Randomized, Controlled Trial: Processed Food Leads to Massive Overeating

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We tend to avoid covering nutrition studies at RealClearScience, because frankly, most of them are utter crap. Every so often, however, a study gets published that bucks the broad trend of BS. Kevin Hall, a section chief in the Laboratory of Biological Modeling at the National Institutes of Health (NIH), along with numerous colleagues at the NIH, today published a study that deserves recognition. Their randomized, controlled trial demonstrates that people eating a diet of highly processed food consume far more calories than people eating a diet of unprocessed food. This may sound like an obvious result, one that any dietician could have predicted. But what sets this finding apart is the severity of the overeating and the sound methods used to discover it.

For their experiment, published to the journal Cell Metabolism, Hall and his co-authors recruited ten men and ten women to reside in a laboratory-controlled environment at the Metabolic Clinical Research Unit (MCRU) at the NIH Clinical Center. There, they dwelled for 28 days, watching TV, reading, occasionally exercising, and – most importantly – eating. Each subject was randomly assigned to two weeks of either a diet of highly processed food or unprocessed food, then each subject switched to the other diet for two weeks. They were all given three meals a day as well as snacks they could graze on whenever they chose. The processed menu featured meals like beef ravioli, sausage and eggs, and chicken tenders with macaroni and cheese, with snacks of chips, nuts, and goldfish crackers, while the unprocessed menu featured stir fries, oatmeal, and fresh pasta dishes, with snacks of various fruits and nuts. Crucially, both the processed and unprocessed diets were matched for presented calories, sugar, fat, sodium, fiber, and macronutrients. Subjects could eat "ad libitum," as much or as little as they desired.

When subjects were on the processed diets, they consumed 508 more calories per day, resulting in an average weight gain of two pounds over two weeks. Despite the fact that the diets were matched on a variety of characteristics, something about the highly processed foods caused subjects to eat a whole lot more.

"I was surprised by the findings from this study, because I thought that if we matched the two diets for components like sugars, fat, carbohydrates, protein, and sodium, there wouldn't be anything magical about the ultra-processed food that would cause people to eat more," lead author Kevin Hall said in a statement.

So what is it about processed foods that led to so much more eating in the study? The researchers noticed that when subjects were on the processed food diet, they ate a lot faster, perhaps giving their guts less time to relay feelings of satiety to the brain. Also noticeable was that processed foods were far more energy dense – while the meals were smaller in absolute size, they still contained the same amount of calories. The researchers also found that levels of an appetite-suppressing hormone increased on the unprocessed diet while levels of the hunger hormone ghrelin decreased.

Whatever the reasons, it's clear that consuming processed foods leads to higher calorie consumption. This is the first well-controlled trial in humans to evince this oft-spoken opinion.

"Our data suggest that eliminating ultra-processed foods from the diet decreases energy intake and results in weight loss, whereas a diet with a large proportion of ultra-processed food increases energy intake and leads to weight gain," the researchers conclude.

Source: Hall et al., "Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake," Cell Metabolism (2019), https://doi.org/10.1016/j.cmet.2019.05.008

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