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Training on empty is a strategy for burning fat at any cost; it torpedoes performance, burning the fat in the muscles--and the muscles themselves.
Training on Empty—Still a Bad Idea
It was all over the Internet and in newspapers across the country, perhaps the world. A UK study apparently found that training while fasting burns more fat. I say “apparently” because we were unable to find the study in the April issue of Medicine & Science in Sports & Exercise, as AP writer Maria Cheng reported. Be that as it may, the article is detailed and balanced, with comments from experts on both sides of the issue, giving us plenty to analyze.
We believe training on an empty stomach is a bad idea.
Why is explained in an earlier piece on our FAQ page: http://cbass.com/Faq2.htm#Training
I wrote there that I plan to continue eating a pre-workout snack--until I hear an “authoritative opinion to the contrary.” I suppose that qualification has been met. So, let’s talk about it.
“In a study published in April,” Cheng wrote, “researchers at the University of Birmingham and elsewhere assigned seven people to cycle three days a week, followed by an intense session an hour later without eating. Another seven people followed the same regime, without the instruction to fast.”
Those that fasted burned “significantly more fat,” according to Cheng. We are not told how much more.
There’s a catch, however, again according to Ms. Cheng: “The group that didn’t eat performed worse on the intensive training.” (Emphasis added.)
Dropping performance is a major motivation killer--capacity for high-intensity exercise disappears without carbs--a very bad thing for long-term trainers. That's important because you’re not likely to keep doing an activity you find unpleasant. Who wants to keep doing something that adds up to a drag on performance?
Dr. Richard Winett, an expert on the psychology of training, agrees: “It's hard to perform well when you're hungry, so that's a detriment.” He questions whether the results justify the discomfort: “The data suggests that whatever greater fat loss may come through this approach is very small, and more easily achieved by more healthful [means].”
Ron Maughan, a professor of sport, exercise and health sciences at Loughborough University in Britain, disagrees, at least in part.
“Science is finally catching up with what smart runners have always known,” he told Ms. Cheng. “If you have a long, hard run without breakfast once a week, that hard run will train you to burn fat—and for the rest of the week [you can] have plenty of carbohydrates so you can train hard.”
Maughan agrees on the downside: “Without enough fuel, you won’t get the intensity of training you need to get improvements.”
Others consulted by Ms. Cheng agree with Winett and me that skipping the pre-workout snack is unwise.
“I think it’s actually a pretty bad idea,” Dr. Alexis Chiang Colvin, a sports medicine specialist at Mount Sinai Hospital in New York, told Cheng. “If your blood sugar is low, you could wind up getting dizzy and you might not be able to exercise as well as if you were well-nourished.” She also warned that not eating might make people more prone to injury and delay recovery.
Peter Hespel, a professor of exercise physiology in Belgium and generally in favor of training on empty (see below), pointed out another potential drawback: “When you postpone breakfast to exercise, it is possible you might eat more afterward.” Being tired and hunger is not conducive to controlled eating.
We’ve already painted a pretty bleak picture of training on empty, and we have yet to confront the physiological facts.
Cannibalize Your Muscles
“When you exercise [without eating], fat is broken down more quickly in the muscle,” Andrew Greenberg, director of the Obesity and Metabolism Laboratory at Tufts University, told Maria Cheng. “You may enhance how you burn the fat in the muscles, but it doesn’t affect your overall body fat.” You’re not likely to see the results in your six-pack.
The other physiological downside is more distressing. Professor Hespel and his colleagues found in a 2008 study that men who did endurance training without eating experienced “a spike in the amount of proteins needed to process fat, meaning their bodies had been primed through fasting to burn more fat.”
A spike in blood protein signals that muscle is being broken down to amino acids on the way to making glucose, which must be present to burn fat. (More on this momentarily)
I explained the need for glucose to fuel the brain in my earlier FAQ. I’ll give the short version here, because it also explains why fasting leads to the breakdown of muscle tissue.
Your brain operates exclusively on glucose (blood sugar) for energy; it can’t function properly without glucose. Your body is programmed to maintain your blood sugar level no matter what the cost. Glucose cannot be supplied from fat; it must come from the breakdown of carbohydrate or protein.
Glucose made from carbohydrate circulates in your blood and also resides in your liver. (The glycogen/glucose in your muscles provides energy to your muscles, but not your brain.) If you fast over night and don’t eat in the morning, the glucose in your blood and liver is soon used up. Your brain has to get it from protein.
After blood glucose and liver glucose (glycogen) are used up, the body turns not to fat tissue, but to protein to maintain the blood glucose level. The mechanism is called gluconeogenesis, the manufacture of new glucose. Your liver does the job. It strips the nitrogen from body protein to form glucose. In other words, protein from skeletal muscles and other body structures is used to maintain your blood glucose level.
As Hespel and his colleagues observed, the protein (amino acids) in your blood spikes. That means your body has switched to converting amino acids—from the breakdown of muscles and other tissues—to supply energy to your brain. (Glucose from carbs has already been used up or isn't adequate.)
And there’s another—very important—factor to consider. We touched on it above.
“In order for your muscles to burn fat…, [glucose] has to be present,” Chris Carmichael explained in Food for Fitness. If you don’t eat before you exercise, you may burn more fat, but you’ll have to burn muscle to do it.
In summary, training on empty is a strategy for burning fat at any cost; it torpedoes performance, burning the fat in the muscles—and the muscles themselves.
If that makes sense to you, go for it.
I’m going to continue having a Tiger’s Milk energy bar and a cup of skimmed milk—or milk and an apple—before workouts.
(See also our article on the metabolic footprint of exercise: Go )
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