Which Comes First, Cardio or Weights_ - Alex Hutchinson [76]
But there’s a more fundamental problem with the fat-burning idea, relating to how your body recovers after physical activity. If you burn mostly carbohydrates during a workout, the calories you consume in the hours after the workout will be used to replenish your depleted carbohydrate stores. If you manage to rely more on fat during the workout, on the other hand, your carbohydrate stores will remain full. As a result, whatever calories you consume afterwards will be stored directly as fat, undoing your fat-burning efforts.
This phenomenon was demonstrated in 2010 by researchers at the Garvan Institute of Medical Research in Australia. In mice that were genetically altered to burn fat instead of carbohydrate, unburned carbohydrates were simply converted into fat for storage. The total “energy balance” remained unchanged, and the mice gained or lost the same amount of weight as normal mice under the same conditions. The results serve as a warning not to waste your time and money on pills that claim they enhance fat-burning, according to Greg Cooney, the study’s senior author. “Our data urges a correction in people’s concept of a magic bullet—something that will miraculously make them thin while they sit on the couch watching television,” he said.
So far, the only technique that reliably boosts the proportion of fat you burn is—you guessed it—exercise. After a few months of training, studies have found that you will indeed burn more fat at a given level of intensity than you did when you were out of shape. Of course, while that may help you stay fueled in the late stages of running a marathon, it doesn’t really matter for weight-loss purposes. The only thing that counts is how many calories you burned to get there.
Won’t exercise make me eat more and gain weight?
In 2009, Time magazine ran a cover story called “Why Exercise Won’t Make You Thin,” in which journalist John Cloud described his unsuccessful attempts to lose weight through exercise. Cloud’s central theme, supported by his own fondness for post-workout blueberry bars and a rather selective sampling of research, was that exercise actually makes you hungrier. As a result, he warned, “fiery spurts of vigorous exercise could lead to weight gain.” The twisted logic that led to this conclusion was widely condemned by obesity researchers—but it did raise an important question. After all, it’s undeniably true that many people exercise diligently without losing weight. And exercise does make you hungrier.
Some simple math illustrates what you’re up against. Let’s say you go out and bike six miles in about half an hour, then chug a typical recovery shake. You’ve burned about 280 calories and immediately downed 270 calories—so you haven’t accomplished much. The number of calories burned through casual exercise almost always corresponds to a surprisingly small chunk of food. That means dropping weight is not an easy process. But there’s no evidence to suggest that exercise actually causes you to gain weight.
It’s true that increasing your physical activity levels can make you feel hungrier, but the same is true of eating less. Your body will respond to any change that results in you taking in fewer calories than you burn with a series of physiological and behavioral tactics that conspire to keep you at your current weight. That’s why almost none of the weight-loss interventions that have been tested in clinical trials achieve losses that the majority of participants sustain beyond a few years. It’s not just exercising to lose weight that’s hard—it’s losing weight by any means.
Of course, there’s no debate that elite athletes drop pounds and keep them off through exercise. In fact, for long-distance runners, swimmers, and Tour de France cyclists, eating enough to meet their caloric needs is a constant challenge. So it’s clear that exercise really can help you lose weight—the only question is how much. A recent Harvard University study offers some clues. Researchers followed 34,000 middle-aged women for 13 years, monitoring their diet, exercise, and weight and reporting