I Ate Ultra-Processed Foods, My Twin Didn't. The Results Were Shocking

Before taking part in a study of the impact of ultra-processed foods (UPFs), I would say my diet was balanced. I love cooking, so I ate a lot of homemade food from whole, less processed groceries.

However, I didn't really make a conscious effort to avoid UPFs, and was probably more likely to choose a food based on the number of calories or labeling, rather than the ingredients list.

Earlier this year, Twins UK—a registry of twins available to contribute to scientific research— asked us if we would be interested in taking part in a test carried out by Professor Tim Spector from King's College London, which would see me eat only UPFs for two weeks.

My twin sister, Nancy, would consume the same number of calories, nutrients, fat, sugar, and fiber, but eat only non or low-processed foods.

We had both previously taken part in the ZOE Predict studies, analyzing how different people respond to food, and already knew Tim Spector. Plus my sister had been following his previous research on UPFs.

She'd read all of Professor Spector's books and was a weekly listener of the ZOE Science and Nutrition podcast, so she thought this was a really exciting opportunity. I obviously agreed. We are both keen on science and contributing where we can.

During the study, my typical breakfast was pancakes with syrup, hash brown and sausage, an instant flavored porridge with syrup and honey-roasted nuts, breakfast cereal with a blueberry muffin, or a flavored creamy yogurt and a croissant.

For lunch I ate either a peanut butter and jelly sandwich on white bread with chocolate milk and some chips, a turkey and mayo sandwich with chips and some packaged peaches, or ravioli with cheese and a cookie.

Dinner was meals like cheeseburger and chips, beef with mash gravy and tinned sweetcorn, a meatball sub with cheese and some crackers, or ready-made turkey quesadillas with sour cream, a Diet Coke, and a chocolate bar.

There was very limited fresh food, and no fruits or vegetables. Everything was really easy to eat mindlessly; I didn't have to put any effort into eating it. It's the type of food I could eat quickly, and it would taste consistently good.

I felt the increase in hunger early on. Within the first meal or two, I felt a real urge to snack between meals. Changes to my mood took a bit longer, maybe about a week but then I was noticeably lower in mood.

The biggest change I noticed was being hungry all the time. Despite eating more calories than my typical diet pre-study, I was waking up really hungry in the morning and didn't find my meals satisfying.

I felt really tired. So much so that by the end of the two weeks, friends and family commented on how exhausted I looked.

I constantly felt like I had less energy and found it really hard to concentrate—especially at work in the afternoon as I was constantly thinking about food. Very sweet, refined carbohydrates made me feel worse.

At the end of the study, I was ready to go back to a more normal diet. It was exhausting to feel so hungry and tired all the time, even if only for two weeks.

More than anything, I was looking forward to cooking my own food again and choosing what I was going to be eating, as the meals had been prepared by a chef for us.

Whilst mentally I was looking forward to going back to my normal diet, I was surprised that my body was still craving UPFs.

The results of the study showed that in just two weeks, I had put on weight and my blood sugar and fat levels had worsened. Meanwhile, Nancy's results showed the opposite—she was slimmer and had better blood results.

Neither of us is overweight or unwell in any way, so I was shocked that as a young, healthy person, it affected my health in as little as two weeks.

During the study, my sister didn't really feel hungry and didn't feel the need to snack, which I definitely did. She actually felt full and sometimes didn't even manage to finish her meals. Her mood was also better than mine.

To a certain extent, it was difficult to wean myself off the ultra-processed diet. I didn't really enjoy the food, but finished everything I was given and was always left wanting more. I also liked the convenience of the food.

As a result of the study, my sister has tried new foods, like porridge made with quinoa rather than oats, which she noticed kept her fuller for longer.

This experience has definitely changed the way I approach food. I initially believed my diet was low on UPF, but actually, I was eating way more of them than I thought.

For example, fruity-flavored yogurts, sliced brown bread, and cereal bars marketed as "whole foods" but which contained emulsifiers, preservatives, and sweeteners.

Now, I'm making a conscious effort to eat more whole foods, especially when it comes to snacking.

I don't think it's sustainable, or even possible to cut them out completely, but I'm eating UPFs a lot more mindfully now—enjoying them when I fancy them, but aware of how they affect my body.

Aimee Kingston took part in King's College London's study for BBC One's Panorama on ultra-processed foods.

All views expressed in this article are the author's own.

As told to Newsweek's My Turn associate editor, Monica Greep.

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