It has long been a source of amusement to my friends that I have maintained such a hefty bulk despite my veganism. It is true: I have taken being vegan as a sign that I shouldn’t deprive myself any further, and am guilty of gravitating towards the junk food end of the plant-based spectrum. I once ate four huge filled doughnuts in one sitting on the basis that vegans rarely get nice doughnuts, and “they were probably made of kale or something”.

A year ago, I decided something had to be done. My father died of a heart attack, and my body shape ticked all the boxes of someone headed the same way. There was another issue. My dissatisfaction with the way I look means I tend to wear one or two more layers of clothing than the season dictates. I can often be found at a bar sweating profusely, which, besides preferring the Crawley Pizza Express to the Woking branch, is another degree of separation I am proud to have from Prince Andrew.

I have had issues with my body all my life. I was a fat child and only lost weight during my A-levels, enjoying a three-year stint of being “skinny”. This generated a sense of euphoria similar to how Chesney Hawkes must have felt for the three years that followed the release The One And Only. I then piled it all back on at university. The girl I was seeing at the time found my weight gain fairly unappealing, leading to a campaign by her and her friends to “hint” me into losing it.

All this has left me with an ongoing hangup about my physique. I remember the first time I took my top off on television. When the show aired, somebody tweeted to complain that as a result of watching me she had been unable to finish her dinner. I assume she didn’t mean because she was so sexually aroused.

I bought a Wu-Tang Clan T-shirt so tight I feared it might lead to a cease-and-desist order

Last year, I decided to set myself a goal, one that involved a very simple metric: a Wu-Tang Clan T-shirt I had bought online from the US. When it arrived, I realised that it looked so ridiculous that wearing it might lead to a cease-and-desist order from the group for fear that my doughy body squeezed into their merch could damage the brand. I decided that my goal was to be able to wear that T-shirt in public without feeling ashamed. I was not even allowed to do the bigger-man trick of wearing it under an open shirt.

Facebook Twitter Pinterest ‘I have, of course, tried to lose weight many times, and succeeded – only to put it straight back on.’ Photograph: Pal Hansen/The Guardian

I have, of course, tried to lose weight many times, and succeeded – only to put it straight back on. I wanted this to be different, so I resolved to make changes that would be sustainable. I have done 1,200-calorie days and hit the gym hard, and you get results quickly; but I also quickly feel miserable (for me, usually around day two). I fall off the wagon badly, before eating the wagon in its entirety. This time I accepted that some of the things I was going to try would fail. I had to: based on the evidence of the past, everything would fail.

First I decided to get a personal trainer. Although expensive compared with going to the gym alone, it was necessary because my levels of self-discipline are pathetically low. For example: only six paragraphs into this article, I have stopped for an hour to watch the second half of Jurassic World on TV. When the film ended with a mosasaurus emerging from the water to chow down on the lab-created Indominus rex, it made want to have a large snack, which I went off and did. In the same way, when I go to the gym, I can often be found doing three reps of something before looking at my phone, messing with the settings on my headphones, and then trapping someone in conversation by a treadmill until they ask to be left alone.

A personal trainer forces you to use all the strange equipment that you would otherwise avoid. My local gym is filled with people I consider experts, who do those weird exercises that you see in Rocky montages, flailing ropes and standing on one leg while you throw a large sack at the ground repeatedly, before pushing a sled up and down the gym like a ’roided husky.

I couldn't tell David I was dying, which meant we often had to take a break because I had started crying

My own trainer, David, is an Adonis. He once posted a photograph on Facebook to show how badly he had let himself go over Christmas: it was such an incredible example of the human physique that I nearly saved it as my wallpaper. Rather than doing an exercise and then looking at my phone for 10 minutes, David had me exercising continually. We would move from one station to the next, me sweating even more than a fat man wearing too many layers of clothing in the summer. I also had the blessing or misfortune of not feeling comfortable enough with David to tell him I was dying, which meant that I would often be in the middle of a set and David would tell me to take a break because it’s not normal to be crying.

To avoid messing up a busy day, I had to do the sessions early in the morning, often meeting David at 6am. Any later would have meant not taking my kids to school, which I don’t get the chance to do as much as I’d like. It seemed counterintuitive: I was exercising so I could be around longer for my kids, but I was doing it during the time that I could have been spending with them now.

