There are several hypotheses about how UPFs harm the body, though there’s still no consensus about the exact mechanism that causes the damage. Still, the research is moving quickly, says Schmidt. “Finding . . . [that mechanism] is the holy grail of nutrition science right now.” These are some of those theories.
1) Calorie Density
In 2019, a study correlated UPFs and weight gain for the first time. The randomized controlled trial, conducted by the National Institutes of Health, divided 20 healthy adults into two groups. For two weeks, one group ate only ultraprocessed foods while the other ate foods that were minimally processed. Then the groups switched diets and continued for two more weeks.
To increase the study’s accuracy, participants lived at the research center. Their meals contained an identical number of calories and grams of sugar, fat, sodium, fiber, and macronutrients. At mealtimes, both groups had an hour to eat as much or as little as they chose.
Researchers found that the subjects who were eating the UPFs consumed about 500 calories more per day than those eating minimally processed foods. After two weeks, members of the UPF group had gained an average of about 2 pounds.
By the end, researchers found that the subjects who were eating the UPFs consumed about 500 calories more per day than those eating minimally processed foods. After two weeks, members of the UPF group had gained an average of about 2 pounds.
2) Speed of Digestion
The body perceives industrially processed foods as essentially prechewed and predigested. That perception produces a host of repercussions along the digestive tract, starting in the mouth. Studies have shown that the longer a food must be chewed before it’s swallowed, the more satisfying it is to eat and the fuller a person feels afterward.
Research has also shown that people who chew their food longer consume fewer calories. In the NIH study, participants eating the ultraprocessed diet swallowed more calories per minute than did their counterparts. The combined eating speed and caloric density is what led to the extra 500 calories a day.
When we eat whole foods, the foods’ cells don’t break down completely, explains Juul. She compares whole almonds and almond flour: Whole almonds involve some serious chewing. After you swallow, your body absorbs only about 75 percent of their calories, she says, because the nut’s structure is still partly intact.
Once almonds are turned into almond flour, a higher percentage of their calories is absorbed into the bloodstream. This speed of absorption affects everything from blood-sugar levels to satiety hormones.
Evidence has suggested that highly palatable foods can dampen the body’s satiety signals, which can lead to overeating. As van Tulleken writes, “The signals that tell you to stop eating haven’t evolved to handle food this soft and easily digested.”
(After the gut, the mouth contains the most diverse microbial community in the body. As a result, the oral microbiome has a significant influence on your overall health. Learn more at “Everything You Need to Know About the Oral Microbiome.”)
3) Missing Nutrients
Studies suggest that UPFs are crowding out the nutrient-dense foods on our plates. In a 2021 meta-analysis, researchers noted a correlation between the increasing number of UPFs in meals and decreasing amounts of dietary fiber, protein, potassium, zinc, niacin, and vitamins A, C, D, E, and B12.
4) Novel Molecules
On a cellular level, nutrients exist in a certain structure within a food, and synergies exist between different nutrients and non-nutrients, says Juul. This is known as the food matrix, and it’s destroyed by industrial processing.
Our digestive system is designed to slowly and methodically break down a food’s matrix to glean the greatest nourishment for the body — and specifically for the microbiome.
Likewise, our signaling pathways evolved over millions of years to distinguish good molecules from bad. A molecule that is a shade different from one found in food can cause real problems with human chemistry, says Robert Rountree, MD, a Boulder, Colo.-based integrative family medicine practitioner. “Xenobiotic molecules gum up the works.”
5) Inflamed Gut
New evidence suggests that food additives, such as emulsifiers, thickeners, and artificial sweeteners, may cause gut inflammation. This can lead to a variety of gastrointestinal issues, including IBS.
Presently, more than 60 types of emulsifiers are used in UPFs, including polysorbate 80, carboxymethylcellulose, and carrageenan. Studies have found that mice exposed to these substances developed gut inflammation after 12 weeks.
There’s also a potential cocktail effect from multiple food additives in a single UPF, as well as in the many combinations that might be eaten in a handful of foods at one sitting.
“All of us are subjects in a food experiment that humans have never encountered before,” says Devries. “As a result, we are seeing a greater spectrum of digestive problems than have ever been observed before.”
Ultraprocessed Foods are Everywhere
Take a closer look at the many ways these food products can harm your health — and why it’s worth the effort to avoid them when you can at “The Truth About Ultraprocessed Foods,” from which this article was excerpted.
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