Main article: Nutrient

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.

The macronutrients (excluding fiber and water) provide energy, which is measured in kilocalories, often called "Calories" and written with a capital C to distinguish them from small calories. Carbohydrates and proteins provide four (4) Calories of energy per gram, while fats provide nine (9) Calories per gram.[1] 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, 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. Similar to fatty acids, certain amino acids are essential.

Other micronutrients not categorized above include antioxidants and phytochemicals.

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, whether an excess or a deficiency.


Main article: Carbohydrate

Calories/gram: 4

A pack of toasted bread is a cheap, high nutrient food source (which also has a long shelf life) and may be used (as can dehulled rice) to combat famines.
A pack of toasted bread is a cheap, high nutrient food source (which also has a long shelf life) and may be used (as can dehulled rice) to combat famines.

Carbohydrates may be classified as monosaccharides, disaccharides, or polysaccharides by the number of monomer (sugar) units they contain. They are found in foods as rice, noodles and other grain-based products, potatoes, ... 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 simpler. The difference is important because complex carbohydrates take longer to digest and absorb since their sugar units are processed one-by-one off the ends of the chains; the spike in blood sugar levels caused by substantial amounts of simple surgars is thought to be at least part of the cause of increased heart and vascular disease associated with high simple sugar consumption. Simple carbohydrates are absorbed quickly and thus raise blood sugar levels more quickly.


Main article: Fat

Calories/gram: 9

Fats are composed of fatty acids (long carbon/hydrogen chains) bonded to a glycerol; they are typically found as triglycerides (three fatty acids attached to one glycerol backbone). Certain fatty acids are essential. Fats may be classified as saturated or unsaturated. Saturated fats have all of their carbon atoms bonded to hydrogen atoms, whereas unsaturated fats have some of their carbon atoms double-bonded in place of a hydrogen atom. In humans, multiple studies have shown that unsaturated fats are to be preferred for health reasons, particularly mono-unsaturated fats. Saturated fats, typically from animal sources, are next, while 'trans' fats are to be avoided; they have been banned in several locations (eg, New York City). Saturated and trans fats are typically solid at room temperature (such as butter or lard), while unsaturated fats are typically liquids (such as olive oil or flaxseed oil). Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Trans fats are saturated fats but are typically created from unsaturated fat by adding the extra hydrogen atoms in an industrial process called hydrogenation; they are also called hydrogenated fat. They are very rare in nature, but have properties useful in the food processing industry.[citation needed]

Essential fatty acids

Main article: Essential fatty acids

Most fatty acids are non-essential, meaning the body can produce them as needed from other fats and some energy. However, in humans, at least two fatty acids are essential and must be consumed in the diet. An appropriate balance of essential fatty acids - omega-3 and omega-6 fatty acids - has been discovered to be important in reducing risk of some chronic diseases and conditions. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins which have uses throughout the human body; they are in some respects, hormones. The omega-3 eicosapentaenoic acid (EPA) (which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (LNA), or taken in through marine food sources), serves as a building block for series 3 prostaglandins (e.g. weakly-inflammation PGE3). The omega-6 dihomo-gamma-linolenic acid (DGLA) serves as a building block for series 1 prostaglandins (e.g. anti-inflammatory PGE1), whereas arachidonic acid (AA) serves as a building block for series 2 prostaglandins (e.g. pro-inflammatory PGE 2). Both DGLA and AA can be made from the omega-6 linoleic acid (LA) in the human body, or can be taken in directly through food. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins, which partly explains the importance of omega-3/omega-6 balance for cardiovascular health. In industrialised societies, people typically consume large amounts of processed vegetable oils that have reduced amounts of the essential fatty acids along with a too high ratio of omega-6 fatty acids relative to omega-3 fatty acids.

The conversion rate of omega-6 DGLA to AA largely determines the production of the respective prostaglandins PGE1 and PGE2. Omega-3 EPA prevents AA from being released from membranes, thereby skewing prostaglandin balance away from pro-inflammatory PGE2 made from AA toward anti-inflammatory PGE1 made from DGLA. Moreover, the conversion (desaturation) of DGLA to AA is controlled by the enzyme delta-5-desaturase, which in turn is controlled by hormones such as insulin (up-regulation) and glucagon (down-regulation). Because the amount and type of glucose and starch )plus some amino acid types) in food affect insulin, glucagon and other hormones, not only the amount of omega-3 versus omega-6 eaten but also the general composition of the diet, are implicated in general health regarding the essential fatty acids, inflammation (e.g. immune function) and mitosis (i.e. cell division).

