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You may have been expecting to shed a few pounds when you ramped up your mileage in preparation for a marathon. It makes perfect sense considering that a 15-mile run would burn about 1,500 calories in a 150-pound person, not to mention your shorter maintenance runs during the week, all of which add up to some serious calorie-burning potential. Not so for me, though. As I'm entering Week 7 of my training, I've put on a good five pounds and the same thing happened the last time I trained for a marathon.

I talked to some fellow runners-in-training only to find they were also lamenting their growing waistlines. Between energy gels, carb-heavy recovery meals and all those sports drinks, I'm sure I'm consuming some (okay lots of) extra calories, but how's a runner supposed to properly fuel up without overdoing it?

I spoke to expert Nancy Clark, sports nutritionist and author of "Nancy Clark's Food Guide for Marathoners," hoping she could shed some light on the error of my ways. "What tends to happen is that you go for a 17-mile run and then you come home and eat pancakes, lie around and read the paper," she says, describing my previous Saturday eerily well. "You may not have burned off more calories than if you had run less and been more active the rest of the day," she adds. Her post-run strategy? "Re-fuel with a meal of protein and carbs and then ease up on calories the rest of the day," she says.

I vowed to cut out the pancake-fests, but surely a weekly overindulgence can't amount to a huge gain. That's when she explained some of the other things I'm doing wrong, like drinking sports drinks after my run. "Sports drinks should be consumed during exercise when your body needs the quick energy and the calories, not after," she says. Another mistake is thinking of my dinner as helping me fuel up for runs the following morning. "That's what breakfast is for," Clark says. I don't eat more than a little energy bar pre-run and fill up later. Wrong again. "I always tell my clients fuel by day and diet by night," she says.

Here's a breakdown of your daily calorie intake according to Clark:

• You'll need about 300 to 500 calories for breakfast before the run. Think granola bar, English muffin or whatever you can tolerate before activity.
• You need another 200 or so calories for every hour of exercise, depending on your size. This is where sports drinks and energy gels factor in. Though Clark says "real food" is a good alternative to engineered foods which are essentially "sugar by another name." She offers dried pineapple, Starburst, Twizzlers and hard candies as alternatives.
• You should re-fuel after your run with a mix of protein and carbs. She suggests chocolate milk as a good post-run drink.
• Lunch should be hearty. She also recommends a second lunch, which is essentially a more substantial snack.
• Cut back on calories the rest of the evening.

For those of you who've put on some weight, you don't have to carry it around until after the marathon is over. Clark admits it's difficult to lose weight when you exercise a lot because if you cut back too much, you'll sacrifice energy. She suggests a gentle strategy of "chipping away at the end of your day." Look for ways to cut 100 calories here and there and then keep it light at the end of the day. That might not sound like much of a diet, but if you follow her other suggestions and make a modest decrease in calories, that will add up to a significant loss of several pounds or more over the year. Plus, you'll start the race at your fighting weight.