New findings published in the journal Cell Metabolism has found that eating highly processed foods for just two weeks can lead to weight gain and body fat increases regardless of sugar and fat contents.
“I was surprised by the results,” says lead author of the study Kevin Hall, senior investigator at the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health.
“It’s the first trial that can actually demonstrate that there is a causal relationship between something about ultra-processed foods—independent of those nutrients—that cause people to overeat and gain weight.”
Twenty healthy adults were recruited for the study. They all lived in a lab for a month with their meals and snacks prepared for them. For the first two weeks, volunteers were divided into two groups.
The first enjoyed a meal plan full of highly processed foods (think canned foods, fried nibbles and diet soft drinks) while the other ate only unprocessed foods (think fresh produce such as salads, nuts as well as eggs and oatmeal).
After the first two weeks, the groups switched to eat the other diet.
Interestingly, both diets included the same amount of sugar, fat, sodium and fibre. However, the highly processed diet resulted in an extra 500 more calories a day. Participants gained up to two kilos during the two weeks they were on that diet. Meanwhile when they switched to the unprocessed diet, they lost that same amount of weight.
The team of authors suspect one reason for gaining weight on the unhealthy diet could be eating faster.
“Ultra-processed food tends to be softer, which makes it easier to chew and swallow,”continues Hall.
“One of the theories is that if you’re eating more quickly, you’re not giving your gut enough time to signal to your brain that you’ve had enough calories and that you’re full and to stop eating. By the time the brain gets that signal, it’s too late—you’ve already overeaten.”
It wasn't just the rig that changed. Hormones were also impact by the eating plans. The unprocessed diet increased the appetite-suppressing hormone PYYY while decreasing the hunger hormone ghrellin.
“Both of these hormonal changes that took place, for reasons we don’t fully understand, tend to support our observation,” adds Hall.
“(Eating fresh food) people spontaneously reduce their calorie intake, leading to weight loss and body fat loss, without them having to count calories or even intentionally do so.”
However, the study also found that unprocessed cost 40 per cent more than ultra-processed foods. This could explain why people resort to microwave meals.