Are Fats Optimal Fuel For Endurance Athletes?

The marathon and triathlon seasons are fully underway and this year over half a million people will complete the marathon and thousands more participate in triathlons and other endurance events. Whether they’re entering an event for the first time or trying to achieve a personal best time, one of the most common questions I get asked by clients is “what should I eat before my long run?” The answer may surprise you!

A common refrain amongst most endurance coaches is that you must consume a heavy carbohydrate meal before your long run or bike to perform your best. High carbohydrate breakfasts of oatmeal, cereals, and juice or the classic ‘carb-load’ pasta dinner are staple recommendations from many top endurance coaches. While this is certainly not bad advice, there is another option.

Don’t eat any carbs before your long run or ride! (Yes, you heard me correctly.)

Let’s take a moment for a quick physiology review. When carbohydrates are ingested they are preferentially burned for fuel and provide 4 calories per gram of energy. When fats are ingested, or burned from body stores, they provide 9 calories per gram of fuel. You are effectively doubling your fuel efficiency if you use fat are your primary fuel source from the outset.

By maximizing your capacity to burn fat for fuel, you’ll also be sparing precious muscle glycogen, the carbohydrate stores in your muscle. You have approximately 500g of glycogen stored primarily in your muscles (and some in your liver) that can provide you with 2,000 calories of energy during your race. In contrast, even lean individuals between 7-14% body-fat have 20,000-30,000 calories available for energy use in their fat stores. Wow! That’s a lot of fuel that could be used, if you changed your pre-race food choices.

Skeptical? I don’t blame you, but the preliminary results are impressive.