kilocalories (often called "Calories" and written with a capital 'C' to distinguish them from little 'c' calories). Carbohydrates and proteins provide 17 kJ approximately Human nutrition deals with the provision of essential nutrients in food that are necessary to support human life and good health. Poor nutrition is a chronic problem often linked to poverty, food security, or a poor understanding of nutritional requirements. Malnutrition and its consequences are large contributors to deaths, physical deformities, and disabilities worldwide. Good nutrition is neces Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so. However, in humans, at least two fatty acids are essential and must be included in the diet. An appropriate balance of essential fatty acids—omega-3 and omega-6 fatty acids—seems also important for health, although definitive experimental demonstration has been elusive. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. The omega-3 eicosapentaenoic acid (EPA), which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (ALA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g., weakly inflammatory 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. In industrialized societies, people typically consume Carbohydrates, fats, and proteins are macronutrients, and provide energy. Water and fiber are macronutrients, but do not provide energy. The micronutrients are minerals and vitamins. The macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built), and energy. Some Fats are triglycerides, made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids, some of which are essential in the sense that humans cannot make them internally. Some of the amino acids can be converted (with the expenditure of energy) to glucose and can be used for energy production just as ordinary glucose, in a process known as gluconeogenesis. An appropriate balance of essential fatty acids—omega-3 and omega-6 fatty acids—seems also important for health, although definitive experimental demonstration has been elusive. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. The omega-3 eicosapentaenoic acid (EPA), which can be made in the human body from the omega-3 essential fatty acid alpha-linolenic acid (ALA), or taken in through marine food sources, serves as a building block for series 3 prostaglandins (e.g., weakly inflammatory PGE3). Like all carbohydrates, when fiber is digested, it can produce four calories (kilocalories) of energy per gram, but in most circumstances, it accounts for less than that because of its limited absorption and digestibility. The two subcategories are insoluble and soluble fiber. Insoluble dietary fiber Includes cellulose, a large carbohydrate polymer that is indigestible by humans, because humans do not have the required enzymes to break it down, and the human digestive system does not harbor enough of the types of microbes that can do so. Soluble dietary fiber Comprises a variety of oligosaccharides, waxes, esters, and other carbohydrates that dissolve or gelatinize in water. Many of these soluble fibers can be fermented or partially fermented by microbes in the human digestive system to produce short-chain fatty acids which are absorbed and therefore introduce some caloric content. Whole grains, beans, and other legumes, fruits (especially plums, prunes, and figs), and vegetables are good sources of dietary fiber. Fiber has three primary mechanisms, which in general determine their health impact: bulking, viscosity and fermentation. Iron required for many enzymes, and for hemoglobin and some other proteins Manganese (processing of oxygen) Molybdenum required for xanthine oxidase and related oxidases Selenium required for peroxidase (antioxidant proteins) Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase ==== Ultratrace minerals ==== Ultratrace minerals are an as yet unproven aspect of human nutrition, and may be required at amounts measured in very low ranges of μg/day. Many ultratrace elements have been suggested as essential, but such claims have usually not been confirmed. (Many animal species can synthesize vitamin C, but humans cannot.) Certain vitamin-like compounds that are recommended in the diet, such as carnitine, are thought useful for survival and health, but these are not "essential" dietary nutrients because the human body has some capacity to 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); experimental demonstration has been suggestive but inconclusive.

Diet and cholesterol gallstones. A multicenter study. In France, changes in the incidence of gallstones during the 20 years following World War II paralleled the changes in total calories, protein and lipid of the diet. The incidence of gallstones in autopsy statistics has been compared to the diets in different countries: France, India, Japan, Portugal, South Africa, Sweden and Uganda. Low calorie, low protein, low lipid intake and vegetable diet are associated with a low incidence of gallstones. A positive correlation between calorie intake and gallstones incidence was found at necropsy for calorie intakes lower than 3,000 kcal. In countries with high calorie, high protein and high lipid intakes, such a correlation was not found. These results suggest that a hypocaloric diet associated with a low intake of fat and protein mostly of vegetable origin, is protective against cholelithiasis. Published in Digestion (1978)

These analyses indicated that higher intakes of protein of vegetal origin, total carbohydrate, starch, and crude fiber are associated with less atherosclerotic lesion involvement. For other components (total calories, total protein, animal protein, total fat, animal or vegetal fat, saturated or unsaturated fatty acids, total sugars, and cholesterol), there were no indications that the daily consumption was related to atherosclerotic lesions found at autopsy. When the diet-lesion relationships were examined on the basis of nutrient-to-calorie ratios, starch and vegetal protein were associated with less atherosclerotic lesion involvement in the coronaries, while animal protein and fat, regardless of source, were associated with greater atherosclerotic lesion involvement. These results suggest that, in general, the consumption of more foods of vegetal origin may be related to a lesser degree of atherosclerotic involvement. Published in Journal of the American Dietetic Association (1976)