Info

8.7 W + 829

0.0364 W + 3.47

>60

10.5 W + 596

0.0439 W + 2.49

W, body weight expressed in kilograms; MJ, megajoules. (Data from WHO (1986) Energy and Protein Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. Technical Report Series 724. Geneva: World Health Organization.)

W, body weight expressed in kilograms; MJ, megajoules. (Data from WHO (1986) Energy and Protein Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation. Technical Report Series 724. Geneva: World Health Organization.)

Thermic Effect of Food or Postprandial Thermogenesis

The energy expenditure increases significantly after a meal. The thermic effect of food is mainly due to the energy cost of nutrient absorption and storage. The total thermic effect of food over 24 h represents -10% of the total energy expenditure in sedentary subjects. The thermic effect of nutrients mainly depends on the energy costs of processing and/or storing the nutrient. Expressed in per cent of the energy content of the nutrient, values of 8%, 2%, 20-30%, and 22% have been reported for glucose, fat, protein, and ethanol, respectively.

Glucose-induced thermogenesis mainly results from the cost of glycogen synthesis and substrate cycling. Glucose storage as glycogen requires 2 mol ATP/mol. In comparison with the 38 mol ATP produced on complete oxidation of glucose, the energy cost of glucose storage as glycogen corresponds to

Table 3 Determinants of resting (basal) metabolic rate

• Body composition (lean vs. obese)

• Physiological status (growth, pregnancy, and lactation)

• Hormonal status (e.g., Follicular ve luteal phase)

- Temperature (body internal and environment)

- Pharmacological agents (e.g., nicotine and caffeine)

5% (or 2/38) of the energy content of glucose stored. Cycling of glucose to glucose-6-phosphate and back to glucose, to fructose-1,6-diphosphate and back to glucose-6-phosphate, or to lactate and back to glucose, is occurring at variable rates and is an energy-requiring process that may increase the thermic effect of carbohydrates.

The thermic effect of dietary fat is very small; an increase of 2% of its energy content has been described during infusion of an emulsion of triglyceride. This slight increase in energy expenditure is explained by the ATP consumption in the process of free fatty acid reesterification to triglyceride. As a consequence, the dietary energy of fat is used very efficiently.

The thermic effect of proteins is the highest of all nutrients (20-30% of the energy content of proteins). Ingested proteins are degraded in the gut into amino acids. After absorption, amino acids are deaminated, their amino group transferred to urea, and their carbon skeleton converted to glucose. These biochemical processes require the consumption of energy amounting to ^25% of the energy content of amino acids. The second pathway of amino acid metabolism is protein synthesis. The energy expended for the synthesis of the peptide bonds also represents ^25% of the energy content of amino acids. Therefore, irrespective of their metabolic pathway, the thermogenesis induced after absorption of amino acids represents ^25% of their energy content.

Energy Expenditure Due to Physical Activity

The energy spent on physical activity depends on the type and intensity of the physical activity and on the time spent in different activities. Physical activity is often considered to be synonymous with 'muscular work', which has a strict definition in physics (force x distance) when external work is performed in the environment. During muscular work (muscle contraction), the muscle produces 3-4 times more heat than mechanical energy, so that useful work costs more than muscle work. There is a wide variation in the energy cost of any activity both within and between individuals. The latter variation is due to differences in body size and in the speed and dexterity with which an activity is performed. In order to adjust for differences in body size, the energy cost of physical activities are expressed as multiples of BMR. These generally range from 1 to 5 for most activities, but can reach values between 10 and 14 during intense exercise. In terms of daily energy expenditure, physical activity accounts for 15-40% of total energy expenditure but it can represent up to 70% of daily energy expenditure in an individual involved in heavy manual work or

Table 4 Exogenous and endogenous factors influencing the three components of energy expenditure

Components

Endogenous

Exogenous

• Basal

Fat-free mass

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