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Articles March 2017 Issue

Smart Pre-Exercise Snacks

Make sure you're properly fueled for a workout, but avoid mindless snacking.

If you start exercise low on fuel, you could end up feeling weak and run out of steam. Or, you may simply feel hungry, making it hard to focus on your exercise. However, unnecessary snacking before a workout may make exercise uncomfortable and add calories you don’t need, counteracting the calorie burn of your physical activity.

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What you’re already eating for meals and snacks likely covers your exercise energy needs.

"I think there's a misconception that you need to eat a snack before exercise, but this is generally only necessary if it’s been at least 2 to 3 hours since your last meal," says Jennifer Sacheck, PhD, an associate professor at Tufts' Friedman School who specializes in physical activity research. "For example, if you eat lunch at 11 a.m. and are going to the gym at 5 p.m., or you exercise first thing in the morning, you’ll need to refuel before exercise." However, if you ate a late lunch at 2 p.m., and you’re working out at 4:30 p.m., you shouldn’t need a snack first.

Timing Snacks:

Munching a snack while you head to the gym may not give you the benefits you're seeking. "People sometimes eat too close to exercise," Sacheck says. "Eating 15 minutes before exercise is not ideal." She explains why:

- Your snack won’t have time to be digested and absorbed, so its energy won’t reach your working muscles during exercise.

- Blood flow will be diverted to your gut instead of increasing to arm and leg muscles to fuel movement.

- Undigested food sitting in your stomach may cause discomfort and interfere with more intense cardiovascular (aerobic) exercise, such as running or swimming laps.

On the other hand, a well-timed snack can help fuel exercise. According to the American College of Sports Medicine, when you consume a carbohydrate-rich snack within 1 to 4 hours before exercise, it can help replenish liver and muscle glycogen - the storage form of glucose, which is the main fuel for working muscles. It also can stabilize blood sugar levels, which helps fuel the brain and central nervous system. This helps keep you mentally alert during exercise.

Choosing Snacks:

Carbohydrate-rich foods should be the main focus of pre-exercise snacks but should be balanced with protein and fat. "Including a bit of protein, fat and/or fiber in a carbohydrate-rich snack helps with satiety and helps prevent a big blood sugar spike followed by a drastic fall during exercise," Sacheck says. The addition of protein to snacks eaten before resistance exercise (strength training) also may promote muscle recovery after your workout.

Low-fat yogurt, cheese sticks, nuts, seeds and canned seafood in single-serve packs are quick sources of protein and healthy fat. Opting for whole grains or whole fruit is an easy way to get carbohydrate with fiber.

Selecting Snack Size:

"In general, the closer you are to your workout time, the less you should eat and the more you should limit fat, protein and fiber, so the snack will be more quickly digested and absorbed," Sacheck says. This is particularly true before intense cardiovascular exercise as opposed to a moderately-paced walk or resistance exercise.

If it is 2 hours or more before exercise, Sacheck recommends a snack with 200 to 300 calories, depending on your individual needs. Snacks eaten 1 hour before exercise generally should be simpler and lighter - typically 100 to 200 calories.

If you have just 30 minutes before exercise and need a snack, you may do OK with a small piece of whole fruit or other quickly-digested carbohydrate, such as whole-grain pretzels. Fruit is high in water, so it also contributes to hydration. Skip sugary sports drinks; opt for water to hydrate before exercise.

So, avoid unnecessary snacking, but if your energy lags during exercise, a smart pre-workout snack may give you a boost.

To learn more: Medicine & Science in Sports & Exercise, March 2016

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