The three days of fatty foods were fun for athletes who normally followed the strict dictates of healthful, high-carbohydrate eating, and early studies carried out in Sweden indicated that the overall plan could hike glycogen to extraordinary levels and promote superior endurance performances.

Unfortunately, subsequent research showed that the 'depletion' phase of the procedure - the knock-out workout and three days of fat - wasn't really necessary to super-concentrate glycogen. In fact, its main effect seemed to be the production of tired, somewhat cranky athletes. As a result, endurance performers went back to the old humdrum of consistent carbohydrate intake.

However, research carried out last year at the University of Indiana revived the possibility that fat might be fit food for endurance kings. The Indiana investigations suggested that athletes who sup on fat for long periods of time - over a week or so - might convert their muscle cells into special, fat-burning fibres with an increased capacity to conserve glycogen. Capping the fat consumption with a couple of days of high-carbohydrate eating would then lead to extraordinarily high levels of muscle glycogen, because muscle cells, accustomed to using fat to satisfy their energy needs, would simply stockpile the incoming carbohydrate in record amounts. Initial studies with laboratory rats indicated that the prolonged fat plus short-term carbohydrate pattern could bolster endurance in certain situations. We reported on this research in the June issue of PP.

However, the 'fat-first, then-carbo' strategy hadn't been tried out with human subjects - until now. Recently, scientists at the University of Cape Town asked endurance-trained cyclists to consume either their normal diets (less than 30 per cent of total calories from fat) or special high-fat diets (more than 65 per cent of calories from fat) for a period of 10 days. Following the 10 days of normal eating or high-fat dining, the athletes capped muscle glycogen by consuming a high-carbohydrate diet (with more than 75 per cent of calories furnished by carbos) for three days.

After the 13-day dietary manipulations, the athletes cycled for 150 minutes at an intensity of 70% V02max and then completed a 20-kilometre time trial as quickly as possible. Compared to the normal diet, the 10-day, high-fat regime speeded performances on the time trial from 30.9 to 29.5 minutes, an 84-second improvement.

Why was high-fat eating better for performance? The high-fat preparation spared muscle glycogen during the 150-minute, pre-trial cycling; 'fat-trained' leg muscles burned glycogen at only half the rate, compared to the muscles of athletes on normal diets. As a result, there was more glycogen left over to spur a spirited sprint during the 20-K time trial.

So, should you 'fat-load' for 10 days prior to your next endurance competition? Not necessarily! The Cape Town study was carried out in a manner which gave fat-loading a decent chance to beat normal eating; your actual competitions may proceed quite differently. To be more specific, in the Cape Town research the 1 50-minute, pre-trial exertion was completed at a low-enough intensity (just 70% V02max, or about 80 per cent of maximal heart rate) so that muscles accustomed to a high-fat diet could rely on fat as their primary energy source, saving glycogen for later. You see, muscles will rely primarily on fat for energy only if the actual intensity of exercise is low enough; once intensity rises to a certain level, the muscles have to go with carbohydrate, even if they've been trained to burn fat.

So, in a true competitive situation, even for a prolonged event such as a three-hour marathon, the intensity of exercise is high enough to force muscles to draw heavily from their carbohydrate stores, even if they had been prepared to rely on fat by 10 days of fatty eating.

The bottom line - or actually the 'bottom time' - is about three hours, according to Cape Town researcher Tim Noakes. 'If your competition lasts for longer than three hours, then your average intensity of exercise is modest enough so that fat oxidation becomes important, and you can consider using the pre-race, high-fat eating strategy,' says Noakes. Such dining habits will give your muscle cells a fat fetish, which they can indulge in as you cycle or run at a moderate pace. Your glycogen stores will be more effectively preserved, and you should have less fatigue and an increased ability to push hard at the end of the competition.

So here's the overall picture. If your competition or workout lasts for about three hours or less, don't worry about putting on the high-fat feed bag. For longer efforts, 10 days of fat plus three days of carbos might give you considerably more endurance - and a new PB.

If you complete your race in 2:45 or so, why wouldn't some heavy pre-race fat consumption help you? Well, you'd be teaching your muscles to utilize fat - but then burning primarily carbohydrate during your competition. It would make your muscles schizophrenic, and it wouldn't help your performance.

('Effects of a Low-Carbohydrate, High-Fat Diet Prior to Carbohydrate Loading on Endurance Cycling Performance,' Biochemistry of Exercise Ninth International Conference, p. 32, 1994)