Skratch Labs found Dr. Allen Lim gets questions about training on a pretty regular basis. One of the most common is "How do I fuel for an ultra?". Well, here's his answer!


First and foremost, fueling for an ultramarathon begins well before the event. At least 10 days before the race, carbohydrate intake needs to be increased to up to 70% of total fuel intake to ensure that carbohydrate stores in muscle (i.e., glycogen stores) are maximized. For many, this may require up to 7-8 g of carbohydrate per day for every kilogram of body weight. Accordingly, a 70kg (154 lbs) individual may consume as much as 480 to 560 grams of carbohydrate (1,960 to 2,240 Calories) each day in the week leading up to an event. Since stored glycogen also stores extra water, expect a few pounds in weight gain coming from both stored carbohydrate and an increase in water weight. 

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On race day it’s important to get some food in the stomach at least 2.5 to 3 hours before race start. Something simple like oatmeal and eggs or rice and eggs typically works very well. During the race, distinguish between hydration versus fueling, especially if you're prone to gastrointestinal distress. 

For hydration, drinking Skratch Labs Sport Hydration Drink Mix at normal concentration (1 scoop per 16.9 ounces of water for 80 Calories & 800 mg of sodium per liter) or up to double concentration (2 scoops per 16.9 ounces of water for 160 Calories & 1600 mg of sodium per liter) to thirst is the best strategy. Because Skratch Labs Sports Hydration Drink Mix contains a sodium profile that better matches what’s lost in sweat for the general endurance population, thirst - which is driven by changes in blood sodium - becomes a much better gauge for maintaining both water balance and electrolyte balance than when drinking plain water or something with inadequate sodium. 

For fuel, try and stick with solid foods if possible, especially earlier in the race so that the stomach can be used as a reservoir for energy that then slowly and consistently trickles energy into the small intestine where it is then absorbed into the body. Typically, gastrointestinal distress or “gut rot” occurs when fuel empties from the stomach at too rapid of a rate and when that rate exceeds the small intestine’s ability to absorb that fuel. By using real food over an excess of highly concentrated liquid carbohydrates to balance fueling, energy levels stay more consistent and the risk of gut rot is diminished. With this in mind, beginning in the first hour of excess your goal is to consume at least half the calories that you are burning or between 40 to 80 grams of carbohydrate per hour. Remember, that per 16.9 ounces serving of Skratch Sports Hydration Drink Mix that there is already 20 grams of carbohydrate. 

A number of portable recipes for fueling on the go can be found in the Feed Zone Portables Cook Book along with additional advice to help fuel for your ultra marathon. 

- Dr. Allen Lim