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Figuring out exactly how much to eat and drink during a workout can be like trying to communicate to your beloved how much you appreciate the dinner he cooked but aren't quite so thrilled about the gargantuan mess he left behind: a delicate balancing act. After all, you want to stay energized and hydrated, but you certainly don't want to cancel out all of those hard-burned calories!

Luckily, we've got the expert to show us the way: Natalie Digate Muth, MD, who, in addition to being a registered dietitian, is also a physician, personal trainer, and spokesperson for the American Council on Exercise. Check out her savvy tips, then find your ideal fuel-up formula in the chart below.

  • Exercising for 30 minutes or less? No need to eat or drink anything special while you sweat.
  • When choosing a workout bar, chews, or gel (any of the three will work just fine), pick one with easily digestible carbs—in other words, low in fiber. Your body needs to be able to turn those carbs into energy quickly, not spend precious time and energy breaking them down.
  • To keep your tummy from feeling grumpy and overloaded, divide the bar, chews, or gel so you're eating a small amount every 20 to 25 minutes.
  • Trying to lose weight? It's OK to eat a little less than the chart recommends.
  • But don't skimp on the sips! It's crucial to make sure you're replacing the fluid you're losing through perspiration, especially in these steamy summer months. Depending on how hot it is and how much you sweat, you may need more (or less) than the amounts recommended below, so let your thirst be your guide.
  • For our favorite workout bars, chews, and drinks, check out our 2011 Gear Awards.

 Length/intensity of  workout  What to drink  What to eat
45 minutes, moderate 3 ounces of water every 15 minutes Nothing
45 minutes, vigorous 5 ounces of water every 15 minutes Nothing
60 minutes, moderate 3 ounces of water every 15 minutes Nothing
60 minutes, vigorous 5 ounces of water every 15 minutes Nothing
90 minutes, moderate 3 ounces of mixture made of 75% water and 25% sodium- and potassium-containing sports drink every 15 minutes Workout bar, chews, or gel containing 45 g easily digested carbs
90 minutes, vigorous 5 ounces of water/sports drink mixture (see details above) every 15 minutes Workout bar, chews, or gel containing 55 g easily digested carbs
120 minutes, moderate 3 ounces of water/sports drink mixture (see details above) every 15 minutes Workout bar, chews, or gel containing 80 g easily digested carbs
120 minutes, vigorous 5 ounces of water/sports drink mixture (see details above) every 15 minutes Workout bar, chews, or gel containing 100 g easily digested carbs
180+ minutes, moderate 3 ounces of water/sports drink mixture (see details above) every 15 minutes Workout bar, chews, or gel containing 40 g per hour of easily digested carbs
180+ minutes, vigorous 5 ounces of water/sports drink mixture (see details above) every 15 minutes Workout bar, chews, or gel containing 50 g per hour of easily digested carbs