Ultra-processed foods are killing us – but we don’t understand exactly how

 

Who remembers Morgan Spurlock? The documentary filmmaker consumed only McDonalds for a month and gained 11kg doing it. He released the film of that experiment in 2004 (Super Size Me).

Fifteen years later and the warnings about processed food have become more frequent. We’ve all seen and heard them for years. We all know that ultra-processing means fewer nutrients and more sugar, salt, saturated fat, and food additives. The problem is that ultra-processed foods have been cleverly marketed for decades and include the comfort foods, treats, easy meals and takeaways that have become a part of everyday life. The bicycle delivery guy that nearly ran you over wasn’t rushing a salad to some busy diet-conscious office worker.

An observational study published this year followed almost 45,000 adults over a two-year period. On average, ultra-processed foods made up about 15% of their daily diet. There was a direct statistical connection between higher intake of ultra-processed food and a higher risk of early death from all causes, especially cancers and cardiovascular disease.

So, that’s that then…….not quite. Another study published this year took an unusual approach. The study volunteers lived for 28 days at a metabolic study centre, which is part of the National Institutes of Health (NIH) in the USA. Each volunteer had one diet for the first two weeks (either ultra-processed or un-processed) and then swapped for the alternate diet for the next 2 weeks. The really interesting part of the study was that the diets were matched for presented calories, sugar, fat, fibre and macronutrients. The volunteers could eat as much as they liked during the study.

Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of  Ad Libitum  Food Intake https://doi.org/10.1016/j.cmet.2019.05.008

Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake https://doi.org/10.1016/j.cmet.2019.05.008

The changes were rapid and extraordinary.  Despite the ultra-processed and unprocessed diets being matched for daily presented calories, sugar, fat, fibre and macronutrients, people consumed more calories when exposed to the ultra-processed diet as compared to the unprocessed diet. Furthermore, people gained weight on the ultra-processed diet and lost weight on the unprocessed diet.

When the participants were eating the unprocessed diet, they had higher levels of an appetite-suppressing hormone and lower levels of a hunger hormone, which might explain why they ate fewer calories. On the ultra-processed diet, these hormonal changes flipped, so participants had lower levels of the appetite-suppressing hormone and higher levels of the hunger hormone.

In addition, people ate much faster — both in terms of grams per minute and calories per minute — on the ultra-processed diet.

The lead researcher, who ran the study, said it may be that, because the ultra-processed foods tended to be softer and easier to chew, people devoured them more quickly, so they didn't give their gastrointestinal tracts enough time to signal to their brains that they were full and ended up overeating.

A longer review of the study can be found here.