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Today, 07 November 2009

› Malema’s life in danger

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› Eskom chair faces the axe

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Yesterday, 06 November 2009

› ANCYL, BMF back Maroga

› Vanilla Ice, ice baby?

› Eskom boss 'slaughtered'

› I have fallen hard - Joost

› Eskom boss 'pushed'

It is well known that to optimise your running performance in endurance races you need to ingest carbohydrates during the race, maximise your carbohydrate stores (particularly muscle glycogen) before the race, and increase you ability to burn fat at race pace.

For some years now endurance athletes have carbo-loaded before races, knowing that their training has enabled them to store muscle glycogen more efficiently than someone who is untrained. (See Eating for exercise).

However, we also know that training increases the number of mitochondria, the energy producers in cells, in muscle, which allows better use of fat as a fuel in endurance running (see Training and muscle metabolism). Through training you can burn more fat at racing pace, so sparing your glycogen supplies.

For some time now there has been a suggestion that fat loading may improve performance. The interest in this arose when it was realised that enhanced fat utilisation may be very important since it affects how fast your limited glycogen stores are used. Is there a dietary technique similar to carbo-loading which will improve your ability to use fats while racing?

Fats and performance

Research, including that carried out at the Sports Science Institute of South Africa, suggests that there may be.

Animal studies in which the animals were fed a high fat diet for more than 4 weeks showed a significant increase in endurance performance. In some older studies on humans researchers found some indication of increased fat utilisation, but could not replicate the increased endurance performance found in animal studies.

However, recent work is more promising. A review of runners diets found that most runners are actually eating 50% carbohydrate rather than the 60 to 70% recommended anyway, so eat a higher fat diet than originally thought. These athletes were performing well. Was this in part due to their higher intake of fat?

To investigate this, researchers studied trained cyclists. They placed them on two regimes: a high fat diet (67% fat, 7% carbohydrate, 26% protein) and a high carbohydrate diet (74% carbohydrate, 12% fat, 14% protein). They then evaluated their endurance exercise performance.

Obviously those on a high fat diet had lower muscle glycogen stores than those on the high carbohydrate diet. How did each group perform?

Over short periods and at very high intensity (anaerobic type) there was no difference. However, when exercised to exhaustion differences started to appear. The carbo-loaded group took 50% longer to cycle to exhaustion at high intensities than the fat-loaded group. However, at moderate intensity, the fat-loaded group rode for 87% longer than the carbo-loaded group, when exercising to exhaustion.

So, at moderate intensities, over a long time period there would seem to be some advantage to fat loading.

Scientists are not quite sure how this is achieved. It may be that fat-loading increases the oxidative enzymes in muscles, which will allow more fat to be burnt at race pace. This is actually a similar adaptation to that found in the muscles after training. There are some who believe that a combination of a high fat diet and the correct training will increase this effect even more.

It would also seem that you can carbo-load and fat-load. Optimal fat loading probably takes around 10 days, allowing you to carbo-load for the last three days before the race. In fact another study of cyclists in South Africa showed that those who fat-loaded and then carbo-loaded in the traditional way improved their 20 km time trial by 1.5 minutes.

Tim Noakes of the Sports Science Institute of South Africa says that recent research in this centre has shown that the ability to store glycogen using carbo-loading is not adversely affected by preceding fat-loading.

To fat load or not

This is all very preliminary research, so at present it is not advisable to try this technique unless you are under the supervision of a trained exercise physiologist.

Most marathons are run at very high intensities, so fat-loading may not have any benefit at these intensities anyway. Most of the work so far has been with cycling, a different type of endurance sport.

It may be than fat-loading is most appropriate for very long races, ultra-marathons and more, and for iron man type triathlon events, not for normal marathons.

There is also the potential problem of the health risks of a high fat diet. If you are a lean elite athlete, with a very high proportion of muscle to fat, then fat-loading is probably going to be alright. However, if you are a normal weight recreational runner with a family history of cardiovascular disease, then this probably is not for you.

What this research does suggest is that elite athletes can probably eat more fat in their diets without damaging their performance. They may in fact enhance it, depending on the type of event they train for, particularly if they only increase their fat intake in the weeks before an event.

I'll keep you updated as the research continues.