As he has written and spoken passionately about the unhealthy foods that he believes are a threat to our national welfare, he was agonised about what such obsession might do to some people. “I have in the last two years become extremely anxious about the risk of driving eating disorders and food anxiety. And so I teach a lot now about eating disorders and I work with eating disorders academics.”

In a new BBC documentary, Van Tulleken, who has previously made programmes with his twin brother, Xand, who is also a doctor, looks at why we are all eating so much ultra-processed food. It is not our fault, he argues, “It is the food.” We just can’t stop eating it, and many of us are addicted to it.

Van Tulleken studied medicine at the University of Oxford and is an infectious diseases doctor at the Hospital for Tropical Diseases in London and an associate professor at UCL. He works with Unicef and the World Health Organisation, and will be giving this year’s Christmas lectures at the Royal Institution.

We are facing a “health catastrophe” of obesity and other diseases caused by what we consume, he says. “Our diet-related disease statistics are as bad as the worst in the world. We have to take immediate action. It’s a chronic emergency. We’ve been in a state of emergency now for at least a decade. The pandemic of diet-related disease — primarily obesity, but also lots of other problems including cancers and metabolic disease like type 2 diabetes — is driven by the marketing, availability and consumption of industrially prepared and processed products that are high in energy, salt, sugar and fat.”

A father of three young daughters, Van Tulleken, 46, is alarmed by the obesity levels in children. Recent figures show that 12 per cent of children aged two to ten are obese.

He used to keep a bowl of sweets and chocolate in his house to offer guests. “The kids were eating quite a lot of it and so we’ve got rid of most of it. I do think that it’s very important for children to have a normal life. And so when they go to a party they eat the same food that everyone else does. They’re allowed to eat anything but we don’t have much of [the unhealthy stuff] in the house.”

There is one thing that experts on eating disorders agree on, he says. “If you want your kids to develop good eating habits, sit down with them at meals and role-model good eating. Eat off china plates with cutlery, eat real food and do it yourself in front of them. I’ve taken that quite seriously.”

Twice as many children from deprived backgrounds are overweight than those from wealthy areas. And Van Tulleken points out that cooking proper meals is harder for the million families in Britain who do not have access to proper refrigeration or cooking facilities.

But while wealthier families may be eating fancier ultra-processed food, perhaps with fewer additives, “we’re all eating it, constantly”.

For some people, industrially processed foods are addictive, Van Tulleken says. He has patients who have told him of their experiences. “If there is something that you know harms you in some way, and yet you keep doing it despite trying to stop, whether it’s an activity or a substance, that’s what an addiction is.” One woman tells him in the documentary how she gorges on mixing bowls full of sweet cereal and bars of chocolate. “Most people will not get addicted. But the rate of addiction across cocaine, alcohol, tobacco and ultra-processed food is all about the same: 10 to 20 per cent of people, having tried it, can’t quit.”

In his new documentary he tracks down some of those who were on the inside as the food industry built ultra-processed food brands over several decades. “In the 1970s people think I revolutionised the food industry,” says Howard Moskowitz, an experimental psychologist who helped many companies find the “bliss point” in their products by adding just the right levels of sugar, salt and fat.

Professor Francis McGlone, former lead neuroscientist at Unilever, explains how he used brain scanners to test people’s reactions to foods. Images of the reward system area of the brain glowing like a furnace were used to tell the story that ice cream makes people happy. McGlone also outlines the way softer foods make people feel less full, providing an opportunity for what he calls “scurrilous behaviour”: making food softer so people eat and buy more of it.

Much thought and expense go into packaging products. Professor Barry Smith, a sensory scientist, explains that when he was advising the manufacturer of Pringles, they were worried about competition from Doritos and had the idea of making the tube bigger. “I said, ‘No, no, no, no, don’t do that. People like struggling to get their hand in. They’re like foraging bears. Searching out something to eat — that’s increasing your desire.’”

Van Tulleken suggests that all this corporate creativity means parents are almost powerless. “When you worry about your kids, remember that whatever you do, there has been a team of geniuses working on product development and marketing over many, many decades. Whatever you’re sweating about as a parent, it’s probably not going to work. So maybe don’t fuss about it too much.”

