Marathon Training Weight Gain: How can that be possible?!

When you consider all the benefits of exercise, weight-control or weight-loss often top the list. Even as we find better whys for our exercise such as happiness, reaching a goal, overall health, or becoming stronger…weight is still a big factor in why people exercise. People who sign up for marathons have many different reasons for doing so. Losing weight might be one of them. Gaining weight during marathon training, on the other hand, isn’t what runners are generally setting out to do! It sounds counter intuitive, but it happens way more than you’d think. It’s a little mind blowing when you consider the number of calories someone must be burning with all those high-mileage weeks. Positive or negative, there has to be a good reason for marathon training weight gain.

Why do marathon runners gain weight? Despite intense exercise over the course of several months, weight gain can happen during marathon training. Sometimes runners overeat, convincing themselves they can eat whatever they want since they ran so many miles and burned a large number of calories. Other causes can include improper sleep or strengthened muscles.

You certainly don’t want to pack on extra pounds you don’t need before your race, but it’s also important to remember that gaining weight isn’t always a bad thing.

Unnecessary Marathon Training Weight Gain

I think we can all agree that society puts way too much emphasis on weight. Yes, we need to maintain a healthy weight and that’s important for living a long life. But having your entire day ruined because you see the tip of the scale by a pound or two isn’t positive. It’s much more productive to pay attention to how we feel. And quite honestly, as a runner, you can tell if weight gain is affecting your performance without stepping on the scale. So instead of worrying about a pound here or there, we’ll focus on why overall weight gain can occur while training for a marathon and how you can keep it in the range of allowing you to perform your best.


In my recent article, The Carbo-Load: Why do Marathon Runners Do This?, I discussed the importance of carbohydrates for a successful training cycle and marathon. Loading up on carbohydrates is something necessary for marathon runners to maintain energy throughout their training by building up glycogen stores. But there is a maximum of glycogen your body can hold, approximately 2,000 Calories worth between your muscles and liver. So if you continue to eat carbs beyond this or don’t burn it off…well, you can guess what happens.

When carbo-loading is used improperly this leads to unwanted weight gain in the form of excess calories. Although you will need carbohydrates throughout your training, you don’t actually need to “carbo-load” until closer to race day when the percentage comes close to 75% of your calories. Otherwise, you should be balancing your macronutrients between carbs, protein, and fat.

And when you’re training for a marathon, you’re suddenly going to feel like you need all those macronutrients, all the time. Think of it this way. The average runner is burning approximately 100 calories per mile, so if your long run is 15 miles, you (give or take) left 1,500 calories behind. That’s a lot! And you will undoubtedly be hungry. Like want to dive face first into a pile of pancakes, hungry.

But don’t forget to consider calories consumed during your run in the form of gels, etc. or any extra calories you may have eaten prior to your run to fuel.The hunger is real but it doesn’t mean you have 1,500 Calories to make up post run.

The biggest mistake runners make when it comes to fueling their training is that they think can eat anything they want. I wish this was the case, too (hello pizza, donuts, bagels…) and it’s hard to say no to those delicious things when you feel like you earned it.

Eating beyond your Caloric needs is usually the main reason marathon runners gain weight, especially if it’s more than a few pounds. If you’re in this boat, we’ll discuss later how you can get your weight back on track by fueling properly while still enjoying delicious foods.


Marathon runners are notorious for not drinking enough water and not replacing sweat with electrolytes. It can be hard to get right especially when the length of your runs aren’t always the same and you’re new to marathon training. Dehydration isn’t always severe, so sometimes you may not notice that your body is craving more fluid.

Instead, this can be mistaken for hunger, causing you to eat beyond what your body actually needs.

The other side of this is not hydrating enough during your long runs and downing sports drinks after your runs…although the electrolyte replacement is good, the excess Calories are not. This is not to say you shouldn’t be consuming any of these drinks, it’s just important to be mindful of what your body needs.

Poor sleep

Marathon training is extremely time-consuming. Most people are adding it into an already busy day, so one thing that often suffers is sleep.

As someone who gets up 5 days a week to work at 5 am, when I was marathon training last summer, I was getting up close to this same time on the other 2 days to do my outdoor runs. There was rarely a day in a 5-month time frame that I was sleeping in. I wish I could tell you that I was crawling into bed at 9 pm every night like I should’ve been, but I wasn’t. Pretty much never. Let me tell you, this wears on you fast. Especially when you’re logging 30-60 miles per week on top of the sleep deprivation.

