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Cycling & weight loss – Part One

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John Phelan is back with a two-part blog on demystifying cycling and weight loss.  In the first part, he explains how our bodies burn fat, part two will reveal how we can achieve this whilst cycling!

“Why are there so many cyclists struggling to lose weight? I hope to shed some scientific light on the reason for this, and by doing so give you the best chance of achieving your weight loss goals using cycling as the main exercise.

To understand weight loss, it’s important to understand weight gain.  Gaining weight happens so slowly that most of us are caught unawares.  This is because it results from a positive calorie balance over time.  The time segment here, in this case, is usually a number of years.  For example, if you consume more calories than you spend on average for every given week, then you can very easily see how this would amount to a lot of excess calories at the end of the year.  Excess calories are stored for a rainy day, typically around the mid-section for fellas and around the hips for females. Our bodies use calories as fuel to move.  We can break down fat and turn it into calories, but we can also break down carbohydrates to do the same.  It’s not really important for this story to know that the actual energy being used by the body to move is called ATP, so let’s stick with calories for now.  We typically use both fuel sources (fat and carbohydrate) simultaneously to provide energy for movement, BUT, if everything is working well, we should predominantly be using fat for low-moderate intensity activities and predominantly use carbohydrate for moderate-high intensity stuff.

We are born with a glorious ability to store calories! We store carbohydrates as glycogen.  This store is limited to 500 grams.  We also store calories as fat. There are no limits to our fat stores. If you’re cycling at a high intensity, then your body should be predominantly burning glycogen as the fuel source.  The reason for this is the fact that glycogen can be broken down quickly by the body, and since you are pedaling along at a rate of knots, this means energy is needed quickly to fuel you.  Fat would take longer to break down and so you would need to slow down in order to use this as a fuel source.  This concept explains the “bonk”.  Bonking happens when a cyclist forgets to eat carbohydrates but keeps going at the same intensity.  The body runs out of its 500 grams of stored glycogen and then has no choice but to switch over to fat, slowing the rider down in the process.

On the other hand, when you are cycling along at a nice easy pace, fat should be the predominant fuel.  However, this is not always the case and this I feel is where many cyclists are going wrong. If you eat excessive carbohydrates in your diet and are simply not moving enough, your body will choose carbs as its preferred fuel for cycling, even at low intensity.  Why? Because carbs are much easier to convert into energy, i.e. your body goes for the easy option!  Watch out because this applies to all movements by your body throughout the day, not just for cycling.  The situation is not helped by the fact that many cyclists on a leisurely jaunt will fuel themselves with gels and/or stop off for coffee and scones.  By swallowing simple carbs, they are missing out on a lovely opportunity to allow their body to burn their fat stores when cycling.

We need to eat depending on our needs.  If our day contains little to no moderate-to-intense activity, then we simply do not require lots of carbohydrates in the diet for that day.  The diet for such a day should mostly consist of healthy fats, vegetables, and protein.  If your day involves an easy-paced cycle and not much else, then it should look exactly like the above day, i.e. less carbohydrate and more fat/protein. Let us say it is a Sunday and you plan on doing a tough spin on the bike after breakfast, then your breakfast should contain lots of healthy carbohydrates to fuel the intense cycle, and you should replace the glycogen stores with more carbohydrates during lunch after your cycle.

I hope that I was able to help you make sense of it all with the above blog.  There is more to it, but we will save it for part two.  In part two, we will look at ways to help you burn fat more efficiently and also at how technology, in the form of metabolic gas analysis, can reveal what proportion of your daily calorie expenditure comes from fat and what proportion comes from carbohydrates.  This is a very important ratio to be aware of when prescribing nutrition and exercise advice in the area of weight loss.”

John Phelan runs a clinic in Cork by the name of Life Fit Physio.  He also goes under the alias of The BikeFit Physio, specialising in physio-led bike fitting. 

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