Why You May Not Lose Weight Running a Marathon

Why You May Not Lose Weight Running

Many first time marathoners expect that the marathon training process will automatically lead to weight loss. It makes sense: Running 50+ miles a week, how can you NOT lose those last 10 pounds?

But for many runners, marathon training leads to the scale creeping up, not down. I fit squarely into this category: I’ve run 25 marathons and have never lost any significant amount of weight training for any of them.

But fear not! The scale may be deceiving you (or maybe it isn’t, but I’m getting ahead of myself).

Why You May Not Lose Weight Running

Increased Food Intake To Fuel Extra Mileage

No doubt about it, you burn a ton of calories doing a 20-mile run. But you need to fuel those 20 miles somehow.

When done responsibly, additional mileage means additional calories; before you run, during your run, and as you recover. You need to consume enough healthy calories to keep your body fueled and healthy.

The additional calories you burn on a run should be nearly balanced out by the additional calorie intake as fuel.

Water Retention

When you begin to run more, your body will begin to store additional water to repair your muscles. You also should be drinking more water to ensure you are well hydrated.

This water retention will add pounds to your scale. However, that number isn’t an accurate reflection of your ‘real’ weight.

Muscle v. Fat

While marathon training you are (hopefully) gaining muscles in your legs and core. Muscle weighs more than fat, so even if you are losing fat, an increase in muscle mass may balance out any loss of fat.

It is fairly common for runners to gain weight while marathon training due to this increase in muscle.

When The Scale May NOT Be Deceiving

There are some instances where you may actually be gaining weight (bad fat weight, not good muscle weight).

Post-Run Hunger

For many runners, doing so many miles leaves them feeling ravenously hungry. Especially after a long run, it’s common to come home and want to (and maybe do) eat everything in sight.

It’s easy for this post-run feast to get out of hand, either in food quantity or poor food quality.

Read MoreDont Do After A Long Run


Beware of the phenomenon of thinking you get a free pass on all foods because of all your running. It’s easy to rationalize less-than-nutritious foods after a run.

Personally, I have a habit of ‘rewarding’ myself with junk food after a run. ‘I did that long run, I can have this cupcake’ or ‘I’m training, I can have an extra serving.’

Do I need to say what a terrible habit this is?

Social Calories

While a post-run mimosa brunch or a quick stop by Starbucks with your running buddies is great for your social and emotional life, it can be not so great for your weight.

These post-run festivities can easily lead you to consume more calories than you burned on your run.

So What To Do?

The scale only measures one metric, and that number may not be very accurate or helpful, especially while marathon training.

So what to do if you still want to do some type of nutrition or weight tracking during marathon training?

Food Tracking

Food and nutrition during marathon training is a very important topic, and one I come back to often, but nutrition specifics are beyond the scope of this post.

Eat mindfully, track your food intake and watch your portion sizes.

Create a list of enjoyable things you can do to reward yourself that don’t involve food. I’m a big fan of celebrating every victory, but food isn’t the only way to do that.

Energy and Other Intangibles

Listen to your body. How do you feel? Do you feel like you have more energy? Do you feel stronger?

While these measures can’t be tracked by specific metrics, they do a much better job telling you how you are progressing than a number on a scale.


If you need to track something, track your body measurements instead of (or at least in addition to) your weight. Your measurements will do a more accurate job of showing you when you’ve lost fat and gained muscle than your weight will.

If you don’t want to track specific measurements, pay attention to how your clothes fit. My guess is you’ll notice a difference in fit (for the better) even if the scale doesn’t reflect it.

While doing my first few marathons, I went from a dress size of 14 to a 10, without losing a pound.

Body Composition

Many scales now have body composition capabilities built into them. While I doubt these measurements are terrible accurate when compared to true scientific body composition measures, they do provide a consistent measure. If you use the same scale regularly, while it may be off, it will be off in the same way, every time.

When using a body composition scale, be sure you use it under the same conditions every time. Same time of day, same clothing (or not), same food/water intake (or not) so the measurements will be as consistent as possible.

How Often To Track?

There is a great debate on if you should weigh yourself every day.

I weigh myself every day, first thing in the morning before I drink any water. By doing this, I get a better sense of my current weight range and how my weight regularly fluctuates. If, when I weigh myself in the morning, the scale says I’m up 3 pounds since yesterday, I understand that there is no way I gained 3 actual pounds in one day. It’s water weight or something similar.

But if you are the kind of person who is going to stress out over every ounce, every day weigh-ins are not going to be a good idea. Even if you eat and workout perfectly, the scale will occasionally go up. Weight and composition measures fluctuate greatly based on food consumption and hydration levels. The added stress of daily weigh-ins is not going to do you any good.

Get to know your body and how you emotionally respond to the scale and what it tells you.

If you find everyday weigh-ins informative like I do, go for it.

If your stress levels start to rise every time you go near the scale, stick to weekly of monthly weigh-ins.

Why You May Not Lose Weight Running


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