apple nutritionBasic human Nutrition requires carbohydrates, fats, proteins (amino acids) and vitamins. Inorganic chemical compounds such as dietary minerals may also be considered nutrients and essential to good health. A nutrient is essential to an organism if it cannot be synthesized by the organism in sufficient quantities and must be obtained from an external source.

Nutrients needed in relatively large quantities are called macronutrients and those needed in relatively small quantities are called micronutrients. Food provides nutrients from six broad classes: proteins, fats, carbohydrates, vitamins, dietary minerals, and water. Carbohydrates are metabolized to provide energy. Proteins provide amino acids, which are required for cell construction, especially for the construction of muscle cells.

Essential fatty acids are required for brain and cell membrane construction. Vitamins and trace minerals help maintain proper electrolyte balance and are required for many metabolic processes. Dietary fiber is another food component which influences health even though it is not actually absorbed into the body.

Any diet that fails to meet minimum nutritional requirements can threaten general health (and physical fitness in particular). If a person is not well enough to be active, weight loss and good quality of life will be unlikely. The National Academy of Sciences and the World Health Organization publish guidelines for dietary intakes of all known essential nutrients.

Sometimes dieters will ingest excessive amounts of vitamin and mineral supplements. While this is usually harmless, some nutrients are dangerous. Men (and women who don’t menstruate) need to be wary of iron poisoning. Retinol (oil-soluble vitamin A) is toxic in large doses.

As a general rule, most people can get the nutrition they need from foods. In any event, a multivitamin taken once a day will suffice for the majority of the population.

Weight-loss diets which manipulate the proportion of macronutrients (low-fat, low-carbohydrate, etc.) have not been found to be more effective than diets which maintain a typical mix of foods with smaller portions and perhaps some substitutions (e.g. low-fat milk, or less salad dressing). Extreme diets may, in some cases, lead to malnutrition.

The average woman 25 years of age and older should get 50 grams of protein each day, and the average man 25 years of age and older should get 63 grams of protein each day.

Protein is important because it prevents muscle tissue from breaking down and repairs all body tissues such as skin and teeth. To get adequate protein in your diet, make sure you eat 2-3 servings of meat, poultry, fish, dry beans, eggs, and nuts.

At least 100 grams of carbohydrates per day are needed to prevent fatigue and dangerous fluid imbalances. To make sure you get enough carbohydrates, eat 6-11 servings of bread, cereal, rice, and pasta.

No more than 30 percent of your calories should come from fat (avoid saturated fat).

Mammalian development is a highly regulated process and there is ample evidence that inadequate nutrition at various critical stages of development can lead to permanent long-term detrimental effects.

The mechanisms by which these effects occur are largely unknown. Some are truly genetic, reflecting genomic defects that interfere with normal nutrition during development, some are epigenetic, representing environmental effects.

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