In the course of her research into ultra-processed food, Dr Laura Schmidt, professor of health policy at the University of California, delved into the archives of RJ Reynolds, the tobacco giant. She showed the documentary makers a 1962 memo from the head of the company’s labs to the CEO, which said RJ Reynolds was not just a tobacco company: it was “in the flavour business”.

“I had drawn comparisons between tobacco and ultra-processed food and been called out on it,” Van Tulleken says. “People were like, ‘How can you stigmatise this food?’”

He references a study published in the journal Addiction last year which found that in the decades when the big tobacco companies owned food companies, their food products were more likely than those made by other companies to be “hyper-palatable” — a phrase used for fatty, salty, sugary foods that activate the reward regions of the brain.

“We need to think of food and alcohol in the same terms, using the same regulatory framework, as we think about tobacco,” Van Tulleken says. The government has said it plans to introduce a 9pm watershed for “junk food” TV advertising. They are making the right noises, Van Tulleken says, but “revolutionary thinking” is required. The mission should be to get childhood obesity rates down to 1990 levels. “It was 5 per cent. Still unacceptably high, but that should be the goal.”

The voluntary traffic light system on food products to warn about levels of fat, sugars and salt is confusing “nonsense” and Van Tulleken would like to see it replaced with a system like that used in several South American countries. There, black octagons say “high in calories” or “high in salt”. There is evidence sales of such products have reduced.

But he warns that a unified plan is needed. “Labelling of products with warning labels will not solve the problem. Marketing restrictions won’t solve the problem. Avoiding [such foods] in schools won’t solve the problem. You have to do everything all at once.”

That includes controversial moves. “You’re going to have to tax chocolate bars. You can’t make a food security argument that chocolate bars are important for solving hunger. They need a proper tax just as we’ve done with soft drinks.”

Defenders of industrially produced food say that products created with the ingredients required to keep products on the shelves without rotting are essential for our food security. Much of that shelf food is “not compatible with healthy life”, and Van Tulleken scoffs at the food security argument. “Food insecurity in Britain is going up. We have food banks that didn’t exist when you and I were kids. The food is cheap, that is true. But it’s very, very expensive later on. We will pick up the bill for the health costs.”

Kids need to be better educated about cooking and nutrition, but it is not a top-five priority for him. “It was an educated generation who’d been taught home economics and made their own food that had their diets destroyed by the food industry. We should have an education system built around food. But as long as there are five chicken shops on the way from your house to school, it’s all a little bit … I don’t know about futile, but you have to deal with the food environment too.”

He is scathing of the way the food industry has involved itself in healthy-eating education, observing that one of the supporters of the British Nutrition Foundation’s healthy-eating week last year was Coca-Cola. Too many expert scientists on healthy eating have conflicts of interest with ultra-processed food companies, he believes.

There are powerful people in the food industry who would rather like Chris van Tulleken to shut up. After the publication of Ultra-Processed People, one food company offered him £20,000 just to come and talk to them for a couple of hours. When he examined the contract he found that he was being asked to agree never to say anything that could damage the reputation of the company, its products or its customers. Realising he would be “silenced by the contract”, he declined.

Another email arrived from McDonald’s, exploring the idea of him becoming an ambassador and inviting him to fly to the headquarters in Chicago to meet the board. He said he would like to talk to them but he would pay his own way, and he wouldn’t even let them buy him a burger. “Then they cancelled the invite.”
Irresistible: Why We Can’t Stop Eating is on BBC2 on November 25 at 9pm and will also be available on BBC iPlayer

Ultra-processed food glossary

The bliss point
The amount of sugar, salt or fat that makes food irresistible.

Vanishing caloric density
Foods that melt in your mouth and signal to your brain that you’re not eating as much as you are.

Sonic branding
The expression of a brand through signature sounds.

Snackification
The phenomenon of people increasingly consuming smaller meals instead of three meals a day, driven by producers increasing their launches of snacking formats.

Stomach share
The amount of digestive space a company can grab from the competition.

Ultra-processed food
Packaged food made using ingredients and processes you couldn’t replicate in your own kitchen.

Hyperpalatable
Food combining unnatural levels of fat, sugar or carbohydrates that can encourage overeating.

Line extension
When a slightly different product is created from an existing product line in order to increase consumption.