Exercising and Eating

When is the best time to work out: before or after a meal?

Q. I try to walk 1.5 miles every day on my lunch hour. Is it better to walk before or after I eat?

A. It’s a good idea to eat or snack on something before a workout to provide a little bit of fuel. But if you’re only walking, and only for 1.5 miles, or a 30-minute walk, you probably don’t really need to specifically fuel yourself up for this level of activity, unless it’s been more than three or four hours since you last consumed any calories.

Some people worry that they shouldn’t eat before they exercise because they’ll interfere with their digestion and/or get cramps. There’s some truth to this—when you chow down, blood vessels in your digestive system expand, shuttling more oxygen to assist with the digestion and absorption of food. This shifts some blood away from other areas of your body. When you exercise, blood shifts to muscles to provide more oxygen and energy.

So if you’ve triggered both of those systems, which one is favored to get the increased blood flow?

It depends on how much you eat and how hard you exercise. Typically, the body’s energy needs are addressed first. So, especially if you are doing a vigorous workout, circulation to your working muscles increases and digestion slows down.

Whether you experience gastro-intestinal discomfort depends on what and how much you eat. If you eat a large feast or high-fiber foods, you may get cramps, especially if you are doing an activity that jostles that partially digested food around in your gut, like playing basketball or other activities that involve jumping.

That doesn't mean you shouldn't eat before intense workouts; you should just eat less, and eat (or drink) more easily-absorbed foods (such “bad carbs” or high-glycemic foods such as juice, pasta or sports drinks.) A 2002 Penn State University study gave regular runners who normally did not eat before they exercised 100 calorie snacks—either a banana, an energy bar or dried fruit (prunes). Then they ran three miles. No one got cramps and all reported feeling more energetic.

If you are doing a low-impact, and low-to-moderate intensity workout, like walking, you probably won’t have any problem eating beforehand, even if it’s a big meal.

But, if you are going to indulge, especially in a high-fat meal, it might be a better idea to walk or exercise beforehand. Think of your walk as a potential fat-blocker, and a way to help boost the ability of your body to handle the excess calorie load.

Several studies have found that exercising at various intensities helps metabolize fat in subsequent meals, some as late as the day after the workout. A 2002 study in the journal Medicine & Science in Sports & Exercise had normal-weight women ride a bike and burn about 300 calories during the session. Thirty minutes after the session they were given a liquid high-fat meal. Researchers found that the exercise boosted their ability to oxidize, or burn some of the excess fat, and this was above and beyond what they might already expect to see from a post-exercise increase in metabolism.

If you want to bump your walk up to a jog before lunch, you might get an even greater effect. A 2001 study in the International Journal of Obesity suggests that higher-intensity exercise produces greater post-exercise increases in fat oxidation than a lower-intensity workout.

It’s well established that regular exercisers tend to be leaner, and the ability of daily workouts to regulate excess fat intake in this way may be one way that exercise can help reduce a positive fat balance, and ultimately weight gain.

Reproduced from MSN Health & Fitness By Martica Heaner, M.A., M.Ed.