Good sources of essential fatty acids include: fish, flax seed oils, hemp seeds adn oils, soy beans, pumpkin seeds, sunflower seeds, and walnuts.


Main article: Dietary fiber

Calories/gram: 0

Dietary fiber consists mainly of cellulose, a large carbohydrate polymer, that is indigestible because humans do not have enzymes to digest it. There are two subcategories, soluble and insoluble fiber. The first means fiber which absorbs water, the second does not. Whole grains, fruits (especially plums, prunes, and figs), and vegetables are rich in dietary fiber. It provides bulk to the intestinal contents and stimulates peristalsis (rhythmic muscular contractions passing along the digestive tract). Consequently, a lack of dietary fiber in the diet tends toward constipation. There is also some evidence that dietary fiber is helpful in other ways, eg, reducing the incidence of some cancers.


Main article: Protein in nutrition

Calories/gram: 4

Most meats such as chicken contain all the essential amino acids needed for humans.
Most meats such as chicken contain all the essential amino acids needed for humans.

Proteins are the basis of animal body structures (eg, muscles, skin, hair etc.). They are composed of amino acids, sometimes many thousands, which are characterized by inclusion of nitrogen and sometimes sulphur. The body requires amino acids to produce new body protein (protein retention) and to replace damaged proteins (maintenance). Amino acids not needed are discarded, typically in the urine. In animals, amino acid requirements are classified in terms of essential (an animal cannot produce them internally) and non-essential (the animal can produce them from other nitrogen containing compounds) amino acids. Humans use about 20 amino acids, and about ten are essential in this sense. Consuming a diet that contains adequate amounts of essential (but also non-essential) amino acids is particularly important for growing pregnant, nursing, or injured animals, all of whom have a particularly high requirement. Protein nuitrition which contains the essential amino acids is a complete protenin source, one missing one or more is called incomplete. It's possible to combine two incomplete protein sources (eg, rice and beans) to make a complete protein source. Dietary sources of protein include meats, tofu and other soy-products, eggs, grains, legumes, and dairy products such as milk and cheese. A few amino acids from protein can be converted into glucose and used for fuel through a process called gluconeogenesis. The remaining amino acids are discarded.


Main article: Dietary mineral

Calories/gram: 0

Dietary minerals are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen which are present in common organic molecules. The term "mineral" is archaic, since the intent of the definition is to describe ions, not chemical compounds or actual minerals. Some dietitians recommend that these heavier elements should be supplied by ingesting specific foods (that are enriched in the element(s) of interest), compounds, and sometimes including even minerals, such as calcium carbonate. Sometimes these "minerals" come from natural sources such as ground oyster shells. Sometimes minerals are added to the diet separately from food, such as mineral supplements, the most famous being iodine in "iodized salt".


A variety of elements are required to support the biochemical processes, many play a role as electrolytes or in a structural role.[2] In human nutrition, the dietary bulk "mineral elements" (RDA > 200 mg/day) are in alphabetical order (parenthetical comments on folk medicine perspective):

  • Calcium (for muscle and digestive system health, builds bone, neutralizes acidity, clears toxins, helps blood stream)
  • Chloride
  • Magnesium required for processing ATP and related reactions (health, builds bone, causes strong peristalsis, increases flexibility, increases alkalinity)
  • Phosphorus required component of bones (see apatite) and energy processing and many other functions (bone mineralization)[3]
  • Potassium required electrolyte (heart and nerves health)
  • Sodium electrolyte
  • Sulfur for three essential amino acids and many proteins and cofactors (skin, hair, nails, liver, and pancreas health)

Trace minerals

A variety of elements are required in trace amounts, unusually because they play a role in catalysis in enzymes.[4] Some trace mineral elements (RDA <>

Iodine is required in larger quantities than the other trace minerals in this list and is sometimes classified with the bulk minerals. Sodium is not generally found in dietary supplements, despite being needed in large quantities, because the ion is very common in food.


