Nutrition is the provision, to cells and organisms, of the materials necessary (in the form of food) to support life. Many common health problems can be prevented or alleviated with good nutrition.
An organism's diet is what it eats. Dietitians are health professionals who specialize in human nutrition, meal planning, economics, preparation, and so on. They are trained to provide safe, evidence-based dietary advice and management to individuals (in health and disease), as well as to institutions.
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.
Contents [hide]
1 Overview
2 Nutrients
2.1 Carbohydrates
2.2 Protein
2.3 Fat
2.4 Vitamins
2.5 Minerals
2.6 Fiber
2.7 Water
2.8 Antioxidants
2.8.1 Phytochemicals
2.9 Intestinal bacterial flora
3 Sports nutrition
3.1 Protein
3.2 Water and Salts
3.3 Carbohydrates
4 Longevity
4.1 Whole plant food diet
4.2 The French "paradox"
5 Mental agility
6 Mental disorders
7 Processed foods
8 Advice and guidance
8.1 Governmental policies
8.2 Teaching
9 History
9.1 Antiquity through 1900
9.2 1900 through 1941
9.3 Recent
10 See also
11 Further reading
12 References
13 External links
13.1 Databases and search engines
13.2 Governmental agencies and intergovernmental bodies
[edit] Overview
Nutritional science investigates the metabolic and physiological responses of the body to diet. With advances in the fields of molecular biology, biochemistry, and genetics, the study of nutrition is increasingly concerned with metabolism and metabolic pathways, the sequences of biochemical steps through which the many substances of living things change from one form to another.
The human body contains chemical compounds, such as water, carbohydrates (sugar, starch, and fiber), amino acids (in proteins), fatty acids (in lipids), and nucleic acids (DNA/RNA). These compounds, in turn, consist of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, calcium, iron, zinc, magnesium, manganese, and so on. All of these chemical compounds and elements occur in various forms and combinations (e.g. hormones/vitamins, phospholipids, hydroxyapatite), both in the human body and in organisms (e.g. plants, animals) that humans eat.
The human body consists of elements and compounds ingested, digested, absorbed, and circulated through the bloodstream. Except in the unborn fetus, it is the digestive system which carries out the first steps in feeding the cells of the body. In a typical adult, about seven liters of digestive juices enter the lumen of the digestive tract. They break chemical bonds in ingested molecules and modulate their conformations and energy states. Though some molecules are absorbed into the bloodstream unchanged, digestive processes release them from the matrix of foods in which they occur. Unabsorbed matter is excreted in the feces.
Studies of nutritional status must take into account the state of the body before and after experiments, as well as the chemical composition of the diet and the products of excretion. Comparing the food to the waste can help determine the specific compounds and elements absorbed in the body. Their effects may only be discernible after an extended period of time, during which all food and waste must be analyzed. The number of variables involved in such experiments is high, making nutritional studies time-consuming and expensive, which explains why the science of human nutrition is still slowly evolving.
In general, eating a wide variety of fresh, whole (unprocessed), foods has proven favourable compared to monotonous diets based on processed foods. In particular, the consumption of whole plant foods slows digestion and provides higher amounts, and a more favourable balance, of essential nutrients per Calorie, resulting in better management of cell growth, maintenance, and mitosis (cell division), as well as better regulation of appetite and blood sugar. Regularly scheduled meals (every few hours) have also proven more wholesome than infrequent, haphazard ones.
[edit] Nutrients
Main article: Nutrient
There are seven major classes of nutrients: carbohydrates, fats, proteins, vitamins, minerals, fiber, and water.
The molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. They provide energy, which is measured in kilocalories, often called "Calories" and written with a capital C to distinguish them from calories.
Proteins contain nitrogen atoms in addition to carbon, hydrogen, and oxygen. They do contain chemical energy (contributing Calories to the diet), but more importantly, they consist of the nitrogen-containing amino acids, which fulfill many roles other than energy metabolism, and when they are used as fuel, getting rid of the nitrogen places a burden on the kidneys.
Vitamins, minerals, fiber, and water do not provide energy, but are necessary for other reasons.
It is important to consume all seven daily to maintain health.[citation needed]
Poor health can be caused by an imbalance of nutrients, whether an excess or a deficiency.
According to the United Nations World Health Organization (WHO: 1996), the real challenge in developing nations today, more than starvation, is malnutrition--the lack of nutrients necessary for growth and the maintenance of vital functions.
[edit] Carbohydrates
Main article: Carbohydrate
kcal/gram: 4[1]
Carbohydrates may be classified as monosaccharides, disaccharides, or polysaccharides by the number of sugar units they contain. Monosaccharides contain 1 sugar unit, disaccharides contain 2, and polysaccharides contain 3 or more. Polysaccharides are often referred to as complex carbohydrates because they are long chains of sugar units, whereas monosaccharides and disaccharides are simple carbohydrates. The difference is important to nutritionists because complex carbohydrates take longer to metabolize since their sugar units are processed one-by-one off the ends of the chains. Simple carbohydrates are metabolized quickly and thus raise blood sugar levels more quickly resulting in rapid increases in blood insulin levels.
Several lines of evidence indicate lifestyle-induced hyperinsulinemia and reduced insulin function (i.e. insulin resistance) as a decisive factor in many disease states. For example, hyperinsulinemia and insulin resistance are strongly linked to chronic inflammation, which in turn is strongly linked to a variety of adverse developments such as arterial microinjuries and clot formation
