A calorie (cal) is the amount of heat energy required to raise the temperature of 1g of water 1’C from 14′ to 15’C.
The standard unit of measure is kilocalories or kilojoules per 100 g of food or beverage consumed.
One pound of fat = 3500 calories.
Caloric values of foodstuffs include 4.1 kcal/g of carbohydrate, 9.3 kcal per gram of fat, and 5.3 kcal/g of protein, and similar values are available for the body for carbohydrates and fat, but protein metabolism leads to the end products of urea, nitrogenous compounds, CO2 and water, with a value 4.1 kcal/g.
Estimated energy requirements is 30 kcal per kilogram of body weight per day in mobile persons with limited physical activity, and 25 kcal per kilogram per day in bedridden patients, and hospitalized and critically ill patients recommendations are 75% of calculated injury requirements at 18 to 20 kcal per kilogram per day.
Over the past 30 years the total calorie intake has averaged an increase 150-300 calories per day.
Overfeeding studies reveal that calorie expenditure increases progressively, because energy costs of maintaining the newly created tissues.
When a calorie of food energy is consumed, one of three effects occur within the body: a portion of that calorie may be stored as body fat, triglycerides, or glycogen, transferred to cells and converted to chemical energy in the form of adenosine triphosphate (ATP – a coenzyme) or related compounds, or dissipated as heat.
With weight loss the body size diminishes, and changes in hormones, the autonomic nervous system, and muscle efficiency all serve to conserve energy: requiring that additional weight loss can be achieved by more severe dieting or more arduous physical activity.
Muscle tissue is three times more efficient at burning calories than fat.
Lean muscle uses more calories than fat.
Indirect calorimetry is used to determine the metabolic rate.
Energy production is calculated by measuring the products of energy producing biologic oxidation:CO2,H2O and products of protein catabolism.
Measurement of O2 consumption determines the metabolic rate by indirect calorimetry.
Respiratory quotient (RQ) is the ratio in the steady state volume of CO2 produced to the volume of O2 consumed per unit of time.
R, is the respiratory exchange ratio, the ratio of CO2 to O2 at any given time.
R is affected by factors other than metabolism.
The RQ for carbohydrate is 1.0 and for fat is 0.7-the H and O are present in in carbohydrate in the same proportions as in water, whereas in fats extra O2 is necessary for the formation of H2O.