The total energy expenditure is defined as the energy expended by a living organism over a fixed period of time. It is often encountered in the context of weight loss, expressed as the energy in calories expended per day. The biggest contributor is the basal metabolic rate, which is the energy expended per day to maintain body metabolism. Understanding how to calculate the total energy expenditure is useful when using calorie counting as a method of weight loss.
Basal Metabolic Rate
Basal metabolic rate is the energy required per day to maintain bodily processes in the absence of having to do work or actively regulate body temperature. It is the largest expenditure in practice, accounting for around 70 percent of the body's total energy expenditure, though this depends greatly on the level of activity. Energy is required to maintain muscle mass, even when at rest, so weight training that does not directly consume much energy can increase the basal metabolism, and so can aid in fat loss. The basal metabolic rate in calories needed per day can be calculated from weight, height, and age using online tools, or as follows: multiply your weight in kilograms by 10 and add 6.25 times your height in centimeters. Then subtract 5 times your age in years and then subtract 166 if you are female or add 5 if you are male. This is according to the newer Mifflin-St.-Jeor formula. Older formulas, such as the Harris-Benedict formula, give slightly different numbers.
Total Energy Expenditure
The total energy expenditure is calculated from the basal metabolic rate by multiplication by an activity factor to account for the additional energy spent due to physical activity. The activity factor is always greater than one, as nobody can be in a permanent resting state. To obtain the total energy expenditure, multiply your basal metabolic rate by the appropriate factor reflecting your level of exercise: sedentary is 1.2, lightly active is 1.375, moderately active is 1.55 and very active is 1.725. For extremely active use 1.9. "Lightly active" corresponds to someone who occasionally exercises, "moderately active" means regular exercise, "very active" means an hour of intense exercise every day, and "extremely active" means multiple hours of intense exercise per day, which would include professional athletes.
Energy Balance Principle
The value of knowing your total energy expenditure is that it can help you lose weight based on the principle of energy balance. Excess body fat is basically stored energy that can be used by the body as needed. In order to lose weight it is necessary to achieve an energy deficit, where the total energy expenditure of the body exceeds energy taken in the form of food and beverages. The deficit has to be made up somehow, so body fat is burned, leading to weight loss.
A 2012 controlled study by Ebbeling et al. in the Journal of the American Medical Association demonstrated that the caloric value of diets alone may not be the sole determinate of weight loss, as dietary composition can affect the basal metabolism differently, even if the consumed calories -- the most-often-used measure of energy -- are the same. Diets low in fat may cause a lower basal metabolic rate, smaller calorie deficit and less weight loss than diets that contain a higher percentage of fat. Extreme calorie restriction can result in the body going into "starvation mode," in which the basal metabolic rate is substantially reduced, also curtailing weight loss compared to what would otherwise be expected.
- American Journal of Clinical Nutrition: A New Predictive Equation for Resting Energy Expenditure in Healthy Individuals
- Frontiers in Nutrition: Assessment of Physical Activity and Energy Expenditure: An Overview of Objective Measures
- Journal of the American Medical Association: Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance
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