The new rules of long run fueling
Carboyhdrates are the body’s preferred source of energy, so it’s not likely that runners will eschew pasta and cereal anytime soon, but what about our affection for Gatorade and GU? Running Shorts has discussed the low-carb approach before, but a recent Running Times article prompted me to revisit the topic.
Meb Keflezighi, Olympic medalist, 2009 NYC marathon winner, and 5th place finisher in this year’s Boston marathon often completes long runs relying only water. And he’s probably a better runner because of it. I know what you’re thinking – “Run 18+ miles without gels or Gatorade? No way! I’ll crash”. Ok, I know the idea sounds radical, but stick with me. Managing glycogen stores is one of the most basic tenents of long distance running (and all endurance sports, for that matter). Our bodies can only store about 2,000 calories of carbohydrate (glycogen) in our muscles, so if you burn roughly 100 calories an hour, you’ll run out of fuel or “hit the wall” at about mile 20. However, while glycogen is the most readily accessible form of fuel, our bodies can also turn fat into fuel if necessary – it’s just a more ineffecient process. Since we have an almost unlimited supply of fat stores – “even the thinnest runners have enough body fat to get them through 600 miles” - the trick is to get your body to rely less on glycogen and more on fat stores.
Consuming sports drink and gels over the course of a long run will increase your glycogen levels, but they won’t do much to encourage fat metabolism. Additionally, if you are sensitive to dips in blood sugar, consuming sugar may actually make hypoglycemia worse. After the initial energy boost from the sugar, your body will pump out insulin, and your blood sugar levels may crash. If you can time your fuel intake correctly, this may not be much of an issue, but wouldn’t it be better to avoid the spikes all together?
When I read about Meb’s water-only long runs, I was intrigued. Confession: I find fuel belts cumbersome and gels upset my stomach, so I often do 15-16 mile runs using only water. I felt guilty about this for a long time - was I hindering my performance? Simply being lazy about sports nutrition? Finally my habits seemed justified! It’s important to note, however, the difference between training run nutrition and race day nutrition. Running without carbs may teach your body to more effectively burn fat as fuel, but you’ll want to go in to race day with a full tank of gas (i.e. eat your bagel on race morning and don’t forget your gel). And rather than going buck-wild and doing this weekend’s 20-miler sans-GU, take a more gradual approach. You could do a few pre-breakfast morning runs or if you run doubles – refuel from your first run primarily with protein and fat and you’ll be slightly carbohydrate depleted for the day’s second workout. Most importantly, keep in mind that carbohydrate depletion is not the same as calorie restriction. You still need to fuel and hydrate your body – it’s all a matter of finding the right formula for your optimal performance!
And if you remain skeptical about running long in a carb-depleted state, there may be a middle ground. Meb recently endorsed a new sports drink called UCAN, which contains a “superstarch”. The touted benefits of the superstarch are more stable blood sugar levels and a suppressed insulin response (i.e. less glycogen and more fat burning). It’s too early to tell what effect this product will have on the running community, but nonetheless, it’s an innovative alternative to mainstream sports drinks.