A man on a quest to find the best diet tried eating only ultra-processed foods for a month. He quit after five days.

• Gavin Wren, a food-policy expert, challenges himself to eat a different diet every month.
• He tried eating only ultra-processed foods but gave up after five days.
• He said the diet made him feel sluggish and gave him a low mood.

A food-policy expert who challenged himself to eat only ultra-processed foods for a month as part of an experiment gave up after just five days.

Gavin Wren, a TikToker from the UK who shares insights about food policy, is on a quest to find the best diet for him; one that makes him feel good, allows him to socialize, and is good value for money. He has tried following popular diets, including veganism, the paleo diet, the Mediterranean diet, and only ultra-processed foods, for a whole month each.

He told Business Insider that the vegan and Mediterranean diets were his favorite but that the all-UPF diet was the worst.

Many people eat UPFs every day . A 2023 study published in The BMJ found that UPFs made up almost 60% of people's diets in the UK and the US. And a 2023 study published in Nature Communications found that 73% of the US food supply was ultra-processed.

While it's hard to avoid UPFs because they're so ubiquitous, experts advise people to cut down as much as possible. This is because UPFs are linked to health issues , such as type 2 diabetes, cardiovascular disease, cancers, and mental-health issues.

It's easy to eat too many ultra-processed foods

Wren typically eats a mostly whole-food diet and cooks all his meals from scratch. At first, it was "great fun" to indulge in foods he wouldn't typically eat, such as chips, fast food, and cake, he said.

But in the first few days of the experiment, Wren said, he found himself eating "an excessive amount" of calories and "sky high" levels of fat and sugar.

"A tube of Pringles is just addictive," he said. "So I'd just eat half of it, put it on the side, say, 'Right, I'll leave that for another time,' and then half an hour later I'm there finishing the tube."

A scientist previously told BI how UPF companies make their food irresistible .

Wren's experience of eating more on the UPF diet chimes with the results of a 2019 study published in the journal Cell Metabolism, which found that people ate about 500 kilocalories more a day when eating only UPFs versus whole foods. The researchers also matched the calories, energy density, macronutrients, fiber, sugars, and sodium of the processed and whole-food meals participants ate but found that the UPFs still had more added sugar and saturated fats.

Kevin Hall, the lead author of the study, previously told BI how his team was trying to figure out exactly why UPFs make people overeat .

His mood, energy, and mental health went 'down and down and down'

On day three of the diet, Wren woke up feeling something "akin to a hangover," he said, even though he hadn't drunk any alcohol. His energy was low, he felt sluggish, and he "didn't feel very good" in himself, he said.

"After a few days, my mood, my energy, and my mental health were just going down and down and down, and it was a real struggle," Wren said.

His experiences reflect the findings of a 2021 study published in BMJ Nutrition, Prevention & Health that found strong links between eating more fruits and vegetables and better mental well-being. And a 2019 study by researchers at the University of Paris suggested that the more UPFs people ate, the higher their risk of depression.

Work and going to the gym became harder

"My brain was really struggling to do normal things," Wren said, meaning his work really suffered on the UPF diet. There isn't much research into eating UPFs and concentration, but a 2022 study published in JAMA Neurology found a correlation between consuming more UPFs and having worse brain function and a faster rate of cognitive decline in a six-to-10-year period.

Wren also struggled to do his usual workouts at the gym. "I went to the gym, and I was just dead, just like no energy or anything. I felt terrible," he said.

He said he was "struggling to operate normally," so he quit the UPF diet. Wren quickly realized that an all-ultra-processed diet was definitely not for him.