For as long as I can remember- from the first time I set foot in a gym, actually- I’ve been listening to folks debate the question…
“Should I eat before I exercise?”
Now a new study may finally shine some light on the matter. Researchers found that exercising on an empty stomach has several beneficial effects, including preventing weight gain and maintaining insulin sensitivity.
Researchers in Belgium took 27 healthy young men and fed them all a horrible diet, high in sugar and fat and calories. The particular diet was chosen because it was just about guaranteed to create both weight gain and a reduction in insulin sensitivity.
Insulin sensitivity, you may remember, is something good- it’s when the cells respond well to insulin, meaning that insulin does an excellent job of removing excess sugar from the bloodstream and getting it into the cells where it can be “burned” for energy. When someone is said to be insulin resistant on the other hand, this system doesn’t work well, and the person winds up with high blood sugar and high insulin and is on the path to either metabolic syndrome or diabetes. Most diabetics are insulin resistant, and most people who are insulin resistant are overweight, since insulin “shuts down” the fat burning process.
In the Belgian study, the researchers divided the men into three groups:
- One group did nothing but eat the terrible diet (the control group). This group didn’t exercise at all during the study.
- The second and third group did exercise, and did the exact same workout;
- but the second group did it after breakfast and the third group did it before breakfast, exercising on an empty stomach.
The results were both surprising and dramatic.
The control group- not surprisingly- gained a lot of weight and also saw their insulin sensitivity plunge (meaning they became much more insulin resistant). The “exercise after eating” group also gained weight, but not nearly as much as the control group. And their insulin sensitivity went down, just as it did in the control group.
But the “exercising on an empty stomach” group was a whole different story. This group- despite eating a perfectly horrible, weight-gain inducing diet- did not gain weight. Not only that, their insulin sensitivity remained high and the bad diet did not make them insulin resistant. “This study for the first time shows that fasted (empty stomach) training is more potent than fed training to facilitate adaptations in muscle and to improve…. glucose tolerance and insulin sensitivity…” said the study’s authors.
Conventional wisdom- which is not always so wise—has held that it’s always best to eat something before working out. Proponents of this way of thinking would always point out that you need “energy” for working out, energy which comes from—what else?—carbohydrates. “Fat burns in a flame of carbohydrate” they’d proclaim solemnly.
Problem is, the conventional wisdom is wrong.
It’s interesting that back in the days of “Stay Hungry” and “Pumping Iron” when the big meccas of bodybuilding like World Gym and Gold’s Gym in Venice were home to such legendary bodybuilders as Arnold Schwarzenneger, Lou Ferrigno and Franco Columbo, everybody exercised on an empty stomach. Bodybuilders of that era believed that you were more likely to mobilize your fat stores for fuel if you didn’t have to burn off a whole bunch of carbs that you just scarfed down for breakfast.
We now know that they were mostly right.
So should you forgo eating before working out? Not necessarily. “If you’re interested in performing better- like if you’re training for an event—you might want to eat first”, says my friend exercise physiologist Liz Neporent, MS, CSCS, author of “Fitness for Dummies”. “But for weight loss, evidence does seem to be trending towards not eating before working out”.
Neporent points out that as a practical matter, there are going to be a fair amount of people who don’t do well when they don’t eat before working out. “They get dizzy, sick, and even faint sometimes”, she told me. “But I’ve also had people eat right before working out that have felt exactly the same way!”
Bottom line, it’s going to be- like everything else- an individual thing and no one prescription is going to work for everyone.
But for those who want to try it- and who don’t get lightheaded or dizzy- exercising on an empty stomach might be just the thing to stop weight gain in its tracks. It did in the Belgian study, and those folks were purposely eating a really bad diet. It should work even better if you also couple it with a diet designed to help you reach your goals.
Watch this funny little video where I reveal my 5 favorite fat burning snacks that won’t trigger a high insulin response.