In 2008 Jess Ainscough, an Australian magazine journalist, was diagnosed with a rare form of cancer, epithelioid sarcoma. Rather than undergo the drastic treatment prescribed by her doctor, amputation of her arm and shoulder combined with chemotherapy, she decided to combat the illness with something called Gerson Therapy, which involved drinking vegetable juice with coffee enemas four times day. Styling herself “The Wellness Warrior”, she charted her progress on a blog, which became a sensation. When her mother was diagnosed with breast cancer in 2011, she decided to shun conventional treatment and follow her daughter’s regime. Ainscough’s mother died in 2013 and her own cancer, a slow-moving type, which is why she believed her diet to be working, began to spread; she died in 2015. With conventional treatment both women might be alive today.

It’s stories like this that make chef Anthony Warner angry. So angry that he started a blog in 2016 to debunk food myths called The Angry Chef. Now there is a book and he is still mad as hell. There is a direct connection, Warner believes, between the harmless-sounding woo-woo of Gwyneth Paltrow’s “wellness adventure” and the Hemsley sisters’ “healthy eating” and the unnecessary deaths of Ainscough and her mother: “the end point of that stupid, pointless detox salad you chose for lunch lies here. It is people claiming they can cure deadly disease with carrot juice and enemas.”

Warner studied biochemistry at university and has worked as a development chef in the food manufacturing industry. In short, he knows his onions and his big beef is with the idea that some foods are good while others are bad. Often when people become unwell their first thought is that it relates to their diet. Indeed, Ainscough blamed hers for her cancer: “I was living a life of excess and disconnecting myself from nature, which eventually led to my body manifesting cancer,” she wrote on her blog.

‘Detox is pseudoscientific bullshit’. Photograph: Luke Wilcox/Alamy

One by one Warner demolishes popular food myths: sugar “is demonised to an extent that is at best unhelpful and at worst irresponsible”; “detox isn’t real”, it’s “pseudoscientific bullshit”; it is not blueberries – even the wild ones from Maine that Paltrow recommends – that cleanse our bodies: we have liver and kidneys that effectively remove toxins. On the favourite of many celebrities, the alkaline diet, he writes: “Followers of the alkaline diet need to understand that in accepting the diet’s philosophy they are rejecting the whole of mainstream science.” That’s you, Jennifer Aniston!

So why do so many people fall for this nonsense? Partly because “sensible talk of moderation, small improvements and slow incremental changes will never create anecdotes as powerful and emotive as pseudoscience”. We are not helped by some journalists with very little grasp of science who sensationalise scientific papers. Even a number of scientists are complicit, thanks to their hunger for publicity.

But Warner goes further, into heretical territory. He asks difficult questions about the middle class belief that convenience or processed food is somehow unhealthy. Starting with Michael Pollan’s famous dictum – “don’t eat anything your great-grandmother wouldn’t recognise as food … if it came from a plant, eat it; if it was made in a plant, don’t” – Warner argues that our great-grandmothers would probably have eaten poorly, with little fresh produce and no understanding of the importance of vitamins. And as Jonathan Meades points out in his recent cookbook: “homemade begs one question. Whose home? Have you ever actually seen people’s homes? Why should biscuits made at home be better than those baked in a factory, a factory that specialises in biscuits?” Much of what we think of as healthy eating is more about status than wellbeing: “Clean eating seems deliberately designed to be expensive, exclusive and difficult to achieve,” Warner says.

Although this gleeful trashing of foodie shibboleths is engaging – I’d like to read the Angry Chef on organics – the book reads as if it was assembled in a hurry, and the sweary shtick that is so bracing in the blog becomes rather wearing here. Warner keeps telling us how cross he is, but his research, analysis and humour make his points far more eloquently. Yet this remains a book that will allow you to enjoy food with less guilt; it might even save lives.

• Henry Jeffreys’s Empire of Booze is published by Unbound. The Angry Chef is published by Oneworld. To order a copy for £11.04 (RRP £12.99) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.