While it would be a shame if the sole aim of cycling became to lose weight, it’s often a useful by-product of time on the bike for many. At the same time, if your doctor has mandated that a little off the middle might be good for your general wellbeing, cycling for weight loss can be very effective.
However, can you translate your weight loss target into a total in kilometres? The short answer is: sort of… To get to the bottom of the complex science and attempt to answer the question, ‘How far do you need to ride to lose 1kg of fat?’, we assembled a panel of experts.
Grab a calculator and find out what they advise.
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Breaking it down
Cycling takes effort, and effort requires energy, and burning energy helps us lose flab – we all know that. But beyond those generalisations, it would be useful to know precisely how much weight we can lose by cycling. So here’s the question: how far would the average rider have to ride to lose a kilogram of fat, assuming other factors such as diet and regular activities remain the same?
Science has the answer, but getting to it isn’t as easy as you might think – and always remember to consider your nutrition, because you can’t outride your fork.
‘Weight loss is not an exact science, and there are all sorts of variables,’ says Adam Carey, CEO of corperformance.co.uk. ‘But as a rough guide, a cyclist can calculate his or her energy expenditure this way: average watts × time in hours × 3.6.
‘So if you average 100 watts for two hours you burn 720 calories. Similarly, you can jump on a turbo trainer and do one hour at 200 watts, for example, which will also give you a calorie burn of 720 – or you can do it on your regular route if you have a power meter.’
Now it seems all we have to do is to calculate the total calories we need to burn to get to dispense with that 1kg of fat.
‘We can estimate that 1g of fat contains nine calories of energy,’ says Greg Whyte, professor of applied sport and exercise science at Liverpool John Moores University.
‘Assuming that’s all correct – which is a stretch of the imagination because everyone is different – it means 1kg of human fat tissue is the equivalent of 7,800 calories [870g of lipids × 9 calories of fat per gram].’
Let’s say you’re going to ride at an average of 200 watts. ‘Few of us are regularly going to average over 200 watts on a long ride,’ says Carey.
If you divide 7,800 calories that make up 1kg of body fat by the 720 calories you’ll burn riding at 200 watts for one hour, it will take you 10.83 hours – 10 hours, 49 minutes, 48 seconds to be precise – to burn 1kg of fat. Now let’s assume that on a flat course at 200 watts with no headwind you can average 30km/h. That means to burn 1kg of fat you’ll have to ride 324.9km. Easy-peasy. Off you go. But wait.
‘It’s not as simple as that,’ say Carey and Whyte virtually in unison.
Hunger pangs
‘There are some curveballs here,’ says Carey. ‘The first is your diet. These figures are based on the fact that you haven’t changed your calorie intake, and that you have a good, clean diet. The truth is we’re not very good at doing that, particularly because training stimulates appetite.
'If you sit two people in a room for half an hour they’ll be less hungry than two people who ride a bike for the same time. And if you treat yourself to a post-ride latte, that’s around 200 calories. That could negate half an hour of training if you’ve been averaging 100 watts.’
But that’s not all. ‘These figures assume you’re going to burn the best part of 8,000 calories of fat as your sole energy source, and that never happens,’ says Whyte.
‘Energy metabolism uses all available resources – we just shift our reliance from one source to another.
'I recently completed the Marathon des Sables [the epic desert running race], and on a long day I probably burned 8,000 calories, but I didn’t lose 1kg. The sums are compounded by carbohydrates and protein and it’s very complex.’
What type of riding you do will affect the ratio of fat to carbohydrate you burn. ‘From low-intensity riding through to your anaerobic threshold [maximum sustainable effort], you produce a respiratory exchange ratio [RER],’ says Whyte.
‘This compares the oxygen consumed to the carbon dioxide produced, and from that we can estimate what fuel is used. An RER of 1.0 or above means you’re predominantly metabolising carbohydrate,’ he adds.
‘An RER of 0.7 is pure fat, and you will only get anywhere near that figure at rest or by doing very light exercise. The harder you go, the greater the contribution from carbs. That’s why slow, steady exercise is known as “the fat-burning zone”. But you also have to be careful because any excess consumption of carbohydrate results in lipogenesis whereby, during the process of breaking down carbs, sugars are laid down as fat.
'These will be used as a fuel source if you exercise hard enough, but if you don’t they’ll be stored as fat.’
Now it’s starting to look as if we’re better off cutting out carbs and not cycling at all – or certainly not at maximum effort. But wait. There is another way.
‘If you do intervals, you can still calculate your average power output, but it has an effect on your metabolism after you’ve stopped riding,’ Carey says.
‘The advantage of intervals – short bursts of hard riding mixed with recovery periods – is that they increase your metabolic rate for the following 24 hours. The problem is they’re quite disruptive.
'They damage muscle fibres more than steady-state training and the damage lasts for up to 48 hours, so if you try to ride the next day you’re not as strong. Your power output might actually fall if you’re not trained to do it.’
Fast thinking
So there has to be a balance, and there’s another way of optimising fat burning on the days when you’re not doing intervals.
‘You can restrict calories on a long, slow ride and ride in a fasted state. Don’t eat before or during the ride,’ says Whyte. ‘This increases fat utilisation, but you have to ride for four to six hours. You can’t do it for an hour like you can if you’re running.
'Combine that with intervals to raise your BMR [basal metabolic rate], but don’t do intervals in a fasted state. That’s because you’ll be burning more carbohydrate so you need the fuel, or you may find you can’t complete the session.
'Worse, if you run low on carbs your body will enter a catabolic state and start breaking down muscle, because when you’re in “negative calorie balance” your body can’t utilise all of its fat stores.’
In short, you need to mix long rides on an empty stomach with well-fuelled intervals – ‘twice a week is ideal,’ says Carey – to optimise your fat-burning capabilities.
So where does that leave us? ‘How much fat you burn is wholly individual,’ says Whyte. However, if you get used to training in a fasted state your percentage of energy expenditure from fat could be anything from 20%-50%.
Using that lower estimate as our baseline, let’s return to that figure of 324.9km. If 20% of your total energy expenditure at that distance comes from fat, you’ll need to ride five times as far to burn off a kilo of fat.
‘In the real world, it’s not a perfect science,’ says Carey. We’ll give it a go, though. See you in 1,624.5km.
