Basic Concepts of Energy Requirements
Energy Balance – is described by the following equation. Intake = Oxidation + Storage + Excretion
- Oxidation – includes basal metabolism (varies little), thermogenesis, and activity (highly variable)
- basal rate has to do with temperature regulation as well as Post Parengeal thermogenesis (the extra O2 consumption that occurs after a meal). Activity can be very little (e.g. studying) or a great deal (e.g. running).
- Storage – usually negligible, but can increase during pregnancy. A normal human adult carries around a three month supply of extra energy. Infants have only a 3 week reserve (have higher metabolism than adults; 100 kcal/kg/day, compared with 30 kcal/kg/day in adults). Reserves consist of lots of triglycerides, some protein, and little glycogen. Excess calories are mainly stored as fat.
- Excretion – very little energy is lost in stool or urine, can be significant during lactation
- Malabsorption – lose calories in the stool
- Diabetes mellitus (DM) – lose calories in the urine
- US adult males consume an average of 3040 kcal/day (range1185-5840), US females 1687 (range 670-3009)
caloric intake vs. weight change graph is linear
weight change is used to track energy balance, but H2O changes make this method error prone
INTAKE = UTILIZATION no change in weight. If In > Out Þ weight gain, if In < Out Þ weight loss
slope = "Cost of Energy Change"
History of Intake or direct measurement of intake can be used (easier to do when on a liquid diet)
Measurement of Metabolic Activity: either Basal (via temp) or Total (via O2 consumption)
There is a direct relationship between activity and oxygen consumption
Energy Value of Weight Change
a conversion factor which relates changes of body weight to stored energy.
The average value of a kg of weight gained or lost is 6000 kcal
- (Weight Change) = (Energy Intake – Utilization) / (Cost of Energy Change)
- Units: (kg) = (kcal) / (kcal/kg)
- variations from the average: primarily due to amount of body water gained or lost. In later phases due to fat.
Treatments of Starvation and Obesity
liquid formula of high caloric density and low osmolality is used to establish rapid recovery from undernutrition. All essential nutrients must also be provided. Vegetable oil is the major source of calories (60% fat, 30% starch, and 10% protein). Rapid recovery shortens hospital stays and minimizes rates of complications. Treatment of malnutrition secondary to other diseases frequently involves special techniques (e.g. parenteral nutrition).
Obesity – increasing utilization by exercise and decreasing intake will take off those excess pounds.
- (Weight Change) = ( ß Energy Intake – Ý Utilization) / (Cost of Energy Change)