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Nutrition for Endurance

"It is my opinion that either too many calories or too much fluid (or both) cause 90% of the gastrointestinal problems athletes experience during endurance events." - Bill Misner, Ph.D. Nutrition Guru for E-CAPS & Hammer Nutrition

I heard from Fast Frank who just finished his marathon in a disappointing time. He 'carbo-loaded' for the event. Though his prep went well, race day did not. He said he felt heavy and bloated on race day, and had to stop more than once with GI distress. Carbo loading is a technique where you attempt to deplete glycogen reserves early in the training phase with a limited carb diet, then load carbs late during your taper. The goal is to begin your race with super-saturated glycogen (the stored form of carbohydrate) reserves for maximum fueling to carry you through.

Carbo-loading is conceptually appealing, but not effective in practice. The consensus among exercise physiologists is that we can store enough glycogen to take us through 2 to 2.5 hours of high-intensity work (85-93% of max heart rate) before our reserves are depleted. If you're an elite level marathoner, this gets you through, but the rest of us mortals need the remaining 30 to 120-minutes of running to flow with good energy.

The problem with carbo-loading theory is that our bodies can only store a finite amount of glycogen; in fact we're training it to do so every day. From 30 years of endurance racing experience I know I can't trick my body into a glycogen surplus. Loading calories beyond what we need for each day's activities just goes to fat once glycogen storage is maxed-out. Toeing the line for a marathon 'carbo-loaded' will probably just make us heavy, bloated, and maybe a pound or two heavy. Not a good way to start race day!

What does work to maximize glycogen storage is to always consume carbs within 30-minutes after a workout while the craving is strong.

As we taper for an important race day, chances are we have a calorie surplus. Fewer calories are used during a taper, yet eating at your regular full training consumption rate creates the surplus. If we reduce training for 3 to 5 days pre-race while maintaining typical training-day consumption, we can easily gain a pound or two by race day—not a good thing except perhaps for an IM race day where the extra weight should be gone by start of the marathon.

So if we can't pre-load calories to keep us going beyond 2.5 hours, how do we get through a 140.6 mile Ironman event without bonking? The answer is we race an Ironman at lower energy levels where both glycogen and fat is burned simultaneously in addition to any calories we can absorb during the race. Near AT (anaerobic threshold)/LT (lactate threshold) levels we use primarily glycogen to fuel our ATP (adenosine-tri-phosphate) needs. When we exercise at lower levels we can use a higher proportion of fat (which goes through a more complicated and slower process to become useable energy) along with glycogen as fuel. At appropriate levels for an Ironman distance event (65 to 75%HR), we can derive 50% or more of our energy from fat to get us through. Even the leanest of us has enough fat (3250 calories per pound of fat) to get us through an Ironman.

For those of you that have raced and Ironman, you know a successful race day is dependant upon getting nutrition dialed-in.

I recently coached an athlete through her first Ironman and she insisted on bringing 3 peanut butter and jelly sandwiches along with various other snacks, gels, and hydration products. She finished the ride still carrying 2.5 PBJ sandwiches, and even without her PBJ calories she had plenty of energy to finish in control!

The average athlete can consume only 250 (maybe 300 if you're 170lb+) calories per hour during an Ironman competition. This could be one small water bottle with full dilution of a hydration solution and 2 gels, or on a hot day it could be 2 bottles and one gel. Most first-time IM athletes are panicked when I tell them this is all they should consume—but it works along with proper pacing.

The sweeter the solution, the slower it's absorbed. When the contents of your stomach are sloshing, you should go to 100% water for a while until absorption gets back to a normal rate. You can finish an Ironman distance event bonked with not enough carbohydrate calories coming in, but you can't finish an Ironman dehydrated (lost more than 3% of your body weight). For my own events I dilute the hydration solution with more water than recommended to speed absorption and appease my sensitive stomach.

Keep in mind that you need to consume salt in addition to water and calories to avoid hyponatremia after several hours of steady exercise. All the water consumed dilutes the salt level within your cells, to the point where osmosis (water moving from area of lower molarity [greater dilution] to greater molarity [less dilution]) slows or stops. When this happens you're in serious trouble, and the only solution is supplemental salt intake for races over 4-5 hours duration. The more water you drink, the more salt you'll need. Experiment during long workout in training.

Getting back to my disappointed marathon competitor...his race would have gone well with the same taper, no carbo-loading, and perhaps 2-3 gels along with a sufficient amount of straight water picked-up along the course!