I will not be tasting Cadbury’s new “diet” Dairy Milk – containing 30% less sugar than the original bar – because I am on a diet-diet. It is a very strict diet consisting of not ever going on a diet, not listening to people talk about diets and not consuming anything with the word “diet” on it. My goal is to shed approximately 20 years of self-hatred, body shame, and a disordered relationship with food. And I can tell you now – it is working.

I dieted from when I was eight years old until I was 24, and I ended up fatter. I have since learned that my body is perfect just the way it is, and I am now happy, all down to the diet-diet: the diet to get you off diets for ever.

Unlike all other diets, it does not demand your time or money. All you have to do to succeed is not diet. It is surprisingly easy – and healthy, by the way. We have known for decades that diets do not work: 95% of “successful” dieters regain their lost weight within five years. There is also an association between dieting and disordered eating , starvation and use of untested diet pills and laxatives.

Roughly speaking, healthy eating is a varied diet, full of vegetables; listening to your body; and exercising for 30 minutes a day. But we do not want to be healthy, we want to be thin. We also conflate being thin with being happy. Chocolate, meanwhile, is a “guilty pleasure”, a “vice”, an “indulgence”, and all these other negative connotations we force upon food that doesn’t make us thin.

Now Cadbury has joined the dieting trend. What’s next? Santa Claus being forced to lose weight for “promoting obesity”? Selling only fruit in cinemas? Let me ask you this: have you ever tried to watch a thriller as the person next to you glubs down a peach?

Our obsession with weight loss and dieting is unhealthy, and doesn’t actually make us thin or happy. Quite the opposite, actually: it is dangerous. But dropping the sugar content of a 100g chocolate bar from 56g to 39g won’t make you thin. It was never that 17g of sugar holding you back from wearing a bikini on the beach. Cadbury’s new, lower-sugar Dairy Milk is just another reminder that chocolate is bad and we should be ashamed of enjoying it. And I am sorry, but that is not allowed on my diet-diet.

Happy Fat: Taking Up Space in a World That Wants to Shrink You is published by 4th Estate. To order a copy for £11.43, go to guardianbookshop.com. Sofie Hagen is touring the UK in 2019 and 2020.