I would go to bed late after work, panicked about having to get up in four hours, then lie in bed fully awake until it was time for the personal-training session. I would go and exercise, feel great about what I had achieved for the next hour, and then spend the rest of the day feeling shattered. The breaking point was when I realised that I could cancel at the last minute, as long as I paid for the session. I was soon paying a lot of money to wake up and text a man to say that I wasn’t going to be able to see him, before going back to sleep.

I tried a couple of other things. I started going to the gym on my own; I tried to run; I did boxing training. Running was boring; I spent most of my gym time downloading albums on to my phone; and one day after boxing I threw up round the side of the house and felt so ill I was late for work. It wasn’t exactly a sustainable way to keep fit, especially as there is only a finite number of things to keep being shit at.

Then I discovered my saviour: a spin bike with a screen that lets you do classes online. That doesn’t sound particularly enticing to a sloth, but it was perfect. I could do high-intensity classes, and all I had to do was go downstairs. You get little electronic badges for keeping up a streak, and a T-shirt when you complete 100 classes. There was an accompanying Facebook group full of people who post photos of themselves after a ride saying things like, “Go, team!”

I felt pretty weird about doing something so culty, even before the creepy Peloton Christmas ad that looked a lot like a sequel to Get Out. It is also supremely expensive, with a huge outlay on the bike, plus a gym membership-sized subscription – so much so that my wife and I had a meeting to discuss whether it was worth it, based on my predilection for abandoning everything. I found the conversation so unfair that I went and made a smoothie with the NutriBullet, which I eventually found behind my Slendertone Ab Tuning belt. However, the spin bike is the one form of exercise that has stuck. It is difficult to find an excuse not to exercise in your own house (plus my wife has threatened to leave me if I stop using it).

Facebook Twitter Pinterest ‘In August I had to go on tour, which threw everything up in the air.’ Photograph: Pål Hansen/The Guardian

Diet was the next thing. I tried to take all of the decision-making out of my hands by having pre-prepared meals delivered. I would eat only three meals a day, plus water, and know exactly what my nutritional intake was. The food sounded very cool: dishes such as Sichuan tofu with spicy pak choi. It was tasty and convenient, but seemed like something a professional athlete would do rather than someone who occasionally uses an exercise bike. Also, it was a bit weird to rule yourself out of every social occasion that involved eating because you were living out of Tupperware boxes. But the main stumbling block, again, is that it is prohibitively expensive – exorbitant enough for my wife to start calling me Jay-Z.

In the end, I settled on intermittent fasting. I am going to hold my hands up here: I don’t understand the science behind it. You select eight hours of the day when you can eat, and fast for the other 16, sticking to zero-calorie drinks such as water or black coffee. After 12 hours of not eating, your body apparently goes into a state in which it’s eating itself, or something. I don’t know. What I do know is that I definitely benefited from reducing the number of hours in which I was allowed to take in calories. You can also, if you fancy, only do it six days a week and have a cheat day, although I made the mistake of deciding ad hoc when my cheat day was going to be, before eventually realising I had had seven cheat days out of the last 10. I knocked cheat days on the head.

I am trying to stay healthy because it feels good; because eating better makes me better at work

I would love to tell you that the rest of the year was spent smashing out class after class, as I intermittently fasted my way to a set of chiselled abs and being sexy AF, but life got in the way. In August I had to go on tour, which threw everything up in the air.

I hate having food in my system when I’m on stage. This means I don’t feel comfortable eating anything after about 5pm, if I’m due on at 8pm. While this is great for minimising calories in the afternoon, I often finish my show contemplating eating a member of the audience. As everyone knows, no good nutritional decisions are made at 10pm. I would often end up going for a curry, so hungry that I would eat 1,000 poppadoms before the actual food arrived.

I attempted to stock my hotel room with healthy choices for after the show. However, I was struck by the bleakness of eating a quinoa salad at 11pm in my underwear. I suppose it is possible to put on some clothes, but I made a vow many years ago that I would only ever eat in a hotel room in my underwear and I would hate to break that streak.

