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Fat for Energy
Fat for Energy
Advice directly for runners
QUESTION: I seem to be reading more and more in athletic magazines lately about fat as a good source of energy. Confusing isn't the word. Most nutritionists believe we should eat as little as possible, yet some sports nutrition researchers evidently think we need more to compete well. They both can't be right. Who is? R. Ashworth, Forest Hills Gardens, NY
ANSWER: Not the fans of fat, though the no-tion seems to have taken on a life of its own. Fat is what it's al-ways been: a useful fuel for en-durance exercise that's already so plen-ti-ful in your body it's a virtually limitless fuel.
My guess is that fat's fraudulent come-back started with a study done about ten years ago on cyclists who, after stuffing down a high-fat diet for four weeks, were able to exer-cise as much as they did previously on a normal diet, but burned much less pre-cious muscle glycogen in the process. Since glyco-gen is the fuel of choice for your muscles, every-one wants to conserve it. So if extra mayo on the cheese-burger could help shield the supply for awhile, why not?
Plenty why not. First, no group of lab cyclists exempts athletes from the fat-cho-lesterol-coronary risk equation. Second, the study was in a sense load-ed. The tests were done at relatively low exer-tion levels where the body is happy to burn fat as fuel anyway. If things had been stepped up closer to race pace, the extra-fat athletes might have run out of gas much sooner.
The answer to better long-term en-dur-ance is hoarding glyco-gen, not fat-packing. And if you never race lon-ger than about 90 minutes, you don't even have to do that: Everyone's mus-cles have at least that much glycogen squirreled away. But not many of us do a triathlon, or long cycling race, or marathon, in one-and-a-half hours. We have to pack in as much additional glycogen as we can, usually by carbo-loading, and then use it spar-ingly for fuel.
Your goal is not fat load-ing but fat burning, and there's a way to do that better. Fat is used for fuel in lower-intensity exercise, say at less than 70 per-cent of your body's maxi-mum oxygen capacity. But training exclusively at that level doesn't help the process go any bet-ter: run slow, race slow, burn fat, start it all again.
What you want is for fat to also help you at higher speeds, which means working on a boost to your oxy-gen capaci-ty, or VO2max. After all, the higher the "max" from which the 70% is fig-ured, the more fat energy you'll use in racing. An élite marathoner may zip around that 26.2-mile course at a relatively mod-est 75% of a lofty VO2max, and nearly a third of the fuel burned will be fat.
Your second strategy should be to work on your anaerobic threshold-the exercise intensity at which your body, desperate for air, stops using anything but its most efficient fuel, glycogen. At this point you're no longer burning fat, and you're also produc-ing lactic acid, a fatigue-enhancing by-product.
Books have been written on boosting your VO2max and anaerobic threshold, so we'll steer clear of that here. Just remember: Fat is not, and never was, a training aid. It's a fact of life. All you need to do is condition yourself to use it.
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