Industrially processed food is designed to be addictive. But what exactly is it doing to our bodies?

The second weekend of my diet I went on a camping trip with my brother Xand and my two brothers-in-law, Chid (Richard) and Ryan. We drove west from London toward Wales, stopping at Leigh Delamere services, a festival of Ultra Processed Foods (UPF). I bought Cool Original Doritos, two cans of Red Bull and packets of Skittles and Haribo Supermix for the rest of the journey.

We slept in a beautiful spot near a waterfall in the Brecon Beacons National Park, spoiled only by my waking dreams about food and my body. I imagined my blood had become thick and sticky, as if it had become too concentrated from the salt and sugar. I woke up early, feeling sad and unwell.

I diluted myself with some water and cheered up over breakfast looking at the ridge of mountains. We had Kellogg’s Crunchy Nut Clusters (with wholegrain and no artificial colours or flavours and a promotion for adults to go free at Legoland) and Alpen Original Recipe “naturally wholesome muesli”.

Ryan, an internationally renowned psychology professor from Australia, was astounded to see I was eating Alpen on my UPF diet: “What’s wrong with Alpen? It’s natural and wholesome.” I told him that it technically qualified as UPF because it has milk whey powder in it, an ingredient that isn’t typically used in home cooking.

He looked genuinely baffled. “But the mountains on the pack look pristine!” I responded that it was still UPF. Chid and Xand agreed. “Well, it tastes good,” he insisted. If the packaging can persuade Ryan, it can persuade anyone.

As we drove home, I got a phone call from a producer at BBC Radio. They wanted me to make a short radio documentary introducing people to the idea of UPF. It seemed like this documentary could maybe help us get funding for our study should we discover anything interesting from my 80 per cent UPF diet (funders love to know that the research they’ve sponsored will be communicated widely). It would also be an opportunity to build relationships with potential research collaborators. So, I got in touch with Kevin Hall, the author of the paper that tested Monteiro’s hypothesis to see if UPF did in fact cause weight gain.

I called Hall from a soundproof radio booth in Broadcasting House and asked him about his experiment. “When I first came across this idea – that we should not be concerned about the nutrients in our food, but about the extent and purpose of the processing – I thought it was absolute nonsense,” he told me. It was a surprising start.

Hall was in his office in Bethesda, Maryland, where he is a senior investigator at the US National Institute of Diabetes and Digestive and Kidney Diseases. His somewhat bureaucratic job title – “section chief: integrative physiology section, Laboratory of Biological Modeling” – belies the fact he’s one of the major figures of 21st-century nutrition science, despite not being a trained nutritionist. He’s a physicist with a PhD in mathematical modelling – something called non-linear dynamics.

Born in Canada to blue-collar British parents – his father was a skilful machinist who built turbines for some of the first nuclear power stations, while his mother was an administrative assistant at a physiotherapist office – Hall was, like Carlos Monteiro, the first in his family to go to university. Hall excelled during his undergraduate physics degree at McMaster University, ranking near the top of his class in high-energy particle physics. He is characteristically modest discussing his achievements there: “The guy at the very top found it all so effortless, I realised I’d need to find something I was better at.”

He got a summer job in an electrophysiology lab, studying how dog guts organise their contractions. It was there that he started building mathematical models of biological processes, which diverted him into the field of nutritional research, which he subsequently transformed.

“Depending on who you run into, I’m known for one of three things,” Hall told me. He laid these out neatly.

First, there is his mathematical model of adult human metabolism. Using models like this Hall predicted several years ago that a low-carb diet would not have a significant effect on weight.

His next achievement was to test this model against the idea that had been growing since the turn of the millennium, that sugar was the main problem when it came to obesity. He did some of the defining work on how sugar affects our metabolism, which we’ll look at later.

Then there was his “Biggest Loser study”. For this, Hall followed the participants in the smash-hit American TV series, The Biggest Loser, for six years. They all started the programme with a BMI of greater than 40 – class 3 obesity (or, as it used to appallingly be known, “morbid” obesity) – and were then isolated for several months on a ranch where they were subjected to a programme of extreme calorie restriction and exercise. At the end of the competition, mean weight loss was around 60kg. Six years later, mean weight regain was 41kg, despite participants maintaining high levels of exercise. Hall’s study underlined the enormous difficulty in maintaining weight loss.

“And, finally, my work on ultra-processed foods … I guess it’s four things, in fact,” Hall said. This last study was why I was speaking with him. I certainly hadn’t been expecting him to start by saying he’d originally thought that Monteiro’s UPF theory was nonsense. He told me that he was at a conference, sitting next to a Pepsi executive when he first heard about UPF. This was back in 2017 when a few papers on UPF were starting to appear: “[The Pepsi executive] said there was this new way of thinking about foods that they were concerned about, and they wanted to get my opinion on it. My initial response was: how could anyone take it seriously?”

From Hall’s perspective, there had been decades of important progress in discovering which nutrients in our food supply are good (and bad) for us and how to cure diseases of deficiency. “Nutrition science,” he continued, “is called nutrition science because it’s about the nutrients, right? And here comes this Monteiro group saying, ‘No, no, no, you’ve got it all wrong.’”

He particularly didn’t like the way Monteiro described UPF as “formulations of mostly cheap industrial sources of dietary energy and nutrients, plus additives, using a series of processes and containing minimal whole foods”. He thought it was a fuzzy, unsatisfying definition that didn’t say anything about what the problem with these foods actually was

Excerpted with permission from Ultra-Processed People: Why Do We All Eat Stuff That Isn’t Food...and Why Can’t We Stop?, Chris Van Tulleken, Penguin.