![]() Even at stable body weight, however, the percentage of body fat frequently increases with age unless regular physical activity is maintained. When intake equals expenditure, equilibrium results and body fat is maintained, regardless of whether the body weight is at, above, or below normal. When energy expenditure exceeds energy intake, energy balance is negative and leads to weight loss. Increased fat storage is appropriate during pregnancy and lactation, during some periods of growth and development, and during recovery from trauma or malnutrition, but it may not be desirable under other conditions. Less energy expenditure than energy intake results in a positive energy balance and storage of energy primarily as body fat. One kilocalorie (equivalent to 4.184 kJ) is the amount of heat required to raise the temperature of 1 kg of water 1☌ (e.g., from 15 to 16☌) at standard atmospheric pressure (760 mm Hg).Įnergy balance refers to the relationship of energy intake to energy expenditure and energy storage. In biologic systems it is usually measured in kilocalories (kcal) or kilojoules (kJ). When more energy is consumed than is needed for metabolism and physical activity, the excess is stored, primarily as adipose tissue.Įnergy is the capacity to do work. Food energy is used to meet the body's needs, including protein synthesis maintenance of body temperature, cardiac output, respiration, and muscle function and storage and metabolism of food sources of energy. In some underweight subjects, however, malabsorption of nutrients is an important factor. Studies of normal and overweight subjects have not shown any significant differences in the proportion of food energy absorbed. ![]() Under normal circumstances, more than 95% of this food energy is digested and absorbed from the gastrointestinal tract to provide the body's energy needs. ![]() Carbohydrates, protein, fats, and alcohol-the dietary macrocomponents-are the sources of energy in the diet. ![]()
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