Dr. Chris Van Tulleken took part in a month-long experiment. He ate 80% of his calories from ultra-processed food. He explains what happened in his new book, Over-processed people.

Jonny Storey/Chris Van Tulleken

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Jonny Storey/Chris Van Tulleken

Dr. Chris Van Tulleken took part in a month-long experiment. He ate 80% of his calories from ultra-processed food. He explains what happened in his new book, Over-processed people.

Jonny Storey/Chris Van Tulleken

Eating processed food is nothing new. Humans have mashed grains to make bread thousands of years. But in recent decades, our food offering has changed, with an increasing number of ultra-processed products made with fillers, additives, stabilizers and synthetic ingredients that our grandparents wouldn’t have recognised.

A recent analysis of the Initiative for access to nutritionnotes that approximately 70% of food products sold in the United States are unhealthy, and much of the food can be classified as ultra-processed.

So, are we the frogs in the boiling pot, adjusting to the shift to ultra-processed foods, not realizing that these foods can promote overconsumption, which could harm us?

Amid the global boom in diet-related diseases, including obesity and type 2 diabetes, Dr Chris Van Tulleken, the author of Over-processed peoplemade himself a test subject for a short month-long experiment.

Van Tulleken, an infectious disease doctor in his 40s, traded his normal, healthy diet full of fruits, vegetables, lean proteins and whole grains for foods that came mostly from packages, boxes and bottles.

We spoke to Dr. van Tulleken about his book and his research.

This conversation has been edited for length and clarity.

How exactly has your diet changed: what did you eat?

I started eating more snacks, so I was snacking mid-morning. And I went back to eating the kind of cereal I loved as a kid, so I ate my breakfast cereal covered in chocolate. I drank more soda. And I made small exchanges, for example, instead of eating nuts as a snack I ate chips. And then I had a lot of ready-to-eat foods in the evening, so I still ate a few veggies, but I ate microwave lasagna or fried chicken or takeout pizza.

Overall, about 80% of my calories came from ultra-processed foods and it is very easy to do. Most of the bread in the supermarket is ultra-processed, nearly all of our breakfast cereals and snacks are ultra-processed, and most of our convenience foods are ultra-processed too.

Note: a classification system used by researchers classifies foods into one of four categories, from unprocessed and minimally processed, to ultra-processed.

In your book you describe how you gained weight, which isn’t too surprising given the foods you ate. Did you also measure what happened to your gut hormones, what did you find and how did you feel?

I felt very bad very quickly. I felt terrible. I stopped sleeping, developed anxiety and became very unhappy. I was the pilot patient in a study I’m conducting with colleagues at University College London. We found that there were effects on my gut hormones. So inside all of our bodies we have hormones that tell us when to stop eating. They are very well evolved. All animals have them, and ultra-processed food interferes with those hormones. So, at the end of a meal, my hunger hormones would still skyrocket.

This sounds very dramatic. Why do you think you were left wanting to eat more when you ate enough calories?

I think a lot of this food is designed to drive overeating. This food is full of energy. It is full of fat, salt and sugar. So you can consume calories at a much higher rate than if you eat whole foods. Additionally, ultra-processed food is often made into much smaller particles. So it could be absorbed in a different part of the intestine than the part that releases the fullness signal. So I suspect you’re eating this food faster than your body’s ability to send a signal to your brain saying, « I’m done now. »

This accords with evidence that foods high in refined carbohydrates such as bread, crackers and chips – which is basically what many ultra-processed foods are – can increase blood sugar and insulin which can stimulate appetite. What’s new here?

There is a very reputable scientist, Kevin Hall, in the United States. He conducted a clinical trial and found out when people eat an ultra-processed diet, eat about 500 extra calories a day, compared to people on a whole foods diet, who eat the same amounts of fat, salt, sugar and fiber. And there’s a lot of it epidemiological evidence this goes to show that it’s ultra-processed food that interferes with our body’s ability to say, « you know what, I can stop eating now. »

This was a small studio, 20 people. Are you investigating this further?

Yes, we were collecting data to get funding for a larger study we’re conducting.

Note: Van Tulleken and colleagues were recruit participants to study the effects of an ultra-processed versus minimally processed diet in the UK Researchers say it will be the longest-running dietary trial of ultra-processed foods and the first to help people reduce their consumption.

If ultra-processed foods had the same effect on everyone, wouldn’t we expect to see the entire population gain weight and become unhealthy, or do people react differently?

I think there are two groups of adults. Many people will have a relationship with ultra-processed food that is a bit like a relationship with alcohol. Many people can just enjoy two glasses of wine or a bottle of beer on a Friday night, and that’s fine. They can have that relationship with it. But many people will recognize that in reality their relationship with these food items is of a far more compelling nature.

But, as a society, can we really go back to whole food or diets composed of minimally processed foods?

There is no absolutely clear line between traditional food processing and ultra-processed foods. We chop, we cook, we smoke, we pickle, we salt, we grind, we pulverize: we’ve been doing all this for millennia and we have to do it. So processing is fine. But ultra-processing is where food is made in factories. It’s wrapped in plastic. It contains strange additives that you don’t find in kitchens. And the purpose of food is profit. So I eat cheese, but I don’t eat processed cheese. I eat butter, but I don’t eat margarine. I eat bread made with traditional flour, but I don’t eat emulsified bread from the supermarket.

The causes of obesity are many and some of them are related to food insecurity. People who have less to spend on groceries often buy the more shelf-stable processed food because it’s affordable. Do you think governments should step in to regulate?

We need governments to start treating products a bit like tobacco. We have to limit the marketing of these products and we have to change the labeling on the packaging. The simplest thing is to do what is Chile doing. They put a black hexagonal label on ultra-processed food packages. So governments shouldn’t ban it or tax the food, because it’s the only affordable food for many people. But governments can start warning people that it has negative health outcomes strongly associated with it.

Edited by Jane Greenhalgh for broadcast and web.