Madeleine Shaw promoting her book Get the Glow. Photograph: Joe Pepler/REX/Shutterstock
But I only see the positive, said Shaw, now wiping away tears. It was at this point that the audience, who were already restless whenever McGregor or I spoke, descended into outright hostility, shouting and hissing for us to get off stage. In a book shop after the event, as fans came up to Shaw to thank her for giving them the glow, I too burst into tears when one person jabbed her fingers at me and said I should be ashamed, as an older women (I am 43), to have criticised a younger one. On Twitter that night, some Shaw fans made derogatory comments about how McGregor and I looked, under the hashtag #youarewhatyoueat. The implication was that, if we were less photogenic than Shaw, we clearly had nothing of any value to say about food (never mind the fact that McGregor has degrees in biochemistry and nutrition).
Thinking about the event on the train home, I realised that the crowd were angry with us not because they disagreed with the details (its pretty clear that you cant have sugar in sugar-free recipes), but because they disliked the fact that we were arguing at all. To insist on the facts made us come across as cruelly negative. We had punctured the happy belief-bubble of glowiness that they had come to imbibe from Shaw. Its striking that in many of the wellness cookbooks, mainstream scientific evidence on diet is seen as more or less irrelevant, not least because the gurus see the complacency of science as part of what made our diets so bad in the first place.
Amelia Freer, in Eat. Nourish. Glow, admits that we cant prove that dairy is the cause of ailments ranging from IBS to joint pain, but concludes that its surely worth cutting dairy out anyway, just as a precaution. In another context, Freer writes that Im told it takes 17 years for scientific knowledge to filter down to become general knowledge, while advising that gluten should be avoided. Once we enter the territory where all authority and expertise are automatically suspect, you can start to claim almost anything and many #eatclean authorities do.
That night in Cheltenham, I saw that clean eating or whatever name it now goes under had elements of a post-truth cult. As with any cult, it could be something dark and divisive if you got on the wrong side of it. After Giles Yeos BBC programme was aired, he told me he was startled to find himself subjected to relentless online trolling. They said I was funded by big pharma, and therefore obviously wouldnt see the benefits of a healthy diet over medicine. These were outright lies. (Yeo is employed by the University of Cambridge, and funded by the Medical Research Council.)
Its increasingly clear that clean eating, for all its good intentions, can cause real harm, both to truth and to human beings. Over the past 18 months, McGregor says, every single client with an eating disorder who walks into my clinic doors is either following or wants to follow a clean way of eating.
In her new book, Orthorexia, McGregor observes that while eating disorders long predate the #eatclean trend, food rules (such as eating no dairy or avoiding all grains) easily become a guise for restricting food intake. Moreover, they are not even good rules, based as they are on unsubstantiated, unscientific claims. Take almond milk, which is widely touted as a superior alternative to cows milk. McGregor sees it as little better than expensive water, containing just 0.1g protein per 100ml, compared with 3.2g per 100ml in cows milk. But she often finds it very difficult to convince her clients that restricting themselves to these clean foods is in the long run worse for their health than what she calls unrestrained eating balanced and varied meals, but no panic about the odd ice cream or chocolate bar.
Clearly, not everyone who bought a clean-eating book has developed an eating disorder. But a movement whose premise is that normal food is unhealthy has now muddied the waters of healthy eating for everyone else, by planting the idea that a good diet is one founded on absolutes.
The true calamity of clean eating is not that it is entirely false. It is that it contains a kernel of truth, as Giles Yeo puts it. When you strip down all the pseudo babble, they are absolutely right to say that we should eat more vegetables, less refined sugar and less meat, Yeo said, sipping a black coffee in his office at the Institute of Metabolic Science in Cambridge, where he spends his days researching the causes of obesity. Yeo agrees with the clean eaters that our environment of cheap, plentiful, sugary, fatty food is a recipe for widespread obesity and ill health. The problem is its near impossible to pick out the sensible bits of clean eating and ignore the rest. #Eatclean made healthy eating seem like something expensive, exclusive and difficult to achieve, as Anthony Warner writes. Whether the term clean is used or not, there is a new puritanism about food that has taken root very widely.
A few weeks ago, I overheard a fit, middle-aged man at the gym berating a friend for not eating a better diet a conversation that would once have been unimaginable among men. The first man was telling the second that the skinny burgers he preferred were nothing but shitty mince and marketing and arguing that he could get almost everything he needed from a diet of vegetables, cooked with no oil. Fat is fat, at the end of the day, he concluded, before bemoaning the idiots who tried to eat something wholesome like a salad, then ruined it by adding salt. If you have one bad diet day a week, you undo all your good work.
The real question is how to fight this kind of diet absolutism without bouncing back to a mindless celebration of the modern food environment that is demonstrably making so many people sick. In 2016, more than 600 children in the UK were registered as living with type 2 diabetes; before 2002, there were no reported cases of children suffering from the condition, whose causes are diet-related.
Our food system is in desperate need of reform. Theres a danger that, in fighting the nonsense of clean eating, we end up looking like apologists for a commercial food supply that is failing in its basic task of nourishing us. Former orthorexia sufferer Edward L Yuen has argued in his 2014 book, Beating Orthorexia that the old advice of everything in moderation no longer works in a food environment where eating in the middle ground may still leave you with chronic diseases. When portions are supersized and Snickers bars are sold by the metre (something I saw in my local Tesco recently), eating normally is not necessarily a balanced option. The answer isnt yet another perfect diet, but a shift in our idea of what constitutes normal food.
Sales of courgettes in the UK soared 20% from 2014 to 2015, fuelled by the rise of the spiraliser. But overall consumption of vegetables, both in the UK and worldwide, is still vanishingly small (with 74% of the adult UK population not managing to eat five a day). That is much lower than it was in the 1950s, when freshly cooked daily meals were still something that most people took for granted.
Among the affluent classes who already ate a healthier-than-average diet, the Instagram goddesses created a new model of dietary perfection to aim for. For the rest of the population, however, it simply placed the ideal of healthy food ever further out of reach. Behind the shiny covers of the clean-eating books, there is a harsh form of economic exclusion that says that someone who cant afford wheatgrass or spirulina can never be truly well.
As the conversation I overheard in the gym illustrates, this way of thinking is especially dangerous because it obscures the message that, in fact, small changes in diet can have a large beneficial impact. If you think you cant be healthy unless you eat nothing but vegetables, you might miss the fact that (as a recent overview of the evidence by epidemiologists showed) there are substantial benefits from raising your fruit-and-veg intake from zero portions a day to just two.
Among its many other offences, clean eating was a series of claims about food that were all or nothing which only serves to underline the fact that most people, as usual, are stuck with nothing.
Main photograph: Alamy
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