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Thermic Effect of For Losing Weight While Pregnancy Food

The TEF, also known as dietary-induced thermogenesis, is the amount of energy expended for digestion, absorption, metabolism, and storage of food in the body. This amount is above REE and comprises about 10 percent of TEE. The TEF is affected by various characteristics of the food consumed, though the total energy (calorie) content of the food has the greatest impact on TEF. The macronutrient content of the food (carbohydrate, protein, fat, and alcohol) also impacts the TEF. Fat has the lowest TEF using only 2 to 3 percent of the calories consumed from fat. Carbohydrate has a TEF of 5 to 10 percent of carbohydrate calories consumed, and protein has the highest TEF, requiring 20 to 30 percent of calories ingested from protein for its metabolism that relates to protein’s impact of satiety after a meal. This is one of the reasons why diets high in protein are reported to have greater satiety and may help with weight management goals. While alcohol has a TEF of about 10 to 30 percent, it does not seem to have the same effect on satiety as protein (Westerterp 2004).

Measuring Thermic Effect of Food. TEF can be measured in a research laboratory. This is rarely done because it is usually not feasible nor is it very practical. Instead, TEF can be calculated by multiplying 10 percent to the total caloric intake of the diet. For example, an individual consuming 2,400 calories would have a TEF of 240 calories. However, because the contribution of TEF is relatively small compared to that of RMR, it usually is not factored into TEE estimates. TEF lasts only 1 to 2 hours after consuming a mixed meal and so the overall impact is fairly minimal.

Physical Activity

Physical activity, or PA, is the third component of TEE. This includes the amount of energy expended on ADLs, or the basic tasks of everyday life. Cooking, cleaning, getting dressed, energy expended while working, at school, and other daily tasks are all considered ADLs. Physical activity expenditure also includes the energy used for structured exercise; for athletes, this amount can be quite considerable.

Physical activity energy expenditure is the most variable component of TEE. Physical activity is estimated to comprise about 20 to 30 percent of TEE, though this value can vary widely according to the lifestyle habits and exercise patterns of the individual. Individuals have the most control over this component of TEE; minimal changes can be made to REE, and TEF is relatively static. Yet, the amount of energy one expends on a daily basis engaging in activity can have a profound effect on total energy expended. If an individual has a sedentary job where one sits most of the day, and does not engage in structured exercise or in other daily activities such as cleaning or gardening, the PA energy expenditure will be relatively minor. On the other hand, individuals working active jobs, such as manual labor positions, and also exercise on a daily basis will have a significantly greater contribution of PA energy expenditure toward TEE.

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Even within an individual, daily activity can vary greatly. An athlete who works a sedentary job and has a “rest” day from training may only have a small PA expenditure. A 120 lb female runner, for example, who works a desk job and does not exercise on a given day, may only need 1,750 calories to meet her energy needs. This represents a 20 percent increase in calories over her RMR. On a hard training day where she has a long run and then engages in house cleaning the rest of the day may need upward of 2,600 calories. This is an almost 90 percent increase in calories over her RMR! Obviously daily activity levels can significantly impact TEE.

Measuring Physical Activity. Ensuring that PA energy expenditure is accurately assessed is essential for providing appropriate energy recommendations for athletes. Looking at the female runner in the aforementioned scenario, failing to adjust her calorie intake to meet her daily needs could have adverse effects. This runner could end up overeating if she maintained a daily caloric intake comparable to what her needs are on a high activity day; alternatively, she could end up grossly undereating if she only consumed the amount of calories she needed for her low-activity days even on high-volume training days. This inflexible calorie consumption could have deleterious effects on her health and performance. Therefore, athletes must adjust their caloric intake according to daily fluctuations in PA, requiring the ability to estimate daily PA expenditure.

Indirect measures of energy expenditure. The best way to assess physical activity energy expenditure is to use indirect measures including indirect calorimetry via open-circuit spirometer and metabolic chamber. This process uses feedback from the individual including O2 inhaled and CO2 expired to measure energy expended during exercise. This can be done in a research or exercise physiology and biomechanics laboratory, or a portable metabolic cart can be used in the athlete’s typical environment. In either scenario, when machines are calibrated and used appropriately, this can be a relatively accurate measurement of PA energy expenditure.

Metabolic equivalents of a tasks and the Compendium of Physical Activity. Physical activity questionnaires can be utilized as a way to assess daily physical activity levels. While there exist multiple physical activity questionnaires, many rely upon the Compendium of Physical Activities to provide an assessment of energy expenditure based upon the details of physical activity. Initially developed in 1989 and published in 1993, the Compendium of Physical Activities provides a coding scheme for various physical activities. These activities are then linked to the appropriate intensity level, which is measured by a metabolic equivalent of a task, or MET (Ainsworth et al. 2000). A MET is a ratio of the metabolic rate during a specific activity to a reference metabolic rate of 1.0 kilocalorie per kilogram per hour (1.0 kcal/kg/hr). METs are based on the measurement of oxygen consumption (mL per kilogram per minute, or, mL/kg/ min), with the assumption that 1 MET equals the oxygen cost of sitting quietly of about 3.5 mL/kg/min.

The updated 2011 Compendium provides an extensive list of coded activities in different settings linked with their respective MET. This list is the most globally recognized set of values for METs and includes over 800 coded activities ranging from truck driving to ballroom dancing. The MET values range from 0.9 METs for sleeping to 23 METs for running 14.0 mph (Ainsworth et al. 2011). Based on the physical activity type and intensity per unit of time, METs can provide an estimate of energy expenditure. The equation factors in body weight, since an individual’s weight affects caloric expenditure. The equation is as follows: MET x weight (kg) x duration (hours). So, remembering the 120 lb female runner identified earlier, let’s say she ran 6.5 mph for 1.5 hours. The Compendium value for running at that speed in 12.8 METs. Using the equation, her energy expenditure while running would be: 12.8 METs x 54.5 kg x 1.5 hours = 1,047 kcal.

It is important to realize that MET values included in the Compendium, and most forms of physical activity energy expenditure measurements, include REE. That is, the 1,047 calories expended by the distance runner during her run is not just the energy needed for the activity of running, but includes the energy needed for the ongoing basal metabolic functions during this period of time. Thus, when calculating TEE by using estimates of energy expenditure for physical activity (such as METs), REE does not need to be added.

Using METs and the Compendium of Physical Activity has limitations as with any assessments using preestablished values to determine a measurement. One weakness with using METs is that the measurement assumes that all individuals expend 3.5 mL O2/kg/min at rest, and this establishes the basis for other MET values. In actuality, this value may vary among individuals, such as someone who may only need 3.1 mL OJ kg/min at rest, or conversely, someone may require 3.9 O2/kg/min. This assumption that all individuals consume 3.5 mL O2/kg/min could result in over- or underestimating energy expenditure, respectively. So, while MET values may not provide a precise value for energy expenditure, it can at least provide relative information. Looking at the example of the female distance runner, using METs it is estimated that she expends 1,047 calories during her 90-minute run. This value may not have high accuracy, but calculating METs for different durations and intensity (pace) she can get a gauge of her relative energy expenditure. Even considering its limitations, METs can provide a practical assessment tool for energy expenditure for various physical activities.

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