Carbohydrates energy content

Figure 10. The relationship between the initial glycogen content in vastus lateralis muscle and work time in six subjects who cycled to exhaustion at 75% VO2 max. Each subject cycled to exhaustion on three occasions. The first experiment was preceded by a mixed diet (a), the second by a carbohydrate-poor diet (o), and the third by a carbohydrate-rich diet ( ). The energy contents of the diets were identical. In all experiments depletion of the muscle glycogen store coincided with exhaustion and muscle fatigue. From Bergstrom et al. (1967) with permission from the publisher.

Hopkins was careful to apply the governing rule of nutrition to his experiments all the dietaries were more than adequate with respect to their energy content. With rare exceptions the rats used in his studies consumed sufficient food, fats and carbohydrates in particular, to supply them with the calories deemed necessary for growth. The quantities of protein and of mineral salts were also adequate. With all this in mind, attention can now be focused on the specific diets, experimental procedures and results. 

Carbohydrate accounts for about 40% of the energy content of a normal meal. In the UK, the daily intake is typically 60 g starch, 120 g sucrose, 30 g lactose, 10 g of glucose... 

Relevance to potatoes Potatoes have thin cell walls so are not rich in NSPs. They are a valuable source of carbohydrate energy, but would not on their own provide enough dietary fiber to meet daily requirements. Increasing RS levels partially compensates for the low dietary fiber content of potatoes. 

J to their molecular components. Then one of two things happens either your body burns these molecular components for their energy content through a process known as cellular respiration, or these components are used as the building blocks for your body s own versions of carbohydrates, lipids, proteins, and nucleic acids. The sum total of all these biochemical activities is what we call metabolism. Two forms of metabolism are catabolism and anabolism, and Figure 13.41 shows the major catabolic and anabolic pathways of living organisms. 

Although different sugars have different sweetness factors relative to sucrose they are all identical in energy content, on a dry basis. Thus to achieve a high energy content without cloying sweetness, sugars or carbohydrates of low sweetness must be used. This is illustrated in Table 13.2. 

Fats and oils serve as energy reserves for the organism. Because they are in a lower oxidation state than carbohydrates, they provide more energy per gram when they are metabolized (see the Focus On box Energy Content of Fuels in Chapter 5). 

The first law of thermodynamics allows us to rate foods in terms of their energy contents. These are really AH of combustion values. Thus, carbohydrates, fats, proteins, and ethanol yield approximately 4, 9, 4, and 7 kcal/g, respectively when combusted. A normally active person requires between 2000 and 2500 kcal/day in foodstuffs to function normally. Persons doing heavy work may require as much as 5000 kcal/day or more. 

Almost every aspect of human life involves carbohydrates in one form or another. Like other animals, we use the energy content of carbohydrates in our food to produce and store energy in our cells. Clothing is made from cotton and linen, two forms of cellulose. Other fabrics are made by manipulating cellulose to convert it to the semisynthetic fibers rayon and cellulose acetate. In the form of wood, we use cellulose to construct our houses and as a fuel to heat them. Even this page is made from cellulose fibers. 

Tl ie energy content of food carboliydrate and food protein is J7 kj/g, whereas that of food fat is 38 kj/g. The energy content of ethanol is 3 kJ/g. Though fairly accurate, these values are only generalizations. For example, consider the energies of different carbohydrates 17,2 kJ/g of starch, 16.6 kJ/g of sucrose, 15,9 kJ/g of glucose. 

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