FITNESS AND FATNESS

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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