It’s a well trodden path, even before the additional challenges presented by lockdowns and the virus, you decide you need need to lose some weight so you are going to become more active. And to do that you are going to take up running.

But wait… What is going on ?!?!?! You are weeks into being a “runner” and far from losing weight you are actually putting it on!?!?!? What the hell is happening, this isn’t what you signed up for at all… Trust me when I tell you that this is an incredibly common “side effect” of starting running, but (generally) is not permanent. Here’s why;

1) You are over compensating on the calories.

This is by far the most common reason and I could almost retitle this blog “The number 1 reason you will take up running AND put on weight initially”. You ran for 30minutes, but ate extra beforehand (you read somewhere that you have to “fuel your run”) and then after your run you have some cake with a coffee because “you earned it” (NO!! You didn’t…). And finally, because you are ramping up your activity level you will probably feel a little more hungry too… The net result is that you have increased your calorie expenditure by a very small amount, but increased your intake by a lot more. The maths just will not work. Gaining and losing weigh is not rocket science:

To lose weight you MUST be in a calorific deficit. End of story. If you have a calorific surplus then you WILL gain weight. Often, new runners hugely over estimate how many calories they might use whilst running. Therefore they end up over eating and gaining more weight.

2) Fluid Retention (you have swollen up).

Running, especially in the early days causes micro-tears in your “running” muscles. These tend to be quite large muscles (Quads, Glutes, Hamstrings…) therefore there is likely to be quite a lot of “micro tear” damage in aggregate. Don’t panic, this is not an injury! This is a good thing, because as your body repairs these minute tears it is also building a stronger muscle and adapting you to being able to run ‘better’. Over time, running will cause less micro-tears because you have adapted.

However this repair process will cause inflammation (again perfectly normal, no cause for concern, nothing to see here…). With inflammation comes increased blood flow to the affected muscles (looks red…) and you will also retain more fluid. Because we are talking about large muscles, and in the early days of running quite a lot of micro-tearing, the effect of fluid retention can be quite marked.

It will pass!! As your body gets over the initial stages of adaption to this new form of stress, you will have a greatly diminished inflammatory response to your runs. (Other than when you go really hard).

3) Your muscles are taking on more energy reserves.

Your muscles store glycogen. This is all linked to energy production and if that is something you are interested in then I have written much more here about energy systems. When you start running, you will deplete your muscles glycogen stores. Part of the “adoption response” is that your muscles will learn to store more glycogen than they did before. Effectively your muscles would be saying: “just in case he/she makes us do *that* again – we will be ready next time!”

As a bit of a double whammy for you, glycogen binds to water. Therefore you are not only storing more glycogen, but you are retaining more water. There is nothing you can do about this, other than to know that in time you will adapt, and this will be greatly reduced. Part of becoming fitter is about becoming more “efficient” – you will be able to do a lot more “work” for much less energy expenditure. Short term (months) this will lead you to weigh more than you “really” do.

4) Too much HIIT – you know that “fat burning” miracle some idiot promised you!

Whilst normally associated with our friends the “gym bunnies”, HIIT (which stands for High Intensity Interval Training) is also a “thing” for us runners. In the early days, when perhaps you are doing a walk / run session towards a first 5k, you are actually doing intervals! Later on, when a 5k run is trivial for you, you will be doing sprint intervals and hill repeats. Again you are doing “HIIT”.

High Intensity is relative to your stage of fitness. Therefore, particularly in the early days, many of your runs will represent “High Intensity”. Combine that with a quick recovery and then do it again and suddenly c25k is a HIIT session!

But wait Ed – all the PT’s tell us that HIIT sessions will “set out bodies alight and turn us into human fat burning machines…”. So what’s the story with HIIT being bad for you? It isn’t!! As a way of increasing your fitness, a HIIT protocol is HUGELY effective. But as a strategy for losing weight and “burning fat” – absolutely hopeless and very inefficient. You are training totally the wrong energy system to achieve meaningful fat burn.

But there is more bad news. All exercise causes stress. Bit like “cholestrol” we talk about good stress (which exercise is) and bad stress (bereavement, divorce, being fired) – but honestly your body is not that sophisticated. It just perceives more stress in aggregate.

