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What happened when a doctor only ate ultra-processed foods for a month

MARY LOUISE KELLY, HOST:

Diet-related diseases including diabetes and obesity are on the rise. So one medical doctor in England has set out to evaluate just how ultra-processed foods may drive up the risk. And he turned himself into his first test subject, eating a diet of junk food and sugary drinks. For our Living Better series, NPR's Allison Aubrey asked, what happened next?

ALLISON AUBREY, BYLINE: Chris van Tulleken is a doctor in his mid-40s who decided to swap his normal, healthy-ish diet for one made up of 80% ultra-processed foods for one month. Much of what he ate came packaged in bags and bottles, things like sugary cereals, chips, sodas and takeout foods.

CHRIS VAN TULLEKEN: It was a very severe change, so I became very unwell very quickly. I felt terrible. I stopped sleeping. I developed anxiety and became very unhappy.

AUBREY: It may sound pretty dramatic. And there could be a bit of exaggeration to his narrative, which he's documented in a book called "Ultra-Processed People." But he does weave in the latest science to make the case that much of what we buy in the grocery store, from the bread aisle to the snack-food aisles, fills us up with salt, sugar, fat and calories but doesn't really nourish us.

VAN TULLEKEN: The way of thinking about it is it's food that's been engineered to drive excess consumption. And that's why we can't stop eating.

AUBREY: That's what he experienced. And he says one of the most striking findings was the effect of his diet on his gut hormones.

VAN TULLEKEN: Inside all of our bodies, we've got hormones that tell us when to stop eating. They're 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 be sky high.

AUBREY: He was left wanting more despite having eaten plenty of calories. For breakfast, instead of his typical oatmeal and banana, he turned back the clock 40 years.

VAN TULLEKEN: And I went back to eating the kind of cereals I loved as a child. So I would eat, like, chocolate-covered Rice Krispies. I'd have more soda, but I often ate - drank diet soda pop. And then in the evening, I had a lot more convenience foods. I'd have microwavable lasagna, or I'd have takeaway fried chicken or pizza.

AUBREY: Within a month, he says he'd gained a bunch of weight, which isn't much of a surprise. All the sugar and refined carbohydrates can drive up appetite. But Dr. van Tulleken believes there's something more at play. He points to research done by a scientist at the National Institutes of Health who studied what happened when people ate an all-ultra-processed-food diet, compared to a whole food diet.

VAN TULLEKEN: He found that people eating ultra-processed food eat around 500 calories more per day, even when you compare them to control subjects eating the same amount of fat, salt, sugar and fiber, but on a whole food diet. So it is the ultra-processed food that interferes with our body's ability to say, you know what? I'm done. I can stop eating now.

AUBREY: Van Tulleken will now investigate this further with a study at University College London. He acknowledges, in some ways, there's nothing new about sugary cereals, junk food and sodas. But at a time when about 70% of foods sold in the grocery store are considered to be unhealthy, many people's diets are full of hyper-palatable, highly processed foods full of additives, fillers and unrecognizable ingredients.

VAN TULLEKEN: Many people will be able to have a relationship with ultra-processed food that's somewhat like a relationship with alcohol, where you might say, look, 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 about half the people listening will recognize that, actually, their relationship with these food products is much more addicted in nature.

AUBREY: This is part of what he wants to study going forward. Now, it's hard to abstain from eating ultra-processed food entirely. It's so ubiquitous in our food supply. But van Tulleken thinks governments should step in to help build awareness with new food labels.

VAN TULLEKEN: The simplest thing is to do what Chile are doing. You put a big black hexagon on ultra-processed food. And you don't ban it. You don't tax it. You can't tax this food because it's the only available and affordable food for many, many people in the U.S. and the U.K. But you can start to warn people that it has negative health outcomes strongly associated with it.

AUBREY: He says it is possible to return to a healthier way of eating by being much more aware of the foods we choose.

Allison Aubrey, NPR News.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Allison Aubrey is a correspondent for NPR News, where her stories can be heard on Morning Edition and All Things Considered. She's also a contributor to the PBS NewsHour and is one of the hosts of NPR's Life Kit.