Why You Might Gain Weight While Training for the Marathon

Whether you are an elite runner or a first time marathoner, training for the 26.2 mile distance requires months of training and countless hours and miles recorded out on the roads. It only makes sense that this kind of demanding training regimen would result in significant weight loss for anybody crazy enough to take it up.

So why do some runners report actually gaining weight during marathon training? Is that even possible?

If you are one of those runners who is experiencing this anomaly, there may be a few explanations as to why this could be happening. In this article, we’ll outline three possible reasons you might gain while training for the marathon and hopefully help you understand that it may be a normal occurrence.

Gaining Muscle Mass

You body responds to exercise by making a number of adaptations and physiological changes. One such change is the formation of muscle mass.

Yes, even distance running can promote muscle growth, especially in the regions of the legs that are being used the most. Add into that any weight lifting and strengthening exercises you may do and BOOM -> muscle gain!

Muscle mass is denser than fat mass, meaning that one pound of muscle takes up less room on the body than one pound of fat. If your body looks the same or even trimmer, yet you are heavier on the scale, the addition of muscle mass could be to blame. And that is not a bad thing.

Storing More Glycogen

Untrained athletes who begin an endurance-training program can increase their body’s ability to store muscle glycogen by 60-70%. Endurance-trained athletes consuming a high carbohydrate diet and/or carbohydrate loading can also increase muscle glycogen stores by nearly double that of the untrained state.

As you may have read in the article on carbohydrate loading, for every ounce of glycogen, the body also stores 3 ounces of water. That extra water your body is storing will show up as extra “weight” on the scale. Water weight will contribute even more to overall weight if you are being more diligent at staying hydrated than you were before beginning your training regimen.

Water weight will fluctuate throughout the days and weeks and is not reflective actual weight gain as fat mass. Remind yourself that being able to store extra glycogen and fluids is a good thing- you will need this for training and especially race day.

Overestimating and Overeating Your Energy Needs

One common mistake that runners make, veteran or newbie, is overestimating their energy needs, or how much they need to eat in response to their training. It seems like logging 20 miles on the roads over the course of a few hours should give us a free pass to eat anything our hearts (or stomachs) desire. But it is easy to overestimate how much we actually need and worse, it is easy to make bad choices if we feel like we “earned” it.

The amount of calories we burn during a run is variable depending on the pace/intensity/duration of the run and size of the athlete, but in general we can expect to burn between 80-100 calories per mile. For convenience sake, let’s say I burn 80 calories per mile and just ran 20 miles. Here are two possible scenarios of what would happen next:

Hidden calories

1) I shower up and head out to the local bar for the 12pm Packer game. I am starving and feeling like I deserve a treat so I order a basket of boneless buffalo wings and fries. This could be anywhere from 800-1000 calories, depending on if I am in a sharing mood. Add in the ranch dipping sauce and we are talking another 200-300 calories. Now let’s add the 3-4 pints of beer (Miller Lite because I am “health conscious” and from Milwaukee): another 400-500 calories. Grand total? 1400-1800 calories

During my 20 miler I burned about 1600 calories. I easily made up this amount and more with food that didn’t offer much in terms of nutritional value. If I fueled myself during the run with gels or sports drinks, which may have been necessary, then my energy intake is higher still than what I burned.

Although it seems that I needed to replace the calories burned during my run, I overestimated how much that might actually be and how quickly the calories can add up, especially when not choosing the best foods.

Not eating soon enough after a run

2) Maybe the Packers play the late game so instead I go home, shower, and pass out on the coach for a few hours. When I wake up I am ravenous and looking for the quickest, easiest thing I can eat. Cereal looks good. Three bowls of Fruity Pebbles later and I am still hungry, but now with a taste for sugar. Onto that pint of ice cream I tried to hide in the back of the freezer. Once that is gone my stomach really starts to hurt and I begin to realize that this was not a good thing that just happened.

This is a bit of an exaggeration but the point is that sometimes we do not want to eat right after a run or we are so exhausted that we would just rather rest a bit. Unfortunately, our bodies want food and they want it now.

The longer we wait to replace what was lost, the more attractive the sweets and fatty foods become because our bodies just want to get fuel back as quickly as possible. Sugars are easily absorbed and fats supply the most energy, so naturally that is what we will crave if we let hunger get out of control.

All of your hard work towards weight loss can be negated by these momentary lapses of judgment that come from making food choices based on reward or uncontrollable hunger.

Final Notes

  • Weight gain during marathon training is more common than one might think. The important thing to think about is the reason(s) why you are gaining weight. Increased muscle mass and glycogen storage are good things. Overcompensating for your energy expenditure, however, is something you can fix to get back on track.
  • Remember that as you start training more, you might also be resting more. Marathon training takes a lot out of you and you may not be doing some of the same activities you used to: weekend hikes, mowing the lawn, cleaning out the attic, etc. If your daily life outside of running has become more sedentary, your body will require fewer calories for energy than before.
  • Finally, weight is merely a number on the scale and just one measure of overall health and fitness. Pay attention to how fit and toned you look and feel, how your clothes are fitting, and what your body fat percentage is (if that measurement is available to you). If you are good in those areas, then the weight gain is due to the other factors discussed and not a gain in fat mass.

Like What You've Read?

If so, start our FREE 4-part Marathon Nutrition Series where I'll walk you through how to prevent the dreaded marathon bonk and race faster at your next marathon.

Here are just some of the topics we will cover...
  • How to calculate your exact glycogen storage and carbohydrate use so you know exactly how much you have to refuel
  • How to calculate your sweat loss and re-hydration rate to maintain optimal performance.
  • How to develop your individualized fueling plan using you sweat rate and glycogen usage.
  • How to practice during training and fuel up for race day.
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References

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3 Responses on “Why You Might Gain Weight While Training for the Marathon

  1. Thank you for this article. As an avid exerciser and group fitness instructor I am used to being very lean and toned. I have maintained the same weight for a long time (5’6″ 106-107 pounds) and workout (admittedly) like a crazy girl! I am super interested in nutrition and cook all of my families meals from scratch and eat a GF diet and feel great. Then I started the long-run portion of training for my first marathon……….I have upped my calories a bit, upped my protein about 25%, and started really being good about my water (170oz/day) but have noticed a lovely 3-4 pound increase on the scale. Had my body fat tested and it was 10.1! Yikes! I have been wondering what I have been doing wrong and this article has been a great starting point to help me figure out how this change in training is affecting my body. BTW, I run about 40 mi/week and alternate with stair mill, xbike, bootcamp classes, weight lifting, interval training, bikram yoga, etc….

  2. ‘The average body fat percentage for U.S. females is around 32%, with the ideal at 22%. Athletic females should be around 15-20%. You could have an eating disorder if you are below 10%. Remember these are guidelines; your physician should help you determine the ideal weight and body fat for you.’

  3. Thank you for the article! The article helped me recall what my intuition was telling me. I’m trainning for my 19 marathon and I want to qualify for the Boston Marathon. I am 36 and I need to qualify at 3:10… Anyhow, I weigh 185 and I realizing more and more that if I want to fulfill my dream, I need to empower myself with the knowledge of the basic numbers (calories burned, carbs needed, etc)

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