Should You Eat Carbohydrates Before Exercise?

Learn whether you really need that plate of pasta before you exercise, and what kind of carbohydrates actually give your body a workout boost.

Ben Greenfield
5-minute read
Episode #78

Should You Eat Carbohydrates Before Exercise?

If you ask many physicians, sports nutritionists and dietitians, they’ll tell you that carbohydrates must comprise a major part of your daily dietary intake if you’re going to be able to maintain optimum physical performance. But is that really the case? In this episode, you’ll find out whether you really need to eat carbohydrates before you exercise, and if so, how much what kind of carbohydrates to eat.

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How the Body Burns Carbohydrates

The general consensus among nutrition professionals that active people need to eat carbohydrates before exercise is based on many studies that have been performed in the last 100 years, primarily linking muscle carbohydrate stores to a better ability to perform high intensity exercise. In addition, many doctors report that their patients who follow low carbohydrate diets frequently experience lightheadedness, weakness, fatigue and poor motivation – especially when they’re trying to exercise.

This makes pretty good sense, since when you ask your muscles to work hard or produce a very strong contraction, they need access to fast-burning energy – which is exactly what carbohydrates are. Compared to fats and proteins, carbohydrates offer a muscle pure sugar that it can use to produce energy, or ATP. Muscles (and the rest of your body) can still use fats and proteins to produce energy, usually by converting them into useable forms of sugars, fats or amino acids, but this process takes a longer time to complete and isn’t your bodies preferred form of making energy for high-intensity exercise.

What Happens Without Carbohydrates

So what happens if you’re completely carbohydrate depleted, and your body has no sugar to burn? First, you find it more difficult to produce an intense contraction, like a maximum bench press or an all-out sprint. Second, your motivation to exercise begins to drop, since carbohydrates boost tryptophan levels. Tryptophan assists with serotonin synthesis, and serotonin synthesis improves you mood and motivation. As a matter of fact, researchers from Arizona State University found that a very low carbohydrate diet significantly enhanced fatigue and reduced the desire to exercise in overweight adults.

But there are three problems with most studies that show carbohydrates to be important for quality of exercise or motivation to exercise:

  1. they don’t allow the subjects in the studies ample time to adapt to a low carbohydrate diet, which can take several weeks or even months

  2. they do not take into account ensuring that the mineral and nutrient intake of a low carbohydrate group is as high as that of a high carbohydrate group

  3. they feed the low carbohydrate subjects a higher protein diet, which can increase production of acidic compounds that could actually harm exercise performance.

One researcher named Steven Phinney has studied small groups of bicycle racers performing at a brisk bicycling pace (22-24 mph) for several hours. Unlike most bike racers in low carbohydrate studies, these bicyclists were allowed ample time to adapt to a diet of about 15% protein and over 80% fat, with the only carbs coming from the small amount of carbohydrates naturally found in meat. These cyclists’ performance was not affected negatively by the presence of nearly zero carbohydrates in their diet – although their muscle carbohydrate stores were significantly reduced. This was primarily because their bodies had become accustomed to burning fats as a fuel during exercise.

When You Need Carbohydrates

It’s been a little while since my What Should You Eat Before and After Exercise article, and I’ve been seeing quite a bit of research since then that suggests it is not necessary in all cases to eat before and after a workout. So when do you need carbohydrates for exercise and how should you get them? Here are 4 quick and dirty tips:

1. Don’t Eat Carbohydrates Before Moderate Cardio Workouts

During long cardio workouts, your body is actually very efficient at using fats as a fuel, especially when your intensity is not high. To put things in perspective, a champion marathoner running the Boston marathon is running at an intensity that would necessitate frequent carbohydrate feedings during that long workout. But an easy 90-minute morning jog does not require carbohydrates. You can simply roll out of bed and start running (I personally do this quite frequently). The first couple of weeks will be somewhat unpleasant as you grow accustomed to relying on fats as a fuel, and for that reason you can wean yourself off of long workout carbohydrates by having something like a sports gel about halfway through, but ultimately you won’t really need the carb load.

2. Eat Carbohydrates Before Hard Cardio Workouts

During hard cardio workouts, your body’s sugar needs are elevated and the muscles rely more on fast-burning carbohydrates as a fuel. But it is important to understand that you really do need to be exercising at a high intensity. When I ran an exercise physiology lab in which we measured carbohydrate utilization during exercise, people were usually running up a very steep treadmill incline at about 85-90% intensity before their bodies were burning primarily carbohydrates as a fuel. If you’re simply getting a little muscle burn or exercising under an 8 on a 1-10 scale during exercise, you don’t need dietary carbohydrates during a cardio workout. If you are actually at that high intensity, then you’re probably working out too hard to eat, in which case you can simply consume an easily digesting carbohydrate before you begin your workout. Fruit, potatoes, sports drinks or energy bars would all do the trick, and are generally best consumed 30 minutes to 2 hours prior to your hard workout (the bigger meal, the longer the time you’ll want to allow for digestion).

3. Eat Carbohydrates Before or During Hard Weight Training Workouts

An easy or short weight training circuit at the gym doesn’t really need to be fueled by dietary carbohydrates, especially when you bear in mind that your body naturally carries about 1,500-2,000 calories of storage carbohydrates that it can burn through, and it usually takes 1-2 hours of weight training to deplete this. In contrast, this afternoon I’ll be headed to the gym to do the Most Difficult Workout Ever Created, which is 2 hours of brutal lifting, and I’ve just finished a meal of rice crackers, yogurt and honey to get me ready for it!

4. Eat Carbohydrates Before or During High Calorie-Burning Activities That Require Extreme Focus

Due to the tryptophan-serotonin connection, and also due to the fact that low blood sugars can potentially decrease focus and intensity, you shouldn’t venture fasted or only fed on fats and proteins if you’re about to embark on something like a high intensity 2-hour tennis match. While 18 rounds of golf or even a game of baseball can be fueled on fats and proteins, if you’re both trying to focus and simultaneously burn a high number of carbohydrates, you should eat 2 hours before the event, and then consume 100-300 calories of carbohydrates during the event (and during a long, grueling focused event like Ironman, I personally eat 350-450 calories of pure sugar from sports gels for up to 10 hours!).

Ultimately, carbohydrates have their time and their place, but if you find yourself constantly relying on carbs to get you through every workout, you’re probably not doing your body any favors when it comes to becoming more efficient at fat-burning.

If you have more questions about eating carbohydrates before exercise, or your own tips about how to stop weight gain from happening when you exercise, share them in Comments or on the Get-Fit Guy Facebook page!

Carb Food Sources image from Shutterstock

All content here is for informational purposes only. This content does not replace the professional judgment of your own health provider. Please consult a licensed health professional for all individual questions and issues.

About the Author

Ben Greenfield

Ben Greenfield received bachelor’s and master’s degrees from University of Idaho in sports science and exercise physiology; personal training and strength and conditioning certifications from the National Strength and Conditioning Association (NSCA); a sports nutrition certification from the International Society of Sports Nutrition (ISSN), an advanced bicycle fitting certification from Serotta. He has over 11 years’ experience in coaching professional, collegiate, and recreational athletes from all sports, and as helped hundreds of clients achieve weight loss and fitness success.