Should runners eat fat or carbohydrates?

For years, nutrition for sports has always emphasised carbohydrates. But could a high fat diet also be good for performance?

In the last few years, the diet world has undergone a seismic shift which is only now just beginning to filter down from the dietetic world to everyone else. This is mainly that the emphasis on eating low fat foods as the best way to lose weight has been essentially wrong.

Why? Because it has meant that people rely on low fat foods, which are often packed with sugar, and have a diet heavy on carbohydrates, which when not used up, are stored as fat. Ergo, a worldwide obesity crisis.

Now this same shift is being felt in the sports world, where for decades, the belief has been that you should fuel performance with carbohydrates.

A  huge sports nutrition industry is built upon it with the global sports drinks market estimated to be worth 52 billion dollars by 2016. With this much at stake, doubtless we may be about to experience an onslaught of studies attempting to ridicule the fat as fuel debate, with companies such as Gatorade, owned by Pepsi, or Lucozade, owned by GlaxoSmithKline, perhaps weighing in on the debate.

But the debate is hotting up as more and more athletes and exercise scientists begin to investigate using fat as fuel. A few weeks ago, a documentary funded by a Kickstarter campaign, Run on Fat, was released in the UK.  And just last week, the American Dietary Guideline Advisory Committee released advice which appeared to suggest that cutting back on starchy carbohydrates and consuming more fats and fat-rich foods improves metabolic health.

But what of the actual benefits for runners and cyclists, outside of better health?

An article by The European Journal of Sport Science published last year noted that even the leanest marathon runner has ‘in excess of 30,000 kilocalories’ in fat reserves. To put this is context, this is GREATER than the maximum amount of carbohydrates the body can store.

In other words, we carry enough fuel in the form of body fat to get us through not just one marathon, but MULTIPLE marathons.

The difference however is that carbohydrates, stored in the body in the form of glycogen, are easy to access. It provides a fast sugar buzz that both physically, and psychologically, make you feel as if you are getting the fuel you need.

Fat however, must be broken down into fatty acids before it can be used by the muscles.

Exercise scientists have already established that endurance training, favoured by marathon runners, enduro MTB riders and triathletes, enables athletes to better use fat as fuel. But can you train an athlete to rely almost exclusively on fat by removing carbohydrates?

This is the question that exercise scientist, Jeff Volek, has been studying at the Department of Human Sciences at The Ohio State University in Columbus, the results of which will be released this summer.

‘Early humans, hunter gatherers were quite physically active and primarily ate fat,’ he explains.  ‘It’s been the main fuel for active humans far longer than carbohydrates.’

According to Volek, the ideal high fat diet for sports performance would consist of 85% fat and almost no carbohydrates.

This would lead to a condition known as ketosis, whereby the body creates molecules called ketones, that result in the breakdown of fat into fatty acids. The body is then able to burn these as fuel. An added benefit is that ketones are also believed to help in the reduction of inflammation.

As of yet, no study has actually proven that a high fat diet will enhance sports performance, only that it enables endurance athletes to better use fat as fuel.

It also results in weight loss, applicable for both athletes and the general populace who seek to drop the weight for performance or life reasons.

For many recreational marathon runners, let alone general exercisers, the lesson to take home from this is DON’T consume so many (or any, if you are a general exerciser) sports drinks or gels. The more you do so, the LESS efficient your body will become at burning fat as fuel.

As for the serious athlete? It is up to you to investigate for yourself and what works for you.

With two marathons and a coast to coast event to train for this year, I have been experimenting and will continue to do so all year. I have NEVER used gels or sports drinks but have used jelly sweets to fuel long endurance runs. I’ve already begun to experiment with fuelling by nuts alone but there is a long way to go yet.

You can follow this experiment at my alternative blog 

How do YOU fuel your long marathon runs? Carbs or fat?