Lack of sleep leads to stress in the form of increased cortisol levels. According to this article from WebMD, this cortisol imbalance can lead to a feeling of hunger even when a person doesn’t need to eat. They also state that the lack of sleep can reduce the body’s ability to metabolize carbohydrates. If you combine this with all those extra bagels you’ve been eating to fuel your long runs, the pounds are going to seem to practically appear out of nowhere.

“If you’re sleep deprived, your hedonic drive for certain foods gets stronger, and your ability to resist them may be impaired. So you are more likely to eat it.” -National Institutes of Health

Read more about the importance of sleep in marathon training in my article, “How Sleep Can Give You the Edge You Need in Marathon Training.”

Healthy Weight Gain in Marathon Training

If you’re someone who is seeing an extra couple of pounds on the scale when you’re pretty sure you’ve been doing everything else right, the gains during marathon training could be positive. It’s important to not get caught up in a number if you’re feeling good and performing well in your runs. It just might be that you’re actually getting stronger!

Building Muscle

Muscle weighs more than fat. Bet you’ve never heard that one before -ha. Yes, it’s a cliche that people like to use – but it is true if you’re replacing the fat in your body with muscle.

Marathon running is centered around cardiovascular endurance, but you are building muscle, too. This is especially true if running isn’t something that you’ve been doing a lot of previously. Running can build your quads, hamstrings, glutes, calves, and core. Weight gain will not be significant, but muscle mass does increase from running. If you’re a few pounds heavier, but your clothes feel looser, this is most likely what’s happening. And good for you! This means you’re becoming a stronger runner and probably getting faster, too.

Building muscle will cause weight gain when marathon training.

Necessary Fuel for the Marathon Distance

It is very possible for someone to start out under a weight necessary to withstand the demands that marathon training brings. For some, the extra Calories consumed may be necessary to perform their best as an athlete. If you have assessed your Calorie consumption and you continue to feel like your body continues to demand more nutrients and fuel, you probably need it. In this instance, weight gain is healthy and necessary. You’ll be keeping the extra Calories you need while building muscle. Your performance will reap the benefits.

Weight Management for Marathon Training

Don’t go into marathon training being concerned that you might gain weight. Many people lose weight and most don’t see much of a difference. However, if you start your marathon training and you notice that every week you seem to be packing on a pound or 2 there might be reason to believe that you’re not following through with your training in the healthiest way possible. Overall sluggishness is another big clue that your weight gain isn’t strength-related. By making these simple adjustments you can get back on track in your training long before your marathon arrives.

  1. Refuel Quickly Post-Run Your refueling window of opportunity is within 45 minutes of your workout. A good rule of thumb is getting a 4:1 ratio of carbs to protein. Here I discussed how chocolate milk is an excellent post long run drink. Getting in some electrolytes is also essential.  Not only will you be replenishing lost nutrients as well as repairing muscles, but you’ll also fill up with something healthy without feeling like you need to continuously eat all day long.
Whether you bring your own or not, water is important in a marathon.
Image Credit: from Pexels
  1. Stay Hydrated Since dehydration can lead to false hunger signals, be sure you drink enough water and supplement with electrolytes (sodium, etc.).
  2. Sleep You don’t want all of your hard work sabotaged by lack of sleep. Sleeping more will ensure that your body isn’t tricking your brain into thinking you need more food than you do.
  3. Maintain a Balanced Diet You can absolutely still enjoy a couple of pieces of pizza and a beer once a week to celebrate your hard work. But if this becomes an ongoing habit, or you are constantly convincing yourself you earned whatever food you might be salivating over at the moment, it’s time to rein it in. By paying attention to true hunger signals, having an overall sense of Calories you’ve taken in/burned (you don’t need to count) and not overdoing it on the carbs and sugar, there shouldn’t be any reason why you can’t maintain or even lose weight as you marathon train.

Remind yourself why you wanted to run a marathon in the first place. It most likely had something to do with finishing, running the whole distance, enjoying it with a friend, or getting a personal record. If you’re struggling to work properly toward your goal and you see that you’re gaining weight, then do something about it. If you’re feeling good and crushing your runs, there’s no reason to pay any attention to the scale.



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