Without delving into all the biology, in response to elevated stress levels your body will produce more Cortisol. That in turn can lead to insulin resistance, increased thyroid stimulating hormones, reduction in testosterone production in men and progesterone in woman. Again – DON’T PANIC!! You are not going to die… But if this continues for a prolonged period of time, or becomes a recurring pattern, then you do have a problem. Against this hormonal landscape your body is going to find it VERY difficult (read “it won’t”) lose weight.

So the take away here is – HIIT is good, when applied and used correctly. It will make you a more efficient runner. You should limit the amount of HIIT work you do and understand exactly what you are trying to achieve with it. Importantly if someone tries to sell you a “fat burning HIIT class to transform your body into a human furnace”… just politely tell them what to do with their Cortisol 😉

5) And rest!

In simple terms, “getting fit” is a repetitive process of overloading your body with training stress, and then letting it adapt (become stronger, leaner, more efficient) during periods of rest and then repeating. There is a little more to it than that (!!) but in a nutshell that is the game you are playing.

You become fitter during rest & recover not when you are actually exercising, puffing and panting. If you don’t get enough recover, you won’t get fitter. You will just get sweaty.

The temptation for many (at all levels of experience!) is to really push the HARD WORK training part, and skimp or completely overlook the recovery / adaption EASY WORK part. You see this in people that always go out and try and kill themselves so they will get more “gains” (they want to be a fat burning furnace). They don’t listen to their bodies telling them to back off (no pain no gain right) and eventually they have to stop because they injure themselves with torn muscles, tendon damage or worse (running is so inherently dangerous… nothing to do with dodgy training protocols).

From a weight gain perspective, long before they are laid up unable to do more than hobble, they will have put their body under huge “stress” (see point 4 as to why that is a problem) and caused an excess of tissue damage (see point 2 as to what happens then). Far from losing weight, they have created a perfect storm to ensure that they will almost certainly GAIN weight.

One of the big advantages of working with a Coach is to benefit from a training programme that MAKES YOU REST AND RECOVER, along with enough (good) stress to promote adaption. Yes, you probably will gain weight to start with, but honestly this will be temporary, for the reasons you now understand!

As you get fitter, a lot of changes will happen to your body. Running is a cardiovascular exercise, so you are improving the health of your heart, this has more benefits than you would immediately think. Running will promote improved muscle tone (NOT muscle growth!!!!) and you run with your whole body so you will tone all your muscles. Toned muscles “improve your shape” and most people are pretty happy with that one. Finally some “interesting” things happen to your appetite and mood, will write about that another time, but the outcome is you will eat less and not feel like you are “dieting” (because you won’t be!) and that dear reader is how your calorific deficit will be assisted by running.

6) You gained MUSCLE and that is heavier than fat

There is a good reason why I called this post “5 reasons” and that is because the myth that you will have gained muscle mass (to any meaningful extent!) is UTTER RUBBISH. It is in fact even more stupid a proposition than believing you are going to be a “fat burning furnace”.

  • Running is a cardio activity with highly repetitious body weight loading of your muscles. This promotes muscle toning not hypertrophy (muscle growth).
  • Building muscle takes A LOT of work, consistently, over a long time. (Ask any successful body builder). You are not going to accidentally “put on muscle mass” and your are CERTAINLY not going to do anything like that on a beginners running programme.
  • Bit like cycling, running is about power to weight ratio and cardio fitness. Therefore as you become a more experienced runner your programme will lead you to NOT gaining muscle mass (you will only have to carry it all up hill as extra weight), but rather to develop super efficient energy systems and toned muscle tissue (including tendons and ligaments) so you can perform a repetitive action at pace without injury for the minimum possible energy consumption. You will want to achieve your optimal “racing weight” – but that really is a WHOLE OTHER POST!

Net result : you will not have gained muscle regardless of what Karen in your Facebook runners group tells you.

Running offers many health benefits and in the long term “may” assist with weight loss. But if you want to lose weight running is NOT your best option. It will only help as part of a calorie controlled diet! DO NOT STARVE YOURSELF. Just eat slightly fewer calories than you use each day.


Ed Stivala is an England Athletic qualified Event Group Coach specialising in Endurance Events. His practice specialises in performance coaching for runners of all levels. He also holds qualifications in Personal Training, Nutrition and Swim Instruction. 
When not Coaching, he competes in Duathlon and plays golf very badly!

We love hearing from you.

Let's collaborate.