- Processed foods have long been linked to shorter life spans and increased cancer cases.
- Groundbreaking research from the US’s National Institutes of Health suggests for the first time that the relationship is causal: No matter how nutritious they are, processed foods lead people to eat more and gain weight.
- Scientists still aren’t sure why this is the case, but they think there may be something unique about the way our hormones interact with processed foods. Plus, we typically eat them faster than unprocessed meals, meaning the body has less time to stop and register when it’s full.
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Too much sugar, too much salt, and too much fat.
We’ve been told for years that these are the culprits responsible for soaring obesity rates and expanding waistlines.
But groundbreaking research performed at a state-of-the-art nutrition lab in Maryland found that the nutritional value of what we eat may not matter nearly as much as how fresh our food is in the first place.
Nutrition experts at the National Institutes of Health have some of the first evidence, published Thursday in the journal Cell Metabolism, that there is something inherently bad about the way our bodies take in processed, ready-to-eat and ready-to-heat foods and that it makes us eat substantially more every day and get fatter over time than we would if we were eating fresh, home-cooked meals more regularly.
“I was surprised that we actually saw a very large effect,” the lead researcher, Kevin Hall, told Business Insider.
Researchers turned people into lab rats to better study their eating behaviors
For the study, Hall did something unusual: He put human participants into a hypercontrolled laboratory setting, where they ate all their meals in isolation for 28 days under strict medical observation. All the while, scientists measured changes in the participants’ insulin sensitivity, appetite, glucose, and a host of other metabolic and physical factors.
Researchers at the Bethesda Metabolic Clinical Research Unit enrolled 10 men and 10 women in the study, feeding them both ultra-processed and fresh diets in two-week increments.
Some participants used their lab time to study for board exams, while others played video games, Hall said.
“People often think of this as a way to kind of take time away from the day-to-day stresses of everyday life and focus on something, and have all their meals prepared for them,” he said.
The participants’ diets were precisely matched so that regardless of whether they were offered processed or unprocessed meals, they were given exactly the same amount of protein, fat, carbs, salt, and sugar to eat. They were instructed to eat as much food as they liked in 60-minute meal windows. They spent two weeks eating a processed diet, then switched and did two more weeks eating fresh meals.
Something remarkable happened, and it wasn’t at all what the researchers expected.
People who ate processed foods consumed about 500 more calories a day
Participants consumed, on average, 500 more calories a day on the ultra-processed diet, when meals included foods like hot dogs, freezer pancakes, canned chili, and peanut-butter-and-jelly sandwiches. Those eating processed foods also gained about two pounds in those two weeks. Regardless of the person’s weight or sex, they ate more carbs and fat on a processed-food diet.
“It’s a very big difference, and it’s an important difference,” Hall said. “There really is a causal relationship between ultra-processed foods and how many calories people choose to eat.”
The finding goes along with what long-term studies in free-roaming humans at home have suggested: Eating more processed and packaged foods is not good for us, increasing a person’s odds of dying or developing all kinds of cancers.
The difference between processed and unprocessed meals is subtle on the surface; both diet groups ate cereals, eggs, beans, and pastas. However, in the unprocessed group, the ingredients were fresher, with no additives or preservatives in the meals. Additionally, whole foods and unrefined ingredients were used (eggs and potatoes were prepared from scratch, for example).
If participants eating unprocessed meals ate black beans, they were cooked from dried beans, not popped out of a can like in the ultra-processed meals. The unprocessed breakfasts included yogurt, nuts, and plenty of fresh fruit. Lunch might be a spinach salad tossed with chicken breast, apples, and bulgur, topped with sunflower seeds.
This is not to say that everything on the unprocessed menu was made from scratch. Quinoa breakfast cereal was on offer, and frozen berries and corn were allowed.
Scientists still aren’t sure why people were tempted to eat more on the ultra-processed diet plans, especially because they tended to rate the tastiness of the processed and unprocessed food about the same. But they think there may be something about the way unprocessed, whole foods interact with hormones that helps us suppress our appetites and pay better attention to natural cues that we’re full.
Another possibility is that we tend to eat processed foods faster, so our bodies don’t have time to register when we’re full until we’ve overeaten.
“The point is that our paper doesn’t answer that question,” Hall said.
There is something to be said for the sheer convenience of prepackaged foods. Hall, a father of chicken-nugget-eating toddlers himself, understands the what-to-eat conundrum well.
“One has to be cognizant of the fact that people are living their day-to-day lives,” he said. “Ultra-processed food has a lot of advantages in terms of its convenience. It’s cheap. It sticks around for a while. You don’t have to have all the fresh ingredients on hand, which might spoil. You don’t have to have all the equipment to prepare these meals from scratch.”
Still, he said that trying to cut back on processed foods is a good idea, especially if you’re trying to manage your weight.
That strategy isn’t cheap, however. Ultra-processed meals in this study were priced at about $106 per week, while the unprocessed options were $151.