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The implications of all this are that someone who is unfit is less efficient at using fat in the fuel mix for exercise than someone who is fit, and that this difference increases with the intensity and duration of the exercise. Fat utilisation in an unfit person would therefore only be optimal at an exercise intensity much lower than that required for a fit person—in both absolute and relative terms. This then, gives a totally different outlook to the approach often promoted by the fitness industry based on the ‘no pain, no gain’ philosophy.
There have also been suggestions that the majority of the energy deficit resulting from physical activity is supplied by fat after the activity, or in ‘excess post-exercise oxygen consumption’ (EPOC), and hence the amount of fat oxidised during the exercise is only part of the story. If this were the case, the total energy use during exercise is again likely to be the biggest factor influencing fat use. However, if we look at this suggestion closely, we see that it is likely to be true first only if the exercise is sustained long enough to significantly deplete glycogen stores, thus diminishing their function as the primary energy source and second, if no carbohydrate is eaten post-exercise, in which case this would take priority as the energy source and fat would once again be ’saved’, and deposited into fat stores. This proposal also doesn’t explain the increased high rate of re-esterification of fat that occurs in EPOC, particularly in women, probably in defence of their reproductively important energy sources. This is opposed to the approach of re-loading carbohydrate stores for energy after exercise in athletes that is commonly agreed to by exercise physiologists. It does suggest that the issue of type of food intake relating to exercise is more complicated than may first seem.
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People working in the obesity area use the term weight control, and the measure of weight as their surrogate measurement of body fatness. Yet degree of fatness only partially contributes to body weight. Muscle tissue is almost two-and-a half times as dense as fat tissue and therefore a muscular person is likely to weigh more than a fat person of the same overall body size. Hence a fit, exercising person with a high muscle density is likely to weigh more, but have a much lower fat level than an unfit, fat person.
Weight is the combination of a range of things; bones, organs, muscle, even the length you grow your hair; whereas fat, if measured properly, is just fat. The difficulty, of course, is in accurate measurement. There are no simple, accurate measurements for body fat. So far, there are only reasonable estimates. Still, these existing measurements are likely to give a better estimate of fatness level than the more general measure of body weight. A change in body weight, however, usually reflects changes in fat mass and lean mass (particularly in women), and hence the terms weight and weight control, while not technically correct, are still used as a form of convenience.
We tried to use the terms fat and overfatness where this is a more accurate representation of the situation, except where referring to weight as such, or where this is used to describe other work more specifically directed at weight. Despite their awkwardness, the terms overfatness and fat control are used where possible in an effort to get those working in this area to use the appropriate terminology. However, most studies, especially in larger populations, have to rely on some form of weight measurement as a surrogate for fatness.
Myth-Information. Rapid weight less, as advertised in many ‘diet-style’ programs, has been found to be not only potentially dangerous, but to increase the speed with which weight is put back on. Weight loss greater than 1.5kg per week dramatically increases the risk of disease.
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