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Article - 21 September 2011

Runner's World Article:The Latest on Endurance Nutrition

The Latest on Hydration, Fueling, Fat-Burning, Beet Juice, and Endurance Nutrition from the New Guy at Gatorade.

Dutch-born Asker Jeukendrup, Ph.D., once an elite road cyclist, decided to concentrate instead on sports nutrition, and has become one of the world's leading experts in the field. He has especially studied the role of carbohydrate consumption on endurance performance. Last June, Jeukendrup accepted the position of "global senior director" of the Gatorade Sports Science Institute, an arm of the Gatorade brand that conducts performance research and educates coaches and athletes. He promises that exciting new products will be coming from Gatorade. Next month Jeukendrup will compete in his sixth Kona Ironman World Championships. Last Friday, he visited us in Emmaus, Pa., to speak to the editors of Runner's World, Bicycling, Men's Health, and Women's Health.

RW: After all these years, I think many runners are still confused about how much they should drink in a marathon. What do you recommend?
AJ: It’s okay to lose about two percent of your body weight. In most situations, that won’t affect your performance. You can achieve this most of the time by drinking when you are thirsty. I don’t think this always works, but most of the time it does. I completed one Ironman where I didn’t drink much because I was never thirsty. It was a very dry day, and at the end I was nine percent dehydrated, and had a very bad performance. So paying attention to my thirst didn’t work that day. The best idea is to weigh yourself before and after workouts perhaps once a week. Learn how the weather and your pace affect your sweat rate. Then you will know what you need to do on race day.

RW: You are probably best known for your research on the carbohydrate side of endurance performance. What have you learned?
AJ: We’ve shown that the more carbohydrates you consume during the competition, the better you will perform. I don’t care if you get them from a drink or a gel. Either way, it will make a difference. Runners don’t practice carbohydrate consumption enough during their training. This is something athletes should work on. The gut is very trainable, more so than the muscles. If you push the amount of carbohydrate you take while training, you will adapt, and your performance will improve. It used to be believed that an athlete could only absorb one gram of carbohydrate per minute of exercise. That’s just 240 calories per hour–not very much when a runner could be burning 800 or 1000 or more calories per hour during a marathon. We’ve shown that it’s  possible to increase carbohydrate absorption by 25 percent if you use the right sugars, and I think we might be able to get it higher.

RW: Runners also have energy problems toward the end of marathons because they start too fast, and burn too many carbs in the early miles, is that right?
AJ: That’s right. The faster you run, the higher the percent of carbohydrates that you burn. On top of that, it’s also true that you burn more carbohydrates at the beginning of a marathon because you are fully loaded with glycogen then. As your glycogen supply drops, you burn fewer carbs. So going fast at the beginning of a marathon is a sort of double whammy. If you can stay very relaxed the first 5K or so, that is a very good idea.

RW: For the last 15 years, running magazines have published many articles warning about hyponatremia–low blood sodium–that comes from drinking too much during marathons and ultra-endurance events. And we know that hyponatremia has caused a handful of deaths. But do you think the hyponatremia risk has been overexaggerated?
AJ: Yes, I think it’s been overblown a bit. I don’t want to dismiss that it exists, and can be very serious. But in those cases where someone has died, they have been at the extreme end of the low-sodium scale. Most of the athletes who finish marathons with low sodium have no symptoms and aren’t ill.

RW: I know runners who now take a little salt before or during a marathon because they believe it might help them retain more water, prevent hyponatremia, and reduce cramping. Your thoughts?
AJ: The body has high sodium reserves, and individuals react very differently, so I’m not sure these strategies will be very successful. Perhaps a little. But I would also worry about people taking too much sodium, which could cause problems. With Gatorade, we prefer to take the approach of replacing the electrolytes you lose rather than giving you extra electrolytes.

