Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with good nutrition.Poor diet can have an injurious impact on health, causing deficiency diseases such as scurvy, beriberi, and kwashiorkor; health-threatening conditions like obesity and metabolic syndrome, and such common chronic systemic diseases as cardiovascular disease, diabetes, and osteoporosis. There are seven major classes of nutrients: carbohydrates (saccharides), fats (triglycerides), fiber (cellulose), minerals, proteins, vitamins, and water.These nutrient classes can be generally grouped into the categories of macronutrients (needed in relatively large amounts), and micronutrients (needed in smaller quantities). The macronutrients are carbohydrates, fats, fiber, proteins and water. The other nutrient classes are micronutrients and also include antioxidants and phytochemicals.

    The macronutrients (excluding fiber and water) provide energy, which is measured in kilocalories. Carbohydrates and proteins provide four (4) Calories of energy per gram, while fats provide nine (9) Calories per gram. Vitamins, minerals, fiber, and water do not provide energy, but are necessary for other reasons.

   Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates may be simple monomers (glucose, fructose, galactose), or large polymers polysaccharides (starch). Fats are triglycerides, made of various fatty acid monomers bound to glycerol. Some fatty acids are essential, but not all. Protein molecules contain nitrogen atoms in addition to the elements of carbohydrates and fats. The nitrogen-containing monomers of protein, called amino acids, Similar to fatty acids, certain amino acids are essential.Most foods contain a mix of some or all of the nutrient classes. Some nutrients are required on a regular basis, while others are needed less frequently. Poor health can be caused by an imbalance of nutrients.

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