Main article: Vitamin

Calories/gram: 0

Mineral and/or vitamin deficiency or excess may result in disease conditions such as goitre, scurvy, osteoporosis, impaired immune system, disorders of cell metabolism, certain forms of cancer, symptoms of premature aging, and poor psychological health (including eating disorders), among many others.[5]

As of 2005, twelve vitamins and about the same number of minerals are recognized as "essential nutrients", meaning that they must be consumed and absorbed—or, in the case of vitamin D, alternatively synthesized in the skin via UVB radiation to prevent deficiency symptoms and possibly death. Certain vitamin-like substances found in foods, such as carnitine, have also been found essential to survival and health, but these are not strictly "essential" to eat because the human body can produce them from other compounds. Moreover, thousands of different phytochemicals have recently been discovered in food (particularly in fresh vegetables), which may have desirable properties including antioxidant activity (see below). Other essential nutrients include essential amino acids, choline and the essential fatty acids.


A manual water pump in China
A manual water pump in China
Main article: Drinking water

Calories/gram: 0

About 70% of the non-fat mass of the human body is made of water[citation needed]. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors[citation needed]. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

It is not clear how much water intake is needed by healthy people, although some experts assert that 8–10 glasses of water (approximately 2 liters) daily is the minimum to maintain proper hydration.[6] The notion that a person should consume eight glasses of water per day cannot be traced back to a scientific source.[7] The effect of water intake on weight loss and on constipation is also still unclear.[8] Original recommendation for water intake in 1945 by the Food and Nutrition Board of the National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."[9] The latest dietary reference intake report by the United States National Research Council in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men.[10] Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. According to the Institute of Medicine—who recommend that, on average, women consume 2.2 litres and men 3.0 litres—this is recommended to be 2.4 litres (approx. 9 cups) for pregnant women and 3 litres (approx. 12.5 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing.[11]

For those who have healthy kidneys, it is rather difficult to drink too much water[citation needed], but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which can be fatal. In particular large amounts of de-ionized water are dangerous.

Normally, about 20 percent of water intake comes in food, while the rest comes from drinking water and assorted beverages (caffeinated included). Water is excreted from the body in multiple forms; including urine and feces, sweating, and by water vapor in the exhaled breath.

Other nutrients

Calories/gram: 0

Other micronutrients include antioxidants and phytochemicals. These substances are generally more recent discoveries which: have not yet been recognized as vitamins; are still under investigation; or contribute to health but are not necessary for life. Phytochemicals may act as antioxidants, but not all phytochemicals are antioxidants.

[edit] Antioxidants

Main article: Antioxidant

Antioxidants are a recent discovery. As cellular metabolism/energy production requires oxygen, potentially damaging (e.g. mutation causing) compounds known as free radicals can form. Most of these are oxidixers 9ie, acceptors of electrons) and some react very strongly. For normal cellular maintenance, growth, and division, these free radicals must be sufficiently neutralized by antioxidant compounds. Some are produced by the human body with adequate precursors (glutathione, Vitamin C and those that the body cannot produce may only be obtained through the diet through direct sources (Vitamin C in humans, Vitamin A, Vitamin K) or produced by the body from other compounds (Beta-carotene converted to Vitamin A by the body, Vitamin D synthesized from cholesterol by sunlight). Phytochemicals (Section Below) and their subgroup polyphenols are the majority of antioxidants; about 4,000 are known. Different antioxidants are now known to function in a cooperative network, e.g. vitamin C can reactivate free radical-containing glutathione or vitamin E by accepting the free radical itself, and so on. Some antioxidants are more effective than others at neutralizing different free radicals. Some cannot neutralize certain free radicals. Some cannot be present in certain areas of free radical development (Vitamin A is fat-soluble and protects fat areas, Vitamin C is water soluble and protects those areas). When interacting with a free radical, some antioxidants produce a different free radical compound that is less dangerous or more dangerous than the previous compound. Having a variety of antioxidants allows any byproducts to be safely dealt with by more efficient antioxidants in neutralizing a free radical's butterfly effect.


