COMPONENTS OF ENERGY EXPENDITURE

When dealing with the area of managing body fat levels we must have a basic understanding of how energy is balanced in the body. We consume on average anywhere from 1500kcal-2500kcal per day. This adds up to an energy intake of about 555 000-1 million kcal (2.33-4.17 kj) per year. But what about expenditure? How does the body balance energy intake with expenditure? Why can some individuals seemingly consume relatively greater quantities of food than others, and at the same time end up with lower stores of body fat? Dr Klaas Westerterp and his group from the University of Limberg in the Netherlands, have estimated that over the course of a lifetime, there is an actual discrepancy between energy intake and energy expenditure of only around 1 per cent, making the system an extremely well balanced one.2 What this implies, of course, is that body weight is not just equal to the amount of energy intake minus energy expenditure, but that energy intake + expenditure must change, as a function of a number of factors, to help balance the system. To understand this, we need to understand the components of energy expenditure. There are three main components of energy expenditure.

1. Resting metabolic rate (RMR) or basal metabolic rate (BMR), which equals sleeping metabolic rate (SMR) and arousal.

2. The thermogenic effect of food.

3. Exercise, or daily physical activity and spontaneous physical activity (SPA).

The vast majority (i.e. around 70 per cent) of daily energy expenditure (EE) in the average person is accounted for by RMR. Thermogenesis contributes about 15 per cent and daily physical activity is the most variable being around 10-25 per cent in sedentary individuals.

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