Processed Foods Shown to Have “Surprising Effects” on the Body in New Study

"Studies such as ours are rare in nutrition science."

Cell Metabolism 

The phrase “ultra-processed foods” is unappetizing enough on its own, but new research on the health effects of these beloved foods makes them even less appealing. On Thursday, a paper published in Cell Metabolism makes one of the strongest cases yet against some fan favorites, from frozen mac and cheese to shelf-stable cookies and Honey Nut Cheerios. They seem to go down easier, causing us to unconsciously eat more than we need.

Lead study author Kevin Hall, Ph.D., a scientist with the National Institutes of Health, noticed that his 20 adult participants ate very differently when they were given daily diets of either processed or unprocessed foods for two weeks at a time. Specifically, people on a processed food-only diet ate about 508 extra calories at meal times, in particular at breakfast and lunch.

Hall tells Inverse that he was “surprised” by how many extra calories the ultra-processed group ate for two reasons. First, the participants didn’t indicate that the processed meals were any more pleasant or satisfying. Second, the meals were very closely matched for metrics like calorie count, salt content, fat, and sugar. But despite the similarities, people just couldn’t help themselves when faced with ultra-processed food.

“It suggests to me that something about the ultra-processed foods independent of these nutrients can also have a major effect on regulating appetite and body weight,” he says.

People who ate processed food diets gained more weight over two weeks than those who ate unprocessed food even though the caloric content of the meals was the same. Instead, the people on the unprocessed diets tended to snack more. 

Cell Metabolism 

What Is “Ultra-Processed Food,” Anyway?

Most things we eat are manipulated in some way, but that doesn’t necessarily mean that item is ultra-processed or even processed. According to the NOVA food guidelines, which are recognized by the United Nations and the Pan American Health Organization, a completely unprocessed food is just one ingredient (think a vegetable). Even minimally processed foods, like frozen fruit, are in the same category.

A processed food, in contrast, has about two or three ingredients altogether — usually oil, salt, or additives, like fruits in syrups. And an ultra-processed item typically has far more than five ingredients and contains some kind of additional enhancement, like a dye, flavor enhancer, carbonator, or non-sugar sweetener. Under this criteria, foods from soft drinks to fish sticks fit the bill.

Dinner in the processed food condition (left) compared to dinner in the unprocessed food condition (right).

Cell Metabolism 

In Hall’s study, a typical day’s meals in the ultra-processed condition might consist of a breakfast of Honey Nut Cheerios, a lunch of a quesadilla, and a dinner of tempura chicken nuggets. Compare that to the unprocessed condition, where participants had Greek yogurt, salads with chicken, or steak with broccoli and rice. Each participant got a chance to live the processed or unprocessed life for two weeks and then switched to the alternate diet for two more weeks.

Crucially, both of these diets were matched for caloric content, meaning that during any meal on any given day, participants in both groups were presented with dishes that had the same amount of calories. Despite not indicating that they liked the meals any more, the people on the ultra-processed diets ate more of the food in front of them — which is how they racked up the extra 508 calories.

Overall, this pattern led people on the processed food diet to gain about 2 lbs of body weight over the course of the study. Interestingly, they tended to lose that extra 2 lbs when they switched to the unprocessed diet.

A Reformulation Strategy?

The strength of his study is in its design. Hall really was able to show cause and effect and had full control to his participants eating habits because they lived in the NIH’s Metabolic Clinical Research Unit — a luxury not available to many nutritionists. “Studies such as ours are rare in nutrition science,” he says.

Now, he’s got to figure out what it is about processed food that makes people eat so much more of it.

“We first need to understand the mechanisms by which ultra-processed foods exert their effects,” he explains, noting that his new study will reformulate ultra-processed diets to see if they can be made less easy to eat and less likely to lead to weight gain.

"We first need to understand the mechanisms by which ultra-processed foods exert their effects.”

The current paper floats the idea, suggesting there could be a way to reformulate processed foods to get around their effects on snacking once they figure out what ingredients are causing them. This seems strange for a few reasons, namely because the larger takeaway seems to be that it’s worth avoiding processed foods.

But the paper points out that truly abandoning processed foods is hard for a few reasons.

For one, the unprocessed food diet was more expensive than the processed food diet by $45, which is indicative of larger issues with the affordability of healthy food. Processed foods, meanwhile, are “relatively cheap and tasty while being convenient to prepare.” In short, they’re crowd-pleasers that work for people who are already busy. And so a reformulation, in short of a lifestyle change or overhauls to the food system, could be a temporary workaround that may combat those effects.

Hall isn’t the first to take aim at the health effects of processed foods, but he is among the first to show a clear and causal connection and use it to show why they may be taking a toll on the nation’s well-being. Health-conscious as we may be becoming, when it comes to ultra-processed foods, it’s just easier to eat more of them — even if we’re not completely aware of it.

We investigated whether ultra-processed foods affect energy intake in 20 weight-stable adults, aged (mean ± SE) 31.2 ± 1.6 years and BMI = 27 ± 1.5 kg/m2. Subjects were admitted to the NIH Clinical Center and randomized to receive either ultra-pro- cessed or unprocessed diets for 2 weeks immedi- ately followed by the alternate diet for 2 weeks. Meals were designed to be matched for presented calories, energy density, macronutrients, sugar, sodium, and fiber. Subjects were instructed to consume as much or as little as desired. Energy intake was greater during the ultra-processed diet (508 ± 106 kcal/day; p = 0.0001), with increased consump- tion of carbohydrate (280 ± 54 kcal/day; p < 0.0001) and fat (230 ± 53 kcal/day; p = 0.0004), but not protein (2 ± 12 kcal/day; p = 0.85). Weight changes were highly correlated with energy intake (r = 0.8, p < 0.0001), with participants gaining 0.9 ± 0.3 kg (p = 0.009) during the ultra-processed diet and losing 0.9 ± 0.3 kg (p = 0.007) during the unprocessed diet. Limiting consumption of ultra-processed foods may be an effective strategy for obesity prevention and treatment.
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