Science

First-of-its-kind trial finds processed food causes overeating, but researchers not sure why

First-of-its-kind trial finds ...
This image shows one of the study's unprocessed lunches, consisting of a spinach salad with chicken breast, apple slices, bulgur, and sunflower seeds and grapes
This image shows one of the study's unprocessed lunches, consisting of a spinach salad with chicken breast, apple slices, bulgur, and sunflower seeds and grapes
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This image shows one of the study's processed lunches, consisting of quesadillas, refried beans, and diet lemonade
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This image shows one of the study's processed lunches, consisting of quesadillas, refried beans, and diet lemonade
This image shows one of the study's unprocessed lunches, consisting of a spinach salad with chicken breast, apple slices, bulgur, and sunflower seeds and grapes
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This image shows one of the study's unprocessed lunches, consisting of a spinach salad with chicken breast, apple slices, bulgur, and sunflower seeds and grapes

In a fascinating first-of-its-kind study, researchers have discovered diets composed of ultra-processed foods lead to overeating and weight gain when compared to diets composed of unprocessed foods. Both diets contained the same amounts of nutrients such as sugars and fats, leading to a hypothesis that something else in the ultra-processed food engenders overeating and weight gain.

The experiment took 20 healthy adults and administered them one of two specifically controlled meal plans. For two weeks the subjects ate either a diet consisting of unprocessed foods such as fruits, vegetables and nuts, or a diet of ultra-processed foods such as bread, sausages and baked goods. Importantly both diets were matched for calories, energy density, macronutrients, sugar, sodium, and fiber. The subjects were directed to eat as much as they felt they wanted.

"I was surprised by the findings from this study," explains Kevin Hall, lead author on the new 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. But we found that, in fact, people ate many more calories on the ultra-processed diet, and this caused them to gain weight and body fat."

After two weeks on the diets, the ultra-processed group had gained around two pounds of body weight and ate on average 500 calories more every day compared to the unprocessed group. It has previously been assumed that the high sugar, fat and salt content in processed foods is what drives a person to overeat and subsequently gain weight, but this study offers an interesting counterpoint to that hypothesis. The implication of the study is that there is some other unexplained mechanism at play causing a person to eat more when consuming ultra-processed foods.

This image shows one of the study's processed lunches, consisting of quesadillas, refried beans, and diet lemonade
This image shows one of the study's processed lunches, consisting of quesadillas, refried beans, and diet lemonade

"There may be something about the textural or sensory properties of the food that made them eat more quickly," hypothesizes Hall. "If you're eating very quickly, perhaps you're not giving your gastrointestinal tract enough time to signal to your brain that you're full. When this happens, you might easily overeat."

Blood measurements from each group revealed another intriguing datapoint. In those subjects eating the unprocessed diet increased levels of a hormone called PYY were detected. This hormone is known to act as an appetite suppressant. The unprocessed diet also resulted in decreases in ghrelin, a satiety hormone.

Perhaps the biggest limitation of the study comes in its somewhat arbitrary distinction between unprocessed foods and ultra-processed foods. Gunter Kuhnle, a nutrition expert from the University of Reading, suggests while the study is interesting and well-designed, it is difficult to find much meaning in the results due to the vague distinction between the two food categories.

"'Processed food' has become a catch-all phrase to describe 'unhealthy' food, when most foods are processed – and processing is usually important for palatability, safety and preservation," says Kuhnle, who did not work on this new study. "According to the NOVA classification, which has been used by the authors to categorize foods, chilling, freezing or packaging is already a processing step – and for example butter, cheese or bread are processed foods. The 'ultraprocessed' category is somewhat arbitrary, as it categorizes foods not by the actual processing steps used, but rather the intended outcomes of these processes."

The researchers behind this new study seem acutely aware of this limitation. Future work hopes to better home in on specific types of processed food and how they can possibly trigger overeating or body weight changes.

"We need to figure out what specific aspect of the ultra-processed foods affected people's eating behavior and led them to gain weight," says Hall. "The next step is to design similar studies with a reformulated ultra-processed diet to see if the changes can make the diet effect on calorie intake and body weight disappear."

The new research was published in the journal Cell Metabolism.

Source: National Institutes of Health / Cell Press via Eurekalert

14 comments
Muzza4
Anyone on a low carb diet knows exactly why this is.
Hankvana
What about the chewing and digestion process of the food? Is it possible that the less processed food takes more time to chew, literally more chewing effort, and hence individuals are satisfied with a lesser volume of food? Hank
rattus
Amazing - who would have thought a meal consisting of quesadillas, refried beans, sour cream, pizza, and 5 margaritas would have provided suboptimal nutrition? ;-)
rederje
A simple explanation is that all accustomed to eating ultra processed junk food since many years are quite less tempted by unprocessed good food so that they eat quite less what seems to them quite less pleasant !!
owlbeyou
While it is true that almost all food is processed, I do not consider the food I prepare (process) at home as such. At the end of the day, if you've been sensible enough not too eat too much of either foods, the processed variety is probably tastier, which may tempt one to eat more. There's also a whole lot of additives in P foods to make the eating experience seem better, as well as increasing the shelf life. The big food corps go out of their way to create new formulas for the public to (over)consume.
Daishi
I agree with the researcher that people are probably eating processed food faster. You are done eating before you realize you are full. Taking a break before 2nds and drinking water is a good strategy for this reason.
Kelly Ray
Duh, processed food just tastes better, so I'd expect the average person to eat more of it. You want 3 apples or 3 slices of pizza?
EZ
I read where there are over 80,000 additives that Big Fooda put in our food but only about 6 of them are regulated. I'll bet you'll never get any of our beloved food processors to admit to what they add to our food.
zephcom
Test the commercially processed food for chemicals which don't exist in the unprocessed food. Then test them to see if any added to the unprocessed food causes people to eat more and gain weight. I know, I know, it is inconceivable that Capitalists would add something to food which would make people buy more food. But if -I- were looking for the reason why this happens, it is where -I- would look first.
TOPDOG1
Big Foods ‘for greedy profit’ has killed more people with processed and counterfeit food items than both world wars and all worldwide terrorist attacks combined. Just Google ‘the Swiss milk study’ or the ‘Harvard milk study’, you will find that drinking more than three cups of PASTEURIZED milk has the mortality rate comparable to smoking three packs of cigarettes a day and with a hip-replacement thrown in. Even a cow would not drink that swill. All pasteurized foods and juices have been sterilized to prolong shelf life. This denatures the protein and destroys nearly all nutrition. You do not even want to know (but you should) what those nuggets are really made from. They no longer qualify as food. Everyone except an uneducated, near retarded and ignorant person knows what fried foods do. Drive-throughs are responsible for more deaths than drive by’s. If a terrorist wish to maim kill and hurt Americans all they need do is open a fast food restaurant. The F.D.A. may have started out as a competent research establishment but is now an obsolete deep state throwback to the cold-war era and should redirect their priorities away from politics and promoting the marijuana war and before they allow big foods to kill everyone off.