Unhealthy Weight Loss Through Endurance Training

The NYT published the article “Slimmer Doesn’t Always Mean Fitter” last week which brings up the very important topic of weight loss and endurance training. It discusses the quite common practice among endurance athletes of cutting more and more weight in favor of achieving a faster PB (personal best) – the idea being less body mass = faster racing results.

This folly is actually quite common, unfortunately. I’ve listened to many serious runners tell me about how they need to “cut more weight to qualify for Boston.” In fact, I recall one particularly emaciated woman who switched to a vegetarian diet and stopped strength training altogether because she didn’t want to “bulk up.” And while this certainly helped her lose weight, it also harvested most of her lean muscle tissue and required her to adopt a high-carb (read high sugar) diet to fuel her “PBs.”

And while this is a rather extreme example, here’s an excerpt from the article that highlights the phenomenon:

When Dr. Tarnopolsky was in graduate school, he saw the delicate balance between losing just enough and too much. He and his friends would experiment, losing or gaining a few pounds and testing their VO2 maxes, a measure of the body’s ability to get oxygen to muscles during exercise. In theory, the less you weigh, the higher your VO2 max should be, relative to body weight.

Dr. Tarnopolsky said that he got his best VO2 max — 86 milliliters of oxygen per kilogram of body weight — when he weighed 156 pounds. “Like everyone else, I said, ‘Maybe if I drop some body fat, it will go higher,’ ” Dr. Tarnopolsky said. So he got his weight down to 152 pounds. But to his surprise, his VO2 max decreased, to 82.

The likely reason, he said, was that he had reached a point where his body began burning its own muscle protein for fuel. He was weaker, and his performance was worse, even though he weighed less.

The key is, when you lose weight while endurance training there is a point of diminishing returns. And once you start burning lean muscle tissue and becoming a “glucose junkie,” you know you’ve passed it.

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