healthHealth and Medicine

Here’s What Happens When You Eat Mostly Ultra-Processed Foods For A Month


Ben Taub

Freelance Writer

clockOct 5 2021, 15:04 UTC
Ultra-processed foods

Ultra-processed foods make up a significant proportion of many people's diets in developed countries. Image: beats1/

Recent surveys have indicated that children in some developed countries now receive two-thirds of their calories from ultra-processed foods, leading to concerns over a lack of research into the impact that such a diet can have on physiology. To fill this knowledge gap, British doctor Chris van Tulleken recently switched to a diet consisting of 80 percent ultra-processed foods for 30 days, resulting in an array of negative changes to his body and brain.

Filming his experiment as part of a BBC documentary called 'What Are We Feeding Our Kids?', Dr van Tulleken explained that while such excessive consumption of highly processed food might sound extreme, “it’s the same diet that one in five people in the UK eats.” Beginning with a breakfast of fried chicken containing an assortment of chemicals like monosodium glutamate, he spent an entire month stuffing his face with “hyper-palatable” food items, although while his tastebuds might have enjoyed the experiment, it wasn’t long before his body started to suffer.


Within just a few days, he noticed that he felt hungry more often than he used to, and even began to crave food. To make matters worse, Van Tulleken soon became constipated, documenting the fact by recording “a video of me not having a poo… but needing a poo.”

When the 30 days were up, he found that he had put on an incredible 6.5 kilograms (14.33 pounds) in weight, which included an additional three kilograms (6.6 pounds) of body fat. Based on this outcome, he calculates that maintaining this diet for six months would cause him to balloon by a whopping six stone (84 pounds).

Dr Van Tulleken’s body mass index also increased by two points over the month, pushing him into the overweight range, while a number of alarming hormone changes also occurred. For instance, blood tests revealed a 30 percent increase in “hunger hormones” that drive the desire to eat, while “fullness hormones” that tell the brain not to do so were lowered.

Perhaps the most striking and alarming changes, however, were seen in the brain. By comparing brain scans conducted before and after the experiment, doctors revealed that the diet had sparked the creation of new functional connections between certain brain regions.


“The diet has linked up the reward centres of my brain with the areas that drive repetitive, automatic behaviour,” explains Van Tulleken. “So eating ultra-processed food has become something my brain simply tells me to do without me even wanting it.”

“This is something you might see in a person with addiction.”

Ultra-processed foods are generally industrially produced and contain a high number of chemical ingredients. While it isn’t fully understood how these products generate these negative effects, a recent study revealed that people who eat mostly ultra-processed foods tend to consume 500 more calories per day than those who eat unprocessed foods – even when their diets were matched for salt, fat and sugar content.

Summing up the dangers of offering such an unnatural diet to youngsters, Vall Tulleken says that “my concern is that children’s brains are still developing and they’re much more malleable than mine, which means the changes are likely to be even greater.”

healthHealth and Medicine
  • tag
  • diet,

  • food,

  • processed food,

  • ultra-processed