Main article: Phytochemical

A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals. These nutrients are typically found in edible plants, especially colorful fruits and vegetables, but also other organisms including seafood, algae, and fungi. The effects of phytochemicals increasingly survive rigorous testing by prominent health organizations. One of the principal classes of phytochemicals are polyphenol antioxidants, chemicals which are known to provide certain health benefits to the cardiovascular system and immune system. These chemicals are known to down-regulate the formation of reactive oxygen species, key chemicals in cardiovascular disease.

Perhaps the most rigorously tested phytochemical is zeaxanthin, a yellow-pigmented carotenoid present in many yellow and orange fruits and vegetables. Repeated studies have shown a strong correlation between ingestion of zeaxanthin and the prevention and treatment of age-related macular degeneration (AMD).[12] Less rigorous studies have proposed a correlation between zeaxanthin intake and cataracts.[13] A second carotenoid, lutein, has also been shown to lower the risk of contracting AMD. Both compounds have been observed to collect in the retina when ingested orally, and they serve to protect the rods and cones against the destructive effects of light.

Another caretenoid, beta-cryptoxanthin, appears to protect against chronic joint inflammatory diseases, such as arthritis. While the association between serum blood levels of beta-cryptoxanthin and substantially decreased joint disease has been established, neither a convincing mechanism for such protection nor a cause-and-effect have been rigorously studied.[14] Similarly, a red phytochemical, lycopene, has substantial credible evidence of negative association with development of prostate cancer.

The correlations between the ingestion of some phytochemicals and the prevention of disease are, in some cases, enormous in magnitude.

Even when the evidence is obtained, translating it to practical dietary advice can be difficult and counter-intuitive. Lutein, for example, occurs in many yellow and orange fruits and vegetables and protects the eyes against various diseases. However, it does not protect the eye nearly as well as zeaxanthin, and the presence of lutein in the retina will prevent zeaxanthin uptake. Additionally, evidence has shown that the lutein present in egg yolk is more readily absorbed than the lutein from vegetable sources, possibly because of fat solubility.[15] At the most basic level, the question "should you eat eggs?" is complex to the point of dismay, including misperceptions about the health effects of cholesterol in egg yolk, and its saturated fat content.

As another example, lycopene is prevalent in tomatoes (and actually is the chemical that gives tomatoes their red color). It is more highly concentrated, however, in processed tomato products such as commercial pasta sauce, or tomato soup, than in fresh "healthy" tomatoes. Yet, such sauces tend to have high amounts of salt, sugar, other substances a person may wish or even need to avoid.

The following table presents phytochemical groups and common sources, arranged by family:

Family Sources Possible Benefits
flavonoids berries, herbs, vegetables, wine, grapes, tea general antioxidant, oxidation of LDLs, prevention of arteriosclerosis and heart disease
isoflavones (phytoestrogens) soy, red clover, kudzu root general antioxidant, prevention of arteriosclerosis and heart disease, easing symptoms of menopause, cancer prevention[16]
isothiocyanates cruciferous vegetables cancer prevention
monoterpenes citrus peels, essential oils, herbs, spices, green plants, atmosphere[17] cancer prevention, treating gallstones
organosulfur compounds chives, garlic, onions cancer prevention, lowered LDLs, assistance to the immune system
saponins beans, cereals, herbs Hypercholesterolemia, Hyperglycemia, Antioxidant, cancer prevention,


capsaicinoids all capiscum (chile) peppers topical pain relief, cancer prevention, cancer cell apoptosis

Intestinal bacterial flora

Main article: Gut flora

It is now also known that animal intestines contain a large population of gut flora. In humans, these include species such as Bacteroides, L. acidophilus and E. coli, among many others. They are essential to digestion, and are also affected by the food we eat. Bacteria in the gut perform many important functions for humans, including breaking down and aiding in the absorption of otherwise indigestible food; stimulating cell growth; repressing the growth of harmful bacteria, training the immune system to respond only to pathogens; producing vitamin B12, and defending against some diseases.

Balanced diet

Balanced diet is a diet which consists of all the essential nutrients in a required proportion .

Junk food

Junk food is a slang name for food items containing limited nutritional value. It includes food high in salts, fats, sugar, calories, and low nutrient content.