Here is an experience: sit alone in a hospital room for two weeks and eat only ultra-processed foods such as hot dogs, muffins, canned ravioli and chicken salad.
You probably would not like the results.
But that's exactly what 20 men and women have done in a recent study rigorously controlled by the National Institutes of Health. These participants ended up earning an average of 2 pounds in those two weeks with this ultra-processed diet. They also consumed about 500 extra calories each day, compared to a different two-week period during which the same people followed an unprocessed meal plan.
The scientists behind the study – published on Thursday – found that this difference was due to the fact that patients fed on processed meals tended to eat too much, even as researchers controlled the amount of salt, fat, sugar, protein, fiber and carbohydrate in each meal (both treated and untreated).
"This is the first time we can really say that there is a cause-and-effect relationship between something that is independent of the nutrients … that is at the root of these differences in calorie intake and weight gain" said senior researcher Kevin Hall at Business Insider.
His team does not yet know why processed foods make us hungry, but they have some bright assumptions. On the one hand, they think that the difference in calorie consumption could have something to do with how fresh foods trigger hormones that regulate our appetite (ghrelin) and suppress hunger (PYY). In addition, people tend to eat unprocessed foods more slowly, giving our body more time to record that we are full before eating too much.
Previous research suggests that beyond eating too much, a diet that is high in processed foods is also linked to many other health problems: people who consume them regularly are more likely to get cancer and die faster than others.
Given this striking comparison, here's how to determine what to look for and what to avoid.
The difference between processed and unprocessed foods
Researchers classify "ultra-processed" foods as items that are typically manufactured in the factory and loaded with additives and preservatives such as sweeteners and thickeners. Generally, these things are packed in plastic or cans. It is likely that "high fructose corn syrup" is on the ingredient list of an ultra-processed food, or perhaps interesterified oils (trans fatty acid substitutes, now widely banned).
Unprocessed foods, on the other hand, contain raw materials such as fresh produce, unflavored yogurt, home-cooked meat and whole grains.
But foods do not have to be completely fresh to be considered unprocessed. In the NIH study, researchers used the NOVA food assessment system, which refers to foods as unprocessed if they are edible parts of plants (including nuts), animals, mushrooms, algae or water. It is therefore good to freeze, boil, ferment or refrigerate the ingredients. But unlike their processed versions, unprocessed foods are neither dried nor pre-salted.
The authors of the study described and photographed the meals they prepared with their 20 participants, both during their week of processed foods and the time spent on a fresher diet.
Here is one of the processed breakfasts that the participants ate in the lab:
One of the dishes prepared for lunch consisted of a delicious quesadilla based on turkey, cheddar and cinnamon cheeses, as well as fresh canned beans. Personally, I found it disheartening because it sounds like something I could do at home. The same was true for a canned chicken chicken salad sandwich, pickle relish and mayonnaise – one of the ultra-processed dinners.
On the other hand, while they were following a non-transformed diet, participants ate more products and jumped like tater tots. Here was what a day of unprocessed meals in the lab looked like:
Unprocessed breakfast: a yogurt parfait
Unprocessed lunch: spinach salad
Unprocessed dinner: roast beef tender stir fry
After two weeks of meal like this, the participants managed to lose an average of 2 pounds.