Dietary carbohydrate, sources

The fat content of the US diet has increased very substantially over the past few decades. Currently more than 40% of dietary calories are consumed in the form of fat. This can easily lead to weight gain. The energy required for conversion of dietary fat to fat in adipose tissue involves the loss of only 3% of the calories in the dietary fat. In contrast, the energy requirement for conversion of dietary carbohydrate to fat in adipose tissue involves the loss of 23% of the calories in the dietary carbohydrate. Clearly, dietary fat is a great source of body fat. 

Lipids serve as an important source of dietary energy for all fish and to a greater extent for cold-water and marine fish, who have a limited ability to use dietary carbohydrates for energy. Increasing the lipid content of some diets has also been effective in decreasing protein requirements in some applications (11). 

Lipogenesis, the synthesis of fatty acids and their esterification to glycerol to form triacylglycerols, occurs mainly in the liver in humans, with dietary carbohydrate as the major source of carbon. 

In other studies, the effects of high-fibre diets on blood glucose levels were generally felt to be rather small (Simpson et al., 1981), and it was noted that postprandial blood glucose levels are influenced only when fibre content is fivefold higher than that of the normal British diet, whereby the effects of the dietary fibre source on carbohydrate metabolism seem to depend on the composition of the source. 

The effects of carbohydrate and fat on the efficiency with which dietary iron is converted into hemoglobin have been studied. Hiller and Landes (1976) used starch, sucrose or glucose as the carbohydrate source and ferrous sulfate as the iron source. The respective efficiencies of converting dietary iron into hemoglobin were 72, 65, and 46 percent. 

Amine and Hegsted (1971) obtained similar carbohydrate effects studying iron absorption. Glucose is the most commonly used source of dietary carbohydrate in semipurified diets. Pennell et al. (1976) reported that beta-lactose in place of sucrose reduced the relative biological value of iron as sodium iron pyrophosphate when fed to rats. However, alpha-lactose or glucose in place of the sucrose did not affect the bioavailability of this iron source. Similarly, the source of fat can affect the bioavailability of dietary iron but, the level of dietary fat has no effect (Mahoney et al., 1980). 

Carbohydrates are found in a wide variety of naturally occurring substances and serve as principal energy sources for the body. Dietary carbohydrates include complex carbohydrates, such as starch in potatoes, and simple carbohydrates, such as sucrose. 

Immediately after a meal, dietary carbohydrates serve as the major source of blood glucose (Fig. 31.20). As blood glucose levels return to the fasting range... 

Fatty acids are synthesized whenever an excess of calories is ingested. The major source of carbon for the synthesis of fatty acids is dietary carbohydrate. An excess of dietary protein also can result in an increase in fatty acid synthesis. In this case, the carbon source is amino acids that can be converted to acetyl CoA or tricarboxylic... 

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. 

Beaton, G. H., Milner, J., McGuire, V., Feather, T. E., and Little, J. A., 1983, Sources of variance in 24-hour dietary recall data Implications for nutrition study design and interpretation. Carbohydrate sources, vitamins and minerals. Am. J. Clin. Nutr. 37 986. 

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