RER (respiratory exchange ratio) measures, or the measure of fat and glucose utilisation, need to be looked at for intensity and duration of exercise both for fit and unfit (possibly fat) people, to gain a better appreciation of the appropriate form of exercise for those most likely to be carrying excess fat.

More vigorous exercise obviously burns more total energy in a given time period, but the graph shows that, at least in the unfit, under normal conditions (i.e. no excessively restricted energy intake), higher intensity exercise is likely to be less effective for fat loss. In other words, for an unfit person, the total amount of exercise at this intensity—even if it could be carried out by an unfit person—would not result in substantial fat loss. For a fit person, however, high intensity exercise is associated with fat burning.

Similar difference between the fit and the unfit can be seen, suggesting that the longer the effort—at least at moderate intensity—the greater the proportion of fat used in the energy cycle. In the unfit though, some of the research quoted above suggests that this may be true only up to a point, beyond which there is likely to be a decrease in fat utilisation and an increased reliance on glycogen. As fatigue sets in glycolysis plays a more important part, and glucose is thus likely to become more important as an energy source for the unfit.

These suggestions have been shown in practice in research by Dr David Kelly from the University of Pittsburgh.10 Kelly exercised obese people over a week for either 50 minutes at 70 per cent of their maximum capacity, or for 70 minutes at 50 per cent of their maximum. Both treatments resulted in exactly the same calorie expenditure. But the RER and total fat oxidation were higher for the longer, less intensely exercised group. Their total fat utilisation was estimated to be 24.5 grams for the 70 minutes, compared to 131 grams for the more intensely exercised group. Because fat utilisation is known to decrease in the unfit with duration of exercise, this suggests that for unfit people, fat utilisation would be even greater in the less intense group if the same time period (i.e. 50 minutes) was used for exercise.

All this suggests a change in thinking about the right parameters of exercise for fat loss in unfit (which include most fat) people. The FITT (frequency, intensity, time and type) mnemonic may be appropriate for improvements in fitness, but this needs to be modified for changes in fatness—at least in fat, unfit people.

Even this model has reservations when it comes to prescribing exercise for specific population sub-groups (women, older people, children etc.). Interestingly though, the new FATT factors also agree with the physical activity requirements for wider health gains. Several recent long term studies have shown that high intensity exercise is not necessary for health, or metabolic improvements, such as decreased risk of heart disease. Regular, low intensity, long duration activities can be sufficient to provide these improvements. Recently, it has also been shown that in obese people, short (10-minute) bursts of exercise, four times daily, are more effective in fat loss (and even in fitness gained) than continuous (40-minute) bouts. This is primarily because it is easier for obese people to comply with the demands of shorter bouts.

Myth-information. ‘Digital tummy trimmers’ are designed to force the abdominal muscles to contract against a tight belt. At best, this may increase some isometric muscle strength in the abdominals. It will have no effect on subcutaneous fat.

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The usual definition of overfatness or overweight is up to 20 per cent over a recognised ideal body weight, or a body mass index (BMI) (or height-weight measure) of 25-29.9- BMI is a measure using weight divided by height squared (kg/m2); the normally recognised ‘ideal’ is a BMI of 20-25. Obesity is regarded here as a BMI of 30-39.9; and morbid obesity as BMI over 40.

Summary of main points.

• Almost 1 in 2 people in western countries are now defined as overweight or obese.

• People in some Western countries have been increasing body weight at the average rate of 1g/day over the last decade.

• ‘Overfatness’ is a more appropriate term than ‘overweight’.

• The fitness and nutrition booms have had little impact on levels of fatness throughout the world.

• The environment determines prevalence, and genes determine the presence of obesity.

• The traditional paradigm of ‘weight=energy in (food)— energy out (exercise) is no longer adequate for understanding obesity.

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