Do Runners Lose Weight After a Marathon?

The Set-Up

It may seem contradictory, but if you've prepared yourself properly, you'll actually go into your marathon a few pounds heavier than usual. This is because to store glycogen, your body's chief source of energy in a marathon, you need to store lots of water along with it -- about three grams for every gram of glycogen. You can store up to about 500 grams of glycogen in your liver and muscles, which means carrying as much as 1,500 grams of water you normally don't need. This necessary pre-marathon ballast translates to as much as four pounds of extra weight -- all of which you'll burn off in the course of your 26.2-mile trek around town.

During the Marathon

Depending on your pace, the weather, how well you've "carbo-loaded" before the race and how much you manage to drink along the way, you're likely to be down a few pounds from your starting weight when you cross the finish line. Curiously, the faster you are, the more weight you're apt to lose, possibly because speedier runners don't need to tank up during the race as much as those in the four- or five-hour crowd. Some runners lose as much as 5 percent of their body weight during their 26.2-mile jaunts, which could be anywhere from five to 10 pounds -- an amount that would signal a medical emergency in a lot of settings.

Immediately Post-Race

No matter how the marathon goes, you'll finish it in a state of near-total glycogen depletion. According to two-time Olympic marathoner and exercise physiologist Pete Pfitzinger, your body can most readily replenish its glycogen stores the first two hours post-race. Of course, you may not feel like doing anything other than lying in a heap for a few hours after you finish, meaning that it may take you several days of diligent carbohydrate consumption to boost your energy stores -- and thus your weight -- back into the normal range. Try to think of your post-marathon feeding as part of the race itself, so that you don't forget you have a job to do even once your finisher's medal is safely in hand.

Days and Weeks to Come

Training for and running a marathon is more than a physical challenge and a test of your mettle. It's also an emotional investment -- especially if you have a do-or-die goal such as running fast enough to qualify for the venerated Boston Marathon -- and a lot of runners suffer from what coach Rick Morris of RunningPlanet.com calls "the post-marathon blues." This may even be rooted in part in a marathon-induced deficiency in the neurotransmitter choline, which is found in abundance in eggs. Since depression is often linked with a decrease in appetite, if you find yourself in the throes of a persistent dark mood after your marathon, monitor your weight to make sure it doesn't drop unduly, and if necessary see your doctor.