging of arteries. A healthy diet, which is often referred to as a balanced diet, will not usually exceed 30% fat.

In addition to an appropriate caloric value, suitable to the energy required by a person, and a balanced diet, certain food agents are desirable additions to assist with the digestion and the processing of the food consumed. Fiber (also known as roughage) is the term used to describe the food component that is desired not for its caloric or other nutritional value, but as a digestive aid. It cannot be processed for energy by the body, and fiber therefore does not have a caloric value. Foods such as apples, beans, and corn and other plants possess high amounts of soluble fiber, which assist slowing the digestive process and permitting nutrients to be better absorbed; insoluble fibers, present in foods such wheat and oat bran, make the elimination of solid wastes from the body easier by adding bulk to the waste products.

Another essential aspect of diet that is not related to the caloric value of the food are the dietary vitamins and minerals consumed through food. As with fiber, vitamins and minerals are not a part of the energy sources, as the body does not convert them in the fashion that carbohydrates are converted. Vitamins and minerals are commonly regarded as an interchangeable nutritional package; they are separately defined components of diet, that often work together to enhance health.

Vitamins are a group of substances that are of critical importance to the body's metabolism (the creation and processing of stored energy); vitamins are also an integral part of the growth and maintenance of the musculoskeletal system, as well as the prevention of disease. There are 13 vitamins that are essential to optimal human function, each referenced by a letter: vitamin A, the vitamin B complex (a grouping of eight separate but related compounds), and vitamins C, D, E, and K. All vitamins, with the exception of D and K, are obtained through diet; vitamins D and K are the products of synthesis within the body, a process that indirectly requires proper nutrition to occur. Vitamins A, D, E, and K are fat soluble, which require free fatty acids to facilitate storage and which will be absorbed into the body systems to function as required. The remainder of the necessary vitamins is water soluble, permitting absorption directly into the bloodstream through the digestive process and the working of the small intestine. Water-soluble vitamins are not stored within the body and each must be consumed on a daily basis.

Minerals are inorganic substances found naturally in the earth; the name is derived from the ability to mine the substances underground. Minerals entering the body through foods are in some instances elements in their pure form as found in the periodic table; other minerals are elements in compound form. The most common example is table salt, or sodium chloride; sodium is the mineral required for the proper function of a number of the body's systems.

There are many minerals required to achieve optimum human function. The most important minerals are calcium (also, the most plentiful mineral in the body, essential to bones, teeth, the transmission of nerve impulses, and muscle function), sodium (which assists in the regulation of blood volume and related blood pressure), and potassium (known as an electrolyte, critical to athletic performance and essential to general body development and growth). An example of the chemical partnerships formed in the maintenance of the body is the relationship between vitamin D and calcium, which are interdependent in the formation of bones.

Mineral stores can become quickly depleted through the stresses placed upon the human systems through exercise. A reduction in mineral levels cannot be compensated by way of assistance from

The food pyramid.
internal body processes. Mineral shortages can be addressed to a significant degree with the consumption of energy drinks during competition, and by way of supplements consumed as a regular part of diet.

While the approximately 60% carbohydrate to 15% protein to 25% fat dietary ratio, together with optimum fiber, vitamin, and mineral consumption, will support a typical healthy adult, there are a multitude of dietary variations used to achieve specific athletic purposes. The low carbohydrate diets advanced for weight loss purposes and often popularized in the media are usually an unsuitable dietary basis for serious athletic training programs. Carbohydrates are the prime food source for the ultimate production of muscular energy; if the ratio of carbohydrates were significantly reduced in an athlete's diet, the body would be required to seek energy production from either proteins or fats. Neither of these groups is as efficient in the production of ATP as is carbohydrate-derived glucose.

In the specialized circumstances of elite performance, diet components can be strictly analyzed and adjusted for optimal athletic benefit. As an example, a weight training program aimed at building a greater degree of muscle mass might result in an adjustment of the amount of protein consumed. Given the body of each individual athlete may pose variations from the expected dietary requirements, two athletes on the same training program may have slightly different patterns of food consumption.

Dietary supplements are commonly consumed by athletes to ensure that the proper daily nutritional requirements are met. Numerous investigations into the relative ability of the body to absorb vitamins and minerals from food versus pill or powdered supplements suggest that these nutrients are best ingested from food; for water-soluble nutrients, it is very difficult to ingest sufficient amounts in any fashion that poses a danger of overload, as the excess amount is passed out of the system. There is a risk presented from the over-consumption of fat-soluble nutrients: excess consumption of vitamin D may lead to the formation of calcium-composed kidney stones.

SEE ALSO Carbohydrates; Fat intake; Protein supplements; Sport nutrition.