How to Tell the Difference Between Processed and Ultra-Processed Foods

Nutrition research is messy. The work on ultra-processed foods tidies things up.

A few years ago, I interviewed a Harvard professor of nutrition named David Ludwig.

Dr. Ludwig is a bestselling author and one of the leading voices in the nutritional sciences community. His writings and work have helped overhaul the way many Americans eat — mostly through his evidence-based defense of healthy dietary fats. If you’re eating more avocados, nuts, olive oil, and full-fat dairy than you used to, you probably have Ludwig to thank for it.

During that interview, Ludwig described many of the flaws that plague nutritional research — flaws that help explain why so many of us are confused about what and how to eat. Are fats healthy or unhealthy? What about carbs and cholesterol? Or gluten or sugar or dairy? “The public [is] dragged back and forth with every weak new research finding,” he told me.

He also said something that has stuck with me: “We know humans aren’t programmed to gain more weight generation after generation. Something has changed in our environment, driving even highly disciplined people to gain weight. We have to understand what that’s about.”

‘For the average adult, 60% of our diet is now ultra-processed. For kids, it’s 70%.’

Four years have passed since Ludwig and I spoke, and I think the picture of “what that’s about” has become much clearer. We are putting things in our bodies that are not supposed to be there, and that research has shown — with near-perfect consistency — to be strongly associated with obesity, chronic disease, and poor health. Those things are ultra-processed foods.

“You know, a lot of the research on nutrition just isn’t very good, but the evidence against ultra-processed foods is compelling,” says Dawn Harris Sherling, MD, a Florida-based physician and former instructor of medicine at Harvard University. “We know that these emulsifiers and thickeners and other additives are linked to myriad diseases, and we’ve shown in animal models how they can induce disease states.”

To her point, research in Nature Reviews: Endocrinology has shown that common emulsifiers (additives that help foods retain their stability and consistency) cause low-grade inflammation, metabolic disorders, and increased body weight in mice. “Researchers have hypothesized that emulsifiers may be responsible for breaking down the lining of our gut, which can change the way our bodies respond to food,” Sherling says.

In a small, first-of-its-kind study published the journal Cell Metabolism, researchers at the National Institutes of Health had healthy, weight-stable participants eat nothing but ultra-processed foods for two weeks. For a second two-week period, the same participants ate only whole unprocessed foods. While people lost an average of two pounds on the unprocessed-foods diet, they gained an average of two pounds when eating ultra-processed foods.

These are just two examples plucked from a huge pile of work linking ultra-processed foods to obesity, Type 2 diabetes, irritable bowel syndrome, inflammatory bowel disease, and other non-communicable diseases — including even mental health disorders — that have become widespread in recent decades.

Unfortunately, most of us are eating more of these foods than ever before. “For the average adult, 60% of our diet is now ultra-processed,” Sherling says. “For kids, it’s 70%.”

Sherling is the author of a new book, Eat Everything, that explores the dangers of ultra-processed foods. She says she was motivated to explore this topic in part based on her own experience with irritable bowel syndrome. “I had a stomach of steel in my 20s — I could eat anything — but then in my late 30s things started to go haywire,” she says.

During that time, her meals were often followed by periods of stomach pain. Trips to the bathroom were frequent. “I was trying everything — the low-FODMAP diet, gluten free, dairy free,” she says. “Then we took a family trip to Italy one summer, and within 24 hours I felt better.”

At first she figured that the foods she was eating — mostly fresh pasta and bread and produce — couldn’t be the cause of her improvement. “I thought maybe I was less stressed, or walking more,” she says. But then she got back to the U.S., her gut problems returned, and all her attempts to de-stress or exercise more didn’t help. “Later on we went back to Italy, and within 24 hours everything was fine again,” she says. “I looked at the food I was eating and I thought, gosh, this is actually different.”

The difference, she says, is that while plenty of the things she was eating in Italy were processed foods, almost none of them were ultra-processed. To differentiate between the two, she refers to something called the NOVA food classification system — a system initially developed by Brazilian researchers that has been used in processed-food research for decades.

“The NOVA classification system breaks food into four categories,” she says. The first category is whole foods — meats, eggs, nuts, seeds, produce, etc. The second category encompasses traditionally processed culinary ingredients — butter, sugar, spices, etc. — while the third includes traditionally processed foods like bread, pasta, and yogurt. Basically, these are processed foods or ingredients you would have found people eating hundreds or even thousands of years ago.

“Category 4 is all the new foods — the ultra-processed foods — that use more modern techniques and modern additives to preserve foods longer,” Sherling says.

‘I go to farmers markets and ask the baker if I can see an ingredients list, and there are all these additives.’

When the NOVA system was first introduced, its creators posited that it was a food’s level of processing — not its nutrient content — that might be most relevant when predicting its effect on human health, and Sherling says this argument has only grown stronger as the research has piled up. “Now that we have a better understanding of the microbiome and its role, we see how these ultra-processed foods are causing all kinds of problems and pro-inflammatory effects,” she says.

The work on ultra-processed foods also clears up a lot of the messiness and inconsistency that plagues nutrition studies that focus on macronutrients — on different types of carbs or fats or proteins — without attending to additives or processing. If you’re not controlling for ultra-processed foods, it makes sense that your results would be wildly inconsistent. As the food scientist Robert Lustig has told me, if we all just ate “real foods” and avoided ultra-processed ones, none of us would have to worry about dieting ever again.

Of course, avoiding ultra-processed foods is easier said than done. “It’s really challenging in the U.S. because everything nowadays is ultra-processed,” Sherling says. “I go to farmers markets and ask the baker if I can see an ingredients list, and there are all these additives.”

If you have the time (and money and dedication) to make most of your own foods from whole ingredients, that’s great. Do it.

But Sherling says another option is to be diligent about checking ingredients on any packaged foods that you buy. “You know, bread should be basically flour, water, salt, and yeast,” she says. If you see fifteen other ingredients and you don’t know what half of them are, that’s a sure sign you’re holding an ultra-processed food.

The same goes for yogurts, alternative milks, snack foods, pasta sauces, and anything else you buy in a package. “I can tell you it’s still possible to find things that are not ultra-processed in the supermarket — and I’m talking about the regular supermarket, not fancy natural markets — but you have to look,” she says.

“And listen,” she adds, “I’m not a purist and this is not a religion. If you love Cheez-Its and it’s not a major staple in your diet, go for it. If the average person could cut their processed food consumption from 60% down to five or 10%, that would be a huge improvement.”