Fueling for Exercise - Mercy Medical Center

Fueling for Exercise

Posted on: November 9, 2011

When and what to eat Whether you are new to running or a seasoned marathon runner, what you eat and when you eat can affect your performance and the way you feel during exercise.

It is all about timing

  Eating a large meal before you exercise may make you feel sluggish and cause cramping, an upset stomach, or even diarrhea. This happens because your muscles and your digestive system are competing with each other for your body's resources.

Your body can digest food while you're active, but not as well as it does when you're doing limited activity. Exercising muscles require a healthy supply of oxygen from the blood. The digestion process has similar needs: Therefore, you have a competition going on within your body, because your blood is trying to do two jobs at once.

Normally after eating, your blood goes to the stomach muscle to help it do its part in digestion. When you start exercising, some blood gets taken away from your stomach. Both jobs get done, but not as effectively, or as side effect free, as you'd like.

Does this mean not to eat before you exercise? No. Not eating before you exercise can hinder your exercise almost as eating too much. Low blood sugar levels can make you feel sluggish, heavy footed, faint, or tired. Your mental abilities may be affected as well, making reaction times slower.

So how do you find a balance? Everybody's different, but here are some general rules for timing your eating and exercise:

Breakfast, the fuel for champions

Never skip breakfast. If you are an early morning runner, grab a glass of juice, a banana or a slice of toast just to kick start your engine. Most of the energy you received from dinner last night is used up by morning, so your blood is usually a little low. This is normal and you may be fine, but if your evening meal was light on carbohydrates, you risk feeling sluggish or lightheaded while exercising. If you have an hour before your run or upon your return, make sure you have a balanced breakfast with a good source of carbohydrate and protein, and of course, a non-caffeinated fluid to rehydrate your body.

Time your meals and snacks

Allow at least 3 to 4 hours before exercising if you are eating a large meal. Smaller meals usually can be digested in 1 to 2 hours making it comfortable to exercise. A small snack, low in fat, can usually be eaten shortly before exercise.

Some things to keep in mind when timing your meals and snacks: Carbohydrates take about 1 to 2 hours to digest depending on the complexity or fiber content. Protein takes about 3 to 4 hours to digest. Fat requires about 5 to 6 hours to digest. This should help when planning your exercise routine. You may need to experiment a little during training, but never on a race day.

Eat smart after your workout.

A cold beer or some cheesy nachos may taste great after a long run, but to help your muscles recover and to replace their fuel stores, eat a meal that contains both protein and carbohydrates within 2 hours of your exercise session, if possible. A general rule is try to replace carbohydrate and protein (4 to 1 ratio) in a beverage as soon after a long run as possible, then follow up with a balanced meal. Watch the fat content because that will slow how quickly glycogen (muscle carbohydrate) can be replenished.


For more information contact

: Kathy G. Wise RD LD CWC, CWP Director, Healthy & Wellness, Mercy Medical Center 1320 Mercy Drive NW, Canton, OH 44708 | 330-489-1479 Kathy.wise@cantonmercy.org

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