Carbohydrates in human nutrition

Anon. (1998). Carbohydrates in Human Nutrition. FAO Food and Nutrition Paper 66. Rome FAO. 

FAO (1998). Carbohydrates in human nutrition. Food and Nutrition Papers, Rome, Chap. 1. 

Starch is the most economically important reserve polysaccharide in the plant kingdom and is in addition the major source of carbohydrates in human nutrition. In contrast to non-starch reserve polysaccharides, which are outside the cell and the plasmalemma, starch is located in the so-called plastids or in vacuoles within the plant cells [1f In seeds, the highest starch content can be found in the endosperm, whereas its content in the embryo and the pericarp is very low. In general, the starch content of seeds or fruits varies with the degree of maturation121. Starch occurs in semicrystalline form in granules. The size and the shape of the granules is dependent on the plant species and may reach about 175 mm. 

Starch is the chief storage form of carbohydrate in plants and the most important source of carbohydrate in human nutrition. A starch molecule is a polysaccharide assembled from the simple sugar glucose it can contain anywhere from five hundred to several hundred thousand glucose molecules joined by covalent bonds into a single structure. In addition to its impor-... 

FAO/WHO (1998) Carbohydrates in Human Nutrition. Report of a Joint FAO/WHO Expert Consultation, Rome 14-18 Apr. 1997, FAO Food and Nutrition paper 66, pp. 1-140. Rome FAO. 

Figure 1 Trends in energy consumption by carbohydrate food group as a percentage of total carbohydrate in developed and developing countries, obtained from food balance data in 1994. Data obtained from FAO/WHO (1998). Carbohydrates in human nutrition. Report of a joint FAO/WHO expert consultation. FAO Food and Nutrition Papers 19 66 1-140.

Fruit juice is important in human nutrition far beyond its use as a refreshing source of liquid. Many fruits contain a variety of minor ingredients, particulary vitamins and minerals, as well as carbohydrates, which are the predominant solid component. Although fruit contains small amounts of protein and fat, these are not important ingredients of juices. 

While phosphorus is related to the two bivalent cation in human nutrition as in structural formation, it is also present in the blood cells as phosphates and in protein, lipids, carbohydrates and enzymes such as ATP and ADP. The U.S. RDA for phosphorus is one gram, and orange juice and grapefruit juice may contain between 15 to 20 mg per 100 ml. 

Fats and oils have major roles in human nutrition. They are concentrated dietary sources of energy, providing approximately 9 kcal/g when metabolized compared with 4 kcal/g for carbohydrates and proteins, and account for about 36 percent of domestic caloric intake per capita.19 Dietary lipids also can provide essential molecular structures that are synthesized by the body into compounds required for selective functioning of cell membranes and regulation of life processes. 

Vitamins are minor components of foods that play an essential role in human nutrition. Many vitamins are unstable under certain conditions of processing and storage (Table 9-1), and their levels in processed foods, therefore, may be considerably reduced. Synthetic vitamins are used extensively to compensate for these losses and to restore vitamin levels in foods. The vitamins are usually divided into two main groups, the water-soluble and the fat-soluble vitamins. The occurrence of the vitamins in the various food groups is related to their water-or fat-solubility. The relative importance of certain types of foods in supplying some of the important vitamins is shown in Table 9-2. Some vitamins function as part of a coenzyme, without which the enzyme would be ineffective as a biocatalyst. Frequently, such coenzymes are phosphorylated forms of vitamins and play a role in the metabolism of fats, proteins, and carbohydrates. Some vitamins occur in foods as provitamins—compounds that are not vitamins but can be changed by the body into vitamins. Vitamers are members of the same vitamin family. 

Guillon, E M. M-J. Champ. Carbohydrate fractions of legumes Uses in human nutrition and potential for health. Brit. J. Nutr. 2002, 88, S293-S306. 

It is interesting therefore to review what evidence there is of deranged carbohydrate metabolism under conditions of AA and DHA depletion. The reviewer has not been able to find any reference to deranged carbohydrate in human scurvy. Crandon s glucose tolerance was unaffected by scurvy (Crandon et al., 1940). There is some indecisive literature on the alleged effect of diets low in ascorbic acid on the human glucose tolerance test, but Owens et al. (1941) were unable to show that clinical diabetes was affected in any way by the state of ascorbic acid nutrition. 

S. is very important in human nutrition, supplying most of the dietary carbohydrate requirement (humans require about SOO g carbohydrate per day). Potatoes, cereals and bananas are particularly rich in S. Metabolism of 1 g S. supplies 16.75 kJ (4 kcal). S. is prepared commercially from plant sources, in particular potatoes, wheat rice and maize, and it has many uses in the food industry and in technology. 

Fat is needed in human nutrition for growth and replacement of tissues, for certain lipid secretions, and as a source of energy. The optimal level of fat in the diet is not known, and since fat may be formed from carbohydrate or protein, no definite requirement can be formulated. Fat increases the palatability of the diet and also reduces the bulk, since the energy value of fat is more than twice that of an equivalent amount of protein or carbohydrate. Dietary fat also acts as a carrier for the fat-soluble vitamins. 

Starch is widely distributed in various plant organs as a storage carbohydrate. As an ingredient of many foods, it is also the most important carbohydrate source in human nutrition. In addition, starch and its derivatives are important industrially, for example, in the paper and textile industries. 

In human nutrition, nutrients are often inaccurately classified in a way that reflects the amount that the body requires. These nutrient classes can be categorised as either macronutrients (required in relatively large amounts) or micronutrients (required in smaller amounts). The macronutrients include proteins, fats, carbohydrates and water the micronutrients are minerals and vitamins. A third class of dietary material, known as fibre (such as non-digestible polysaccharide cellulose), is also necessary, for both mechanical and biochemical reasons. Other micronutrients include antioxidants and various phytochemicals, which are said to influence or protect some body systems. Their necessity is not well estabhshed. 

The principal cereal grain crops of the world, in descending order of production, are wheat, corn, rice, barley, sorghum, oats, rye, and millet. The cereals supply most of the carbohydrates in human diets throughout the world and the proteins, oils, minerals, and vitamins contained in cereals are also of considerable nutritional importance. 

Plants, in contrast to animals, have the ability to convert carbon dioxide from the atmosphere and inorganic components of the earth direcdy into high energy carbohydrates (qv), fats, and proteins (qv). These plant materials are absolutely essential to human nutrition as well as to the nutrition of other animal species. Thus consumption of plant matter, either directly or through a food chain, is essential to animal life and humans are totally dependent on agricultural endeavors, ie, the culture and harvesting of plant matter. 

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