5 running, diet and weight loss myths

5 running, diet and weight loss myths 

By Alister Gardner, Runner & Co-owner of xact nutrition 

We all run for our own different reasons, but for many of us, one of the top reasons is to burn a few calories and stay in shape! Rightly so, according to Harvard Medical School, running is one of the top activities when it comes to calories burned per hour. 

However, while running can play a big part in weight management and is also beneficial to our cardiovascular system and wellbeing, (1) weight loss itself is a little more complicated. It is about achieving the right balance between energy in and energy out, and that does not mean just exercise!

It doesnt help that there seems to be 101 miraculous diets out there, each touting failsafe results with sports stars and celebs to prove it (most of whom were in great shape to begin with!) The problem is often that following a particular type of diet means restricting certain food types.  When we start out we are motivated to follow the diet to the letter, and so avoid every single one of those badfoods.  This limits our options, which then indirectly leads to weight loss through calorie deficit. However, as time goes by, these diets can be hard to follow, so we begin to go back to adding the occasional forbiddenfood, slowly returning to our old habits.  

As for the myths of running, diet and weight loss, many have been circulating so long it would be easy to believe that there is truth in them.  Here are our favourite five:

Myth #1: By starting running I will lose weight

Regular cardio exercise has proved to lead to moderate weight loss in obese and overweight people (2), but the amount is not significant and would be proportionately less for those looking to shed just a few pounds.  Adding exercise to your routine is a part of good weight management, but just because you run this does not mean you will lose weight.  While running will improve your cardio, if, afterwards, you treat yourself to a slice of cake and a latte with whipped cream, it is going to tip the scales in the wrong direction.  We have to change our dietary habits too.  We also have to consider our overall effort throughout the day; if we are sedentary for the rest of the day then we will burn very few calories outside of that 10 km run.  On the other hand, others who do a slightly shorter run, may do garden work the rest of the day or take the family for a hike and so burn more calories overall.  The daily total is the important number.

Myth #2: The fat burning zone

We see it on the posters in the gym and it sounds logical: low-to-moderate intensity exercise burns a higher percentage of fat while higher intensity exercise relies more on carbohydrates.  So lower intensity should burn more fat right? Wrong. We need to think about the overall expenditure of energy in the form of effort x time rather than fat versus carbohydrates (glycogen).  An easy jog or brisk walk for 60 minutes may burn around 300 calories per hour, but an interval training session could achieve the same in half the time, meaning more time to work out and burn more calories. Just keep in mind that HIIT has a higher toll on the body and so is best limited to twice a week when starting out.

Myth #3: Use this workout to target belly fat”

You can also swap the word workoutfor diet, superfood or magical fat-melting cream.  This is really where it comes to click bait and gimmickry as the stomach is the most common place where we see fat accumulated. However, we do not burn fat with the muscles that are closest to it.  Our body fat is more like one big gas tank and it provides energy to the whole body.  So rather than dedicating our gym time to crunches, we are better off going for an all over body workout, strengthening our core, stabilisers and posterior chain.  This will also help us reduce the risk of running-related injuries too!

Myth #4: Weight-lifting will put on weight, not help me lose weight

If you were to spend many hours of your training time dedicated to the weight section of the gym then this might be true (however, the weight is likely to be in the form of muscle, not fat, and so your waistline should improve). Nevertheless incorporating some resistance exercise alongside your running will simply strengthen muscles with very little bulking up, and combining the two has proven to best help weight loss as opposed to doing one type of exercise or the other (3). Developing muscle endurance will also help reduce the risk of injury (as mentioned above), especially around the core and glutes.

Myth #5: Running on an empty stomach will burn more fat

Technically this has some truth but requires the right conditions and does not guarantee weight loss.  A pre-breakfast run means we will be running with lower glycogen reserves and therefore may require more fat to get us through the workout, but our bodies still have some reserves that will get used, so we either have to run for longer or go to bed with glycogen reserves already depleted.  However, as before, if we overcompensate by eating too much throughout the day afterwards we are not creating a calorie deficit.

As you may have noticed, there is a pattern in how these myths are debunked: if our goal is to lose weight then we must create a calorie deficit and just running alone might not do that. The best way to do this is by creating healthy eating habits and combining them with exercise.

Energy inis everything we eat. Processed foods tend to have added sugar and added fat to make them taste nice but that bumps up the total number of calories. Also, portion sizes, as recommended on the box, are not always followed and may seem small compared to what we are used to — I could easily get through three portions of pasta after a long run but that may mean way more calories than I need! But if we aim for healthy choices and cook from scratch, for example: carrots and home-made hummus instead of nachos and cheese sauce, then we can eat both well and healthily and also keep our calorie intake down.

Energy outis all the energy we burn in the day. It is made up of:

  • the exercise we do – exercise activity (very modifiable)
  • how we spend the rest of our day — non-exercise activity thermogenesis aka NEAT (modifiable), 
  • our basal metabolic rate (heartbeat, organs functioning, hormones etc), not modifiable
  • and thermic effect of food (digesting food), slightly modifiable.  

Elite athletes train twice a day and aim to do the very minimum between training to conserve energy. For the rest of us, if we want to create that deficit, we may have to look at how we spend our day as a whole, not just the 30 minutes on the treadmill. If we are stuck at the office all day then maybe a walk at lunch time could help burn an extra few calories, or we could commute by bike, which adds a whole green factor too! The more we do, the more it adds up. 

With all this in mind, we also need to think about our energy needs to complete a long run such as a half-marathon or marathon (as well as all the training to build up to these distances). During medium to high intensity exercise, our muscles will require a certain flow of energy to sustain the effort and this typically comes from our glycogen reserves. These reserves can usually sustain us for 60 to 90 minutes but afterwards it begins to feel like our bodies are going to crash and this is where energy gels and chews like the FRUIT2 and FRUIT3 come in. They are simple carbs to help fuel muscles during exercise. Gels and chews can still be used even if our primary goal is to lose weight, it is simply about the timing (during effort) of when we use them alongside a healthy, well balanced diet.

In summary, weight management has two sides to the coin, what we eat and how much energy we burn, and for many of us we need to take care of both.  Dont aim for rapid success with the latest diet trend (research shows that people will regain about half the weight lost(4)), but instead build in good habits.  Running is just one of them, and as runners, everything we do and eat is a part of working towards our goals!


  1. Effects of Physical Exercise on Cognitive Functioning and Wellbeing: Biological and Psychological Benefits 2018
  2. Isolated Aerobic Exercise and Weight Loss: A Systematic Review and Meta-Analysis of Randomized Controlled Trials, 2011 
  3. Aerobic or Resistance Exercise, or Both, in Dieting Obese Older Adults 2017
  4. Weight-loss outcomes: a systematic review and meta-analysis of weight-loss clinical trials with a minimum 1-year follow-up. 2007