RW: You’ve also done research on fat-burning and the fat-burning zone, something that many exercisers are interested in. What have you found?
AJ: You have to distinguish between fat-burning percents, and the total fat you burn. To burn a high percentage of your total calories as fat, the less intensely you exercise, the higher the percent of fat you burn. So you burn the highest percent when you are just sitting and doing nothing. This obviously doesn’t help someone who wants to burn more calories to lose weight and body fat as well. In this case, we have found that individual variation is very high. Some people burn the most calories when they are exercising at 40 percent of their VO2 max and some at 75 percent. For most, the optimum range is probably about 60 to 65 percent of VO2 max.

RW: Which is in the low end of the aerobic training zone for runners, right? So runners doing easy, slow workouts are exercising at the intensity where they are also maximizing their fat-burning. Is that correct?
AJ: Yes. And training improves your ability to burn fats, which can increase your endurance in long, relatively slow events. There are also people who are born as efficient fat-burners and others who are not. Training can improve your fat-burning efficiency, but it can never make you into one of the best fat-burners if you weren’t born that way.

RW: What's your view on the relationship between exercise and weight loss?
AJ: The research shows that exercise can play an important role in weight control, mainly on the side of helping you keep the weight off. The best way to lose weight rapidly is to address your nutrition, and correct the dietary mistakes you're making. The relatively rapid weight loss you get is also highly motivational–it keeps you on the program–so that's good. People can lose weight this way. The problem is, they can't keep the weight off. To me, the way forward is to put people on more gradual weight-loss programs that combine exercise and a better diet. The motivation part of this approach can be difficult, because the weight doesn't necessarily come off quickly. So we need to do a better job telling people about all the other health improvements that come with regular exercise–better blood pressure, lower diabetes risk, lower heart disease, and so on. We have to explain that it's a slow, long-term process that has many long-term benefits.

RW: There’s an endurance-training technique sometimes called “Train low. Race high.” It suggests that athletes should sometimes do their long training runs while glyocogen-depleted, rather than glycogen-loaded, which is what they would do in a race. So far the results of studies have shown changes in certain physiological measures, like more fat burning, but not so much in actual performance. Your take?
AJ: I think if the physiological changes are there, the performance must ultimately follow. I think the studies thus far have not been well-enough designed to show the performance improvement, and that includes studies from my lab. I think none of us have tested our subjects in a long-enough trial after they have gone through the protocol.

RW: So you're saying that you think the "train low" approach might work?
AJ: Yes, but I would take it even farther. I would say you should train low and long perhaps once a week, and also train high and fast once a week. In other words, do one long run a week in a low-glycogen condition and don't take any carbohydrates. But also do one fast workout where you are glycogen-loaded and take carbohydrates during the workout. That way you are doing one workout to improve your fat-burning and one workout to improve your carbohydrate-burning. You are training both systems.

RW: Some of the most interesting studies of the past year have indicated that a day or two of beet juice consumption can improve endurance exercise results quite a bit. The studies have attracted a fair amount of attention because they've been done by good researchers from good labs. Can you explain these results?
AJ: No I can't explain them. I don't know the mechanism that would cause them, and that bothers me. It also bothers the scientist who has done much of the work, Andy Jones, who is very good as you say. But he also can't figure out why the beet juice is enhancing endurance.

RW: I imagine you've tried it yourself?
JA: No, I haven't. I'm waiting until I can set up a controlled trial, and then I'll try it.

RW: Do you think the East Africans run great distance races because they have the best diet?
JA: No, I don't think it's the diet. Many of them have a sub-optimal diet if you look at the studies that have been done. I think they probably have a biomechanical advantage. It could be their skinny calf muscles, as some researchers have pointed out. But having said that, I also believe that life in Ethiopia is just so different from the developed world. They might just have a different perception of perceived effort and discomfort. They might have a higher pain tolerance. I was there at one time when Gete Wami had an Achilles tendon injury so bad she could barely walk. And yet she would go out and do the marathon workouts with the group as if nothing was wrong with her Achilles. So I believe the East African success story is based on a combination of factors, including their lifestyle.

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