I came up with a compromise. I decided to push myself to eat a little bit closer to the show, and then nothing afterwards. This was OK as long as I didn’t do anything that made me hungry, like sit at a bar that had snacks, peruse the room service menu, or talk to anyone who had a head shaped like a potato. This meant I had to avoid my tour manager, or King Edward as I started to call him.

Facebook Twitter Pinterest ‘I am by no means an exercise beast.’ Photograph: Pål Hansen/The Guardian. Prop Stylist: Vicki McLean. Grooming: Lou Rothwell at Represented By. Scales Supplied by Healthcheck Services Ltd

Staying on top of exercise was also difficult without my spin bike. I have to confess to finding hotel gyms horribly intimate. More often than not, they are like a cupboard with equipment inside. You find yourself in close proximity to a stranger, constantly apologising for going to pick up the same piece of equipment. On one occasion, another man seemed to be doing a circuit that involved every piece of equipment in a random order. I had to gamble and go for the thing I hoped he might not be using next. It was only after about 45 minutes of this that I realised he was probably thinking the exact same thing.

I needed a strategy that meant I could avoid a hotel gym and, of course, something that worked in hotels that didn’t have one. I searched online and, as it turns out, hotel room workouts are in high demand. After a little more searching, I found myself doing a set of chest presses with my suitcase. It is as ridiculous as it sounds, but you do feel a bit of pride at having made the best of a bad situation. And by bad situation, I mean having such a bounty of nutrition in your life that you have to find ways to burn it off when you’re slightly too shy to use the on-site gym at your luxury hotel.

If I am giving the impression that I have worked relentlessly at getting my weight down, please be reassured: I have lost a bit of weight, but spent more time feeling guilty about doing nothing than making progress. Weeks have gone by where I was too knackered to do anything; once, I felt so sorry for myself that I ordered a vegan sticky toffee pudding to my room at 2am and ate it in the dark. And then went to sleep. And then woke up and found I had toffee on my chest. And then ate that toffee.

But I have become much more conscious of my choices. When I make bad ones, I try to make some good ones for a while. I no longer see eating sticky toffee pudding at 2am as a terrible failure; it just means I need to balance that afterwards. I am by no means an exercise beast, but I do try to look for opportunities to work out when I can. Before, I would have described myself as “sedentary with occasional flurries of exertion”. I have also stopped thinking about it as “falling off the wagon”; it’s just an ongoing thing that you do your best at, and then try to describe in a Guardian column without sounding like Carrie Bradshaw in Sex And The City.

And without being too corny, I have become more invested in the process because it gets results: I am trying to stay healthy because it feels good; because eating better makes me better at work; and because exercise is good for my mental health. I use these things to help me get over the fact that there is still no way I am ready to wear that Wu-Tang T-shirt yet.

I think the thing I am most grateful for, however, is pushing my belly out so excessively in the “before” photos (page 12) that it looks as if I’ve made huge changes. I tend to think of it more a gear change.

Joe Wicks’ hotel room workout

These exercises can be done anywhere – all you need is a small space and a chair. They should be done in a circuit. Spend 30 seconds on each one, and then have 30 seconds rest. Repeat five times, making sure everything is done in a controlled way with a straight back and engaged core.

Squats

With your feet shoulder-width apart and your back straight, squat low towards the ground and back up again.

Press-ups

Start in a plank position and lower your body towards the ground by bending your arms. Then, straighten your arms, pushing yourself back up into the plank.

Running on the spot

Make sure you lift your knees as high as you can, and pump your arms as fast as possible. Do this for 30 seconds, keeping your back straight.

Lunges

Start with your feet together. Take one leg back, bend your knees and do a reverse lunge. Then straighten your back leg and stand up, putting your feet back together. Alternate between the right and left leg.

Tricep dips

With your back to a chair, move your hands behind you so you are holding the top of it and lower your body towards the ground by bending your elbows. Then push yourself back up again by using your triceps – the large muscles on the back of the arms. Repeat this exercise slowly for 30 seconds. As told to Grace Davis

● Find The Body Coach TV and Joe Wicks on YouTube

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• This article was amended on 6 January 2020. An earlier version referred to a “mesosaur” in the film Jurassic World, when a mosasaurus was meant.