Walk into any supermarket and the choice of foods is enormous, from brightly coloured breakfast cereals to pre-packed lasagnes. But for many, deciding what to add to the basket has never been harder, as concerns grow over industrially produced items. You might think Dr Chris van Tulleken, as the author of the bestselling book Ultra-Processed People – an investigation of how aggressively marketed products created by the food industry are packed with ingredients engineered to make us overeat – would be just the person to ask for help. But you would be wrong. “One of my really important things that I try never to do is give anyone advice,” he says. “If someone’s standing confused in a supermarket, I will just say, as someone who studies this stuff, is a medical doctor and a scientist, I find it all terribly confusing.” Perhaps it is unsurprising then that in presenting this year’s Royal Institution Christmas lectures, Van Tulleken wants to explore how what we eat has shaped our evolution, affecting everything from our immune systems to the anatomy of our jaws. “I want people to come away with an understanding of what the project of eating is, of how their ancestors – all the way back to the dawn of life – ate, and how we turn other living things into movement and thought and energy in general,” Van Tulleken says. As is fitting for a TV presenter known for “gross” experiments on the BBC children’s programme Operation Ouch, there will also be plenty of fun facts – while a cow has four stomachs, a platypus has none – special guests and, of course, experiments. “I think it’s safe to say you will be getting views that you have probably never seen before of different parts of my digestive tract,” Van Tulleken says. It will not be the first time he has tried things out on himself: as part of one experiment he spent a month where 80% of his calories came from ultra-processed foods (UPFs). While the full definition of what constitutes a UPF is lengthy, Van Tulleken has said in general they are plastic-wrapped and contain ingredients not typically found in a domestic kitchen. And they make up a vast proportion of our diets: research suggests a typical teenager gets around two-thirds of their calories from UPFs. “Slowly, I think I started to worry about the food, and then it suddenly became disgusting,” he says of that experiment. “So these days I eat it to be polite, because you can’t avoid it, but other than that, I actually don’t like eating it.” Yet while many studies have shown the associations between UPFs and poor health, unpicking how they may actually be causing harm is far from easy. “I suspect that most of the harm is from the fat – saturated fat – salt and sugar and energy,” says Van Tulleken. But while he says nutrient content offers a useful way to regulate UPFs, it is not the only factor in play. “What we know about ultra-processed food from industry testimony and from experimentation is that the food is engineered to drive excessive consumption, and so not only are you eating food with more fat, salt and sugar, you’re also eating more of that food,” he says. Scientists have suggested UPFs may disrupt the microbes that live in our gut and play an important role in the body’s digestive and immune systems. Van Tulleken will explore the importance of the gut microbiome in the Christmas lectures, yet he is sceptical of the growing range of companies – from Zoe to Viome – offering consumers the chance to have theirs analysed. His reservations, he says, are the same as those he harbours towards food companies. “My answer to the question about microbiome personalised technology companies is the same as my answer about the food companies and all the other companies: those companies exist for a single reason. They’re often very, very, very indebted to investors, and they have enormous growth requirements,” he says. “The science is constantly emerging. But put it this way. I’ve never sent my poo off to anyone, and nor will I be doing it.” Van Tulleken’s aversion to the food industry is clear, Yet he says he is not hoping to overthrow the system. “I am not an anti-capitalist,” he says. “My initial argument is for some very simple warning labels on food, a little bit of progressive taxation on the worst products.” Few scientists would argue with the concept of helping people to make healthier food choices. However, the concept of UPFs has come in for criticism, and some experts have argued that its fuzzy definition captures foods that are not that bad for you. While Van Tulleken disputes the benefits of such products, he admits there is a loophole. “It [the definition] doesn’t encompass lots of products that we think are probably pretty harmful,” he says, citing as an example a non-UPF frozen lasagne. Eating such food in a restaurant, however, is not the problem, he says. “The problem is industrially packaged foods, typically high in fat, salt and sugar and energy, that are aggressively marketed.” Yet the focus on mass-produced food has fed another criticism: that criticising UPFs is a form of food-shaming. There are also concerns that, just as the “clean eating” trend in the 2010s led some people to spiral into disordered eating, a heightened focus on UPFs may have a similar effect. Van Tulleken says he is very alive to the risks of stigmatising food and has worked closely with the eating disorders faculty at the Royal College of Psychiatrists, adding there is even evidence that some eating disorders may be associated with certain UPF products. These are chewy issues, but the Christmas lectures will be easier to digest. “They’re about grappling with the fundamentals of the most robust science around food and diet at the place that kind of invented how to communicate about all this,” says Van Tulleken. “I think being forced to reconsider it all across three lectures and do a really deep dive into the meaning of food and how it works – and getting to pull in other experts – I mean that that’s going to be really fun.” The Christmas Lectures from the Royal Institution (RI) supported by CGI will be broadcast on BBC Four and iPlayer in late December. The ticket ballot for the live filming opens to RI Members and Young Members on Thursday 12 September.