Hard to Stomach

12 October 2005

Dear Chris,

Can I eat before I have a workout? Or do I have to wait an hour, like they say for swimming? If so, why?

John in Toronto

Dear John,

The short answer to your question is it depends on what you eat and how much.

Your body needs energy to carry on its basic functions and this is especially true when you exercise. Your body breaks down carbohydrate into the simple sugar glucose and uses some of it immediately (as blood glucose) and stores some of it for later (mainly as the complex sugar glycogen). When you exercise, your muscles use both glucose for immediate energy and glycogen for longer lasting energy.

Generally it takes 3-4 hours to digest a large meal, 2-3 for a small meal, and an hour for a snack so time your workout with the type of meal or vice versa. You'll want to have a quick source of energy for your workout so it's best to have a light snack which is high in carbohydrate and low in fat up to an hour before. Eating a large meal, especially one high in fat or protein, just before you workout will make you feel sluggish and may give you indigestion or nausea because during exercise, blood moves away from the digestive tract to the working muscles.

So much for pre-exercise eating. What about eating after you exercise?

Studies suggest that if you are a moderate exerciser and only work out a few times per week, you need not worry about having a post-exercise meal. Your body will have plenty of time to recover from the exercise since you are leaving a couple of days in between sessions. If you exercise intensely and daily, you should eat within an hour after exercising because you need to replace the muscle glycogen you will have depleted. In this case, you should consume both carbohydrate and protein.

And remember, whether you exercise a few times a week or every day, moderately or intensely, be sure to drink plenty of fluids.

Chris

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