I never quite knew what the word “sophistry” meant, until I read this book. I had a vague idea that it was something to do with making a false argument. But I looked the word up and saw that this wasn’t quite right. Sophistry means the clever use of arguments that seem true. In Chaucer’s time, it used to mean cunning, or craft. The original ancient Greek sophists were people, according to Plato, who were virtuoso athletes of words. Above all, sophists are plausible. That’s what makes them so dangerous.

This is what came to mind reading the latest screed by Anthony Warner, who worked for many years at Premier Foods, one of the biggest food companies in Britain, which manufactures Mr Kipling cakes, Angel Delight desserts and Batchelors Super Noodles, among many other branded processed foods. Ten years ago, the Belfast Telegraph described Warner as TV presenter Loyd Grossman’s “Italian development chef” because Warner was the person who helped Grossman develop his own-brand pasta sauces. But that was before Warner transmogrified into “The Angry Chef”, the name of an expletive-ridden blog that he started writing in 2016 “exposing lies, pretension and stupidity in the world of food”. He could have called himself “The Angry Consultant to the Food Industry” but it wouldn’t have had quite the same ring. In 2017 the blog gave rise to a book, The Angry Chef: Bad Science and the Truth About Healthy Eating.

To begin with, many in food writing circles considered Warner a breath of fresh air. I was one of them, going so far as to write a blurb for the book, welcoming it as a “bracing and funny tirade against the nonsense and harm done by food fads”. I liked the way he skewered the quackery of alkaline diets and the absurd overuse of coconut oil and other so-called superfoods. I knew that Warner worked for the food industry, but I didn’t feel that this had an undue impact on his arguments. Maybe there was an element of “my enemy’s enemy is my friend” in my liking for Warner’s writing. Over the course of my life, too many people close to me have developed eating disorders and when Warner attacked the restrictive rules and “nutribollocks” of the clean eating trend, his anger seemed righteous.

But the more I read Warner’s blogs and articles (he is now a columnist for the Sunday Times), the more I started to find his anger oddly limited. He seemed to have plenty of fury for the “pretension and stupidity” of health bloggers and detox regimes but remarkably little anger for the food industry that has marketed sugary junk foods to vulnerable consumers, including children, on an unprecedented scale, with catastrophic consequences for human health. When I went back and reread The Angry Chef I was struck that, in between the funny parts about liars and charlatans, there were curious overstatements and binary oppositions. In Warner’s world, if you question the prevalence of sugar in our diets you are a prejudiced, judgmental, pseudo-scientific “nutrition expert”. “To give a child a bowl of breakfast cereal and a glass of orange juice is now to be a social pariah, guilty of the vilest abuse,” he writes. Really? If that were true, our eating habits would be very different.

And now we come to his new book on the causes of obesity, which suggests that everything you thought you knew about nutrition and weight is wrong. On first glance, there is much here that seems both plausible and just. For one thing, Warner recognises that obesity has complex and multifaceted causes and it is not – as so many persist in claiming – a collapse in willpower. Warner makes a plea to end the dreadful way in which people with obesity are stigmatised by the media. “Shaming fat people does not help them. It makes their lives harder. It makes their health worsen,” he writes. He is right about this. Throughout the book, Warner positions himself not so much as an angry chef as a cuddly teddy bear on the side of tolerance, love and compassion. He urges us to “stop judging people by how they look” and to relish the simple things in life such as sharing sandwiches in the park.

The strangeness of the book emerges when you start to examine what he is actually saying about the causes of modern obesity and, more widely, of diet-related illness such as type 2 diabetes and heart disease. He implies that it is not really about carbs, nor about sugar and anyone who suggests otherwise is probably some snooty middle-class person who shops at Wholefoods. He writes derisively of New York City mayor Michael Bloomberg’s “infamous (failed) attempt to halt the sale of supersize soft drinks” in the city (although Warner admits we do need to cut down a bit on sugar “if only because of the associated dental problems”). Obesity is also not really about microbes, Warner insists. He lambasts microbe expert Tim Spector for an experiment involving Spector’s student son showing that just 10 days of eating nothing but McDonald’s meals led to a 40% reduction in the diversity of his gut bacteria. This was a “shameless publicity stunt” Warner writes, and anyway, it proves nothing.

