Fat and Carb Fuel Mix During the Marathon

With many runners coming up on their goal marathons the topic of how to handle fueling during the race is of high interest. Dr. Mark Cucuzella, MD and veteran marathoner says the body carries around 50,000 calories of fat and 2,000 calories of carbohydrates. You require 3,000 calories of carbs to run a marathon.

The key is to burn more fat which in turn preserves your carbs until you really need them, which usually is in the last 15k. So how do you burn more fat early on? You have to reduce your insulin response which happens when you ingest sugary fast carbs, which stimulates you to burn stored carbs and reduce burning of your fat. During running the blood supplies are directed towards cooling and muscles rather than digestion, so taking in carbs during a race takes some time to show an effect, usually 30 minutes.

While adapting to burning fat should be a core principle of any good training program (its fundamental to the Lydiard Method), how should one handle race day fueling given the importance of fat burning first? Here’s some thoughts to consider:

1. Dr. Cucuzzella says do not eat a high carb or sugary breakfast on race day. It will sabotage your ability to burn fat. Rather just have alight breakfast of fat/protein/carbs.

2. Research shows that ingesting simple carbs at the onset of exercise keeps your insulin high inhibiting your ability to burn fat. It causes you to burn your limited carb reserves.

3. However, there is no question that later on in the race simple carbs are of benefit when your fat reserves are low.

4. Be careful of taking in sugary drinks during the race. These will inhibit your ability to burn your fat reserves. Water is great or electrolyte replacement drinks like Ucan or Nuun which have zero calories and only critical electrolytes.

5. So, pack a few gels in your race belt, make sure they have potassium, sodium, sugars and carbs in the mix. Dr. Cucuzzella recommends 1 gel after 1 hour into the race. Then 1 each hour thereafter. Some may want to take one every 45 minutes. That’s up to the individual.

6. Be sure to test out your gel choices in a training run to be sure it doesn’t upset your stomach and so you can get an idea of how long before you feel a benefit.

For more information on the Lydiard Training Method stop by the store. We are trained, certified Lydiard Method coaches and would enjoy talking with you about it.

Bob Dyer (Co-owner, Running Niche)
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