How Training For a Marathon Affects Your Weight

Training for a marathon can be a grueling affair! You can get in shape for a 5K or 10K in a few weeks, but it takes months of hard work to get in shape for a marathon. You watch your diet, work out daily, and push yourself as hard as you can just so you can keep running and reach that goal!

But it can be highly discouraging to feel like you’ve gained weight after all that effort. Well, before you throw your efforts out the window, here is what you need to know:

1.     You’ve packed on a lot of muscle

As you trained for your marathon, you developed a lot of muscle–particularly in your legs. Your body has felt the increased demand for energy, and this it has responded by increasing leg muscle to store more energy. Muscle weighs a lot more than fat, so the reason you may feel like you’ve gained weight is due to the fact that you HAVE. The good news is that it is all lean body weight, and it is very healthy. It’s just a bit heavier, but not something to worry about!

2.      You’re storing more energy

Every time you run a marathon, you burn around 2,500 calories. That’s more than the average person burns in an ENTIRE DAY! It should come as no surprise that your body needs to store more energy now that you’re working your way up to running a full marathon. But for every ounce of blood sugar (glycogen) your body stores, it also stores around 3 extra ounces of water. That water weight will show up on the scale, but it’s just your body’s way of coping with the increased demands that will be placed on it as you run the marathon.

3.     You may be over-eating

When you train for a marathon, you know that you need to eat A LOT of food in order to have the energy that will be used up in your race. But many people tend to over-estimate the amount of food they need to eat, and they end up eating too many calories. This can cause you to slowly gain weight.

This may sound silly. After all, you’re running for hours every day, right? Well, the truth is that weight loss is simple mathematics. As long as the calories you are burning exceed the calories you are eating, you will continue to lose weight. If you eat more calories than you burn, you will end up packing on the pounds.

Take a look at your diet and see if you’re eating the proper number of calories for your body type and your daily activity. If you’re not running for hours on end, you don’t need to eat as many calories. Of course, the diet of a marathon runner is much different than the diet of a regular runner, so it’s important that you know how you should be eating. Don’t just add a lot of calories to your diet, but make it a point to study up on the marathoner’s diet before you start training.


The truth is that MOST marathon runners gain weight in the weeks leading up to the run. It’s just par for the course, and it’s your body’s way of coping with the increased demands you are placing on it. Don’t worry about it, but keep training, dieting properly, and working hard. Make sure to get plenty of rest to give your body time to recover. When you finally do run that marathon and cross the finish line, it will all be worth it!


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