Warner also encourages us to discard the notion that obesity results from calorific confectionery being pushed on us in every supermarket and newsagent on a scale never seen in the past. The only reason that there is so much chocolate in the supermarket, according to Warner, is because of our moralising culture of guilt. “In places where Twix and Dairy Milk do not occupy the role of guilty pleasures, they fail to dominate the supermarket shelves.” This is pure sophistry. He does not mention the fact – which is no secret, if you read trade journals on confectionery – that the excessive quantity of sweets in our shops is part of a deliberate strategy by retailers and manufacturers to create “interruption points” as we walk around stores.

In Warner’s book, obesity is not about an over-supply of calories, and it is not about the rise of takeaways near schools or wider changes to our food environment, so there is little point in trying to reform the obesogenic environment we live in. “Often the environmental account is little more than a thin disguise for contempt,” he insists. “Mostly the idea is that fat people need to be coerced into more middle-class food options, cooking from scratch, meals round the table, less fried chicken, more hummus.” By equating sound advice with coercion, he makes it impossible to offer sound advice. It is possible to hate fat-shaming and still to want to apportion some of the blame where it belongs, with the food industry. But that’s precisely what Warner wants to rule out.

So what does he think caused the transformation of our bodies over the past few decades, if it isn’t food? Warner’s candidates include poverty, stress and poor housing. He is right that all of these factors strongly correlate with poor diets, but he always seems to miss out the part of the argument that brings eating into the equation. One of his preferred explanations for obesity is genes. His proposition is that “larger people go for larger people, and tend to produce more children when they do”. It is certainly true – as genetic studies involving twins have confirmed – that our individual responses to food, including our appetite, have a strong genetic component. But Warner does not have a convincing explanation for why either genes or poverty would suddenly be driving weight gain, given the rapid rise in obesity across the world from 1980 onwards.

At moments, his confusing arguments segue into outright inaccuracy. In Warner’s closing chapter, he writes about Amsterdam, which may be the only place in the world – outside of famine zones – where child obesity is actually declining. In 2012, the city’s deputy mayor Eric van der Berg launched the “Amsterdam healthy weight programme”, which included a whole tranche of measures, from workshops on healthy cooking for parents to bans on junk food marketing at sports events. In just four years, rates of child obesity fell by 12%. Amsterdam has become a beacon for nutrition campaigners around the world, proof that it is possible to make radical improvements to the environment in which children live and eat.

How did Amsterdam do it? Warner wants us to believe that the success was “unique to Amsterdam” and not much to do with food. He insists that Van der Berg saw that the “focus should not be on anything as trivial as what children were eating”. This is wildly misleading. If you look at the information given to families by the programme, it is very much about what children are eating (as well as about exercise, sleep and limiting the use of electronic devices). Children in Amsterdam are encouraged to avoid eating too much sugar and saturated fat and to eat four servings of vegetables and two of fruit every day, and to be active for at least an hour a day. The Amsterdam advice on children’s food is quite specific, urging parents to limit “crisps, croissants, chips, pizza, sausage rolls” as well as cookies, pastries, packaged snacks and soft drinks.

Warner also claims that in Amsterdam, “instead of getting rid of school vending machines selling sugary drinks, the decision was taken to allow them” while entrusting children to make “better decisions”. Again, this is an outright falsehood. One of the key elements in the Amsterdam programme was that at participating primary schools, children were allowed to drink only water and milk. “Drink water from the tap” has been one of the single biggest messages of the whole campaign, reinforced in schools and at home.

If you think that the question of what children eat is “trivial”, this is the book on obesity for you. It will chime with many people’s wish not to be lectured at by people who claim to know better, and goes to great lengths to absolve the food industry and its relentless marketing of processed food from playing any role in modern diet problems.

• The Truth About Fat is published by OneWorld. To order a copy for £13.19 (RRP £14.99) go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.