Everyone knows that too much “junk food” is bad for you — that’s why we call it junk food. Some classic snacks, desserts and fast food probably come to mind: the chips, cookies and french fries of the world. These foods are specially made to be delicious (some would say to the point of addiction) and have a long shelf life, which means they’re packed full of quick-digesting sugars and other carbs, and unhealthy fats.
But lately, scientists are veering from the phrase “junk food” — no need to judge people for their eating habits — and are instead focusing on more specific terms such as processed and ultra-processed foods.
Processed foods include anything that’s been cooked, canned, frozen or otherwise altered in any way – so, clearly, processing has been part of the human diet for centuries. And it’s not all unhealthy: Even staples like bread and cheese count as processed.
But ultra-processed foods are a more modern invention, and they’ve been seriously altered from their natural states. For a long time, people assumed these ultra-processed foods were unhealthy because some of their ingredients were unhealthy. And they often are. But recently, research has revealed that the heavy processing that goes into making these foods is itself a major component of why they’re so unhealthy.
What is an ultra-processed food?
What exactly makes a food “ultra-processed” varies according to the source, but there are a few key steps almost everyone agrees on. High degrees of processing rely on splitting once whole ingredients into their non-natural constituent parts, and frequently chemically modifying the resulting ingredients. You’ll also often find cosmetic additives like dyes in highly processed foods to make them look more palatable (Monteiro et al., 2019).
As a consumer, the biggest red flag that something has been highly processed is synthetic chemicals on the ingredient list you’d never find in any kitchen. This includes high fructose corn syrup, hydrogenated oils (or cheap seed oils such as one of the “Hateful 8”), emulsifiers, synthetic sweeteners, thickeners and other chemicals like foaming, gelling and glazing agents.
This suggests that more foods qualify as ultra-processed than you might think. Most pre-made boxed meals you buy at the supermarket are highly processed, for example, no matter whether they claim to be healthy or organic.
While things like freezing or canning are technically processing, researchers today make a distinction between that kind of packaging and far more invasive processes that pull apart food on the molecular level and add back in chemicals you’d never find in nature.
Some researchers have used the term “acellullar” to describe this extreme level of processing, An acellular food, viewed under a microscope, has been so thoroughly pulverized by heat, pressure, mechanical action or solvents that not a single cell from the source material remains intact and visible.
In other words, it has been ultra-processed.
Health effects of ultra-processed foods
In a 2019 study searching for links between how people ate and how healthy they were, researchers followed a cohort of almost 20,000 people from 1999 to 2014, to track their dietary habits (Rico-Campà et al., 2019). They found that eating more ultra-processed foods was associated with a higher risk of death by any cause. People who consumed more than four servings of ultra-processed foods daily increased their risk of death by 62 percent.
A similar study from 2018 with over 100,000 participants found that people who ate just 10 percent more ultra-processed foods had more than a 10 percent increase in their likelihood of developing cancer (Fiolet et al., 2018).
Another research team found that older adults who consumed more ultra-processed foods over the course of six years put on significantly more weight around their midsections, even when they started off slim (Sandoval-Insausti et al., 2020). The result held up even when the researchers controlled for dietary factors like fiber and omega-3s.
Some experts think the harmful effects of ultra-processed foods begin with our microbiomes, the collection of bacteria and other microbes living in our guts that help with digestion and much more (Zinöcker & Lindseth, 2018). Different microbes thrive on different foods, and these microbes in turn have different effects on our bodies. Eating too many foods that help the “bad” microbes thrive and not enough that feeds the “good” microbes can cause a harmful shift in the overall composition of what lives in our guts. Too many bad microbes can lead to widespread inflammation, which has been linked to a number of conditions, like cancer, heart disease, arthritis and diabetes.
Putting ultra-processed foods to the test
Researchers are starting to figure out why, exactly, these foods are so bad for us. In a landmark 2019 study, 20 young adults checked into a special research facility at the National Institutes of Health and stayed there for a month (Hall et al., 2019). There, researchers gave them a strictly regimented diet that allowed them to cut out many variables that plague studies using real-world subjects, and let the scientists isolate the effects of diet.
Each participant ate one of two experimental diets for the first two weeks, then switched to the other for the second half of their stay. For every meal, researchers provided a full spread — more than anyone would eat in a sitting — and participants were told to eat until they were full.
One diet was made exclusively of ultra-processed foods, and included things like refried bean quesadillas and chicken-salad sandwiches The second diet was unprocessed or lightly processed, and included oatmeal, salads and omelets. (Check out the diets here.)
But the key was that both sets of meal offerings were the same from a nutritional standpoint: Same calories, fat, protein, sugar, sodium, fiber, carbohydrates and even energy density (calories per weight of the food). The only difference was how processed the foods were. The researchers also made sure participants rated the meals similarly for “pleasantness” and “familiarity,” so the experiment wouldn’t be confused by participants eating less of the unprocessed foods because they didn’t like them as much.
They found that participants ate, on average, 500 more calories per day when presented with the ultra-processed foods, with most of that increase coming from carbohydrates and fat. In each two-week period, on average, participants gained more than two pounds on the ultra-processed diet, and lost more than two pounds on the unprocessed diet.
These results are striking, and they have an important message for everyone. demonstrating It’s not just the stats on the nutrition labels that are problematic for many ultra-processed foods. Something about the degree of processing itself makes a difference. Shifting the composition of these foods to be healthier, like by adding fiber and protein, won’t solve the underlying issue.
What’s for dinner?
If you’re already trying to eat healthy, you’re probably already focused on eating more whole, unprocessed foods. Just as fresh fruit is far healthier than juice from concentrate, a baked potato is healthier than a potato chip, and 100 percent whole-grain bread – preferably with chunks of intact and/or sprouted grain - is healthier than sweet white bread. Fiber from natural sources like grains and produce is better than, say, fiber supplements or a fiber-added granola bar. While different diets might recommend eating different proportions of grains, fruits, vegetables, seafood, meats and eggs, we can all agree that these whole, unprocessed foods are healthier for you than their processed counterparts.
Read more: Eat the Rainbow (and Here’s Why You Should)
The Bottom Line
Out with the ultra-processed foods, in with the whole foods! If you’re able, cooking at home is a great way to prioritize whole foods. Instead of focusing on foods to avoid, focus on foods to get more of, like fresh produce or a nice whole Alaskan sockeye fillet. Or focus on both with our “Sardines Simmered In Roasted Roma Tomatoes” recipe. When you’re eating out, choose dishes that are baked, steamed or sautéed instead of fried, and go for veggie-loaded sides.
And if the precise definition of ultra-processed food still sometimes escapes you (as it does many of us) remember the advice of famed food writer Michael Pollan: “Don’t eat anything your great, great grandmother wouldn’t recognize as food.”
Monteiro, C, Cannon, G., Levy, R, Moubarac, J., Louzada, M, Rauber, F, Jaime, P et al. (2019). Ultra-processed foods: What they are and how to identify them. Public Health Nutrition, 22(5), 936-941. doi:10.1017/S1368980018003762
Sandoval-Insausti H, Jiménez-Onsurbe M, Donat-Vargas C, Rey-García J, Banegas JR, Rodríguez-Artalejo F, Guallar-Castillón P. Ultra-Processed Food Consumption Is Associated with Abdominal Obesity: A Prospective Cohort Study in Older Adults. Nutrients. 2020; 12(8):2368. https://doi.org/10.3390/nu12082368
Zinöcker MK, Lindseth IA. The Western Diet-Microbiome-Host Interaction and Its Role in Metabolic Disease. Nutrients. 2018;10(3):365. Published 2018 Mar 17. doi:10.3390/nu10030365
Rico-Campà A, Martínez-González M A, Alvarez-Alvarez I, de Deus Mendonça R, de la Fuente-Arrillaga C, Gómez-Donoso C, Bes-Rastrollo M. Association between consumption of ultra-processed foods and all cause mortality: SUN prospective cohort study BMJ 2019 doi:10.1136/bmj.l1949
Fiolet T, Srour B, Sellem L, Kesse-Guyot E, Allès B, Méjean C, et al. Consumption of ultra-processed foods and cancer risk: results from NutriNet-Santé prospective cohort BMJ 2018; doi:10.1136/bmj.k322
Poti, JM, Braga B & Qin B. Ultra-processed Food Intake and Obesity: What Really Matters for Health—Processing or Nutrient Content? Curr Obes Rep 2017 6:420–431. https://doi.org/10.1007/s13679-017-0285-4
Hall KD, Ayuketah A, Brychta R, Cai H, Cassimatis T, Chen KY, Chung ST, Costa E, Courville A, Darcey V, Fletcher LA, Forde CG, Gharib AM, Guo J, Howard R, Joseph PV, et al, Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake, 2019, Cell Metabolism, 30(1)67-77.e3 https://doi.org/10.1016/j.cmet.2019.05.008.