Why are Americans so sick? Researchers point to middle grocery aisles.

According to the Centers for Disease Control, more than 40 percent of Americans are obese, and many struggle with comorbidities such as Type 2 diabetes, heart disease, and cancer.

What is making us so sick? The ultra-processed foods that make up the bulk of the American diet are among the major culprits, according to an online panel hosted by Harvard’s T.H. Chan School of Public Health last week.

Experts from Harvard and the National Institutes of Health joined journalist Larissa Zimberoff, author of “Technically Food: Inside Silicon Valley’s Mission to Change What We Eat,” to discuss why the processing of cereals, breads, and other items typically found in the middle aisles of the grocery store — may be driving American weight gain.

Kevin Hall, senior investigator at the National Institute of Diabetes and Digestive and Kidney Diseases at the NIH, said initial research into diets high in ultra-processed foods shows strong links to overconsumption of calories.

Participants in a study conducted by Hall and his team published in 2019 were randomized to receive either ultra-processed or unprocessed diets for two weeks, immediately followed by the alternate diet for two weeks.

“But despite our diets being matched for various nutrients of concern, what we found was that people consuming the ultra-processed foods ate about 500 calories per day more over the two weeks that they were on that diet as compared to the minimally processed diet,” Hall said. “They gained weight and gained body fat. And when they were on the minimally processed diet, they spontaneously lost weight and lost body fat.”

According to Hall, “ultra-processed foods are one of the four categories of something called the NOVA classification system” developed by the School of Public Health at the University of São Paulo, Brazil.

Category 1 comprises minimally processed or unprocessed foods like fresh fruits and vegetables, poultry, and eggs. Category 2 includes “processed culinary ingredients” such as sugar or salt that you add to Category 1 foods to make dishes. Category 3 processed foods are a combination of Categories 1 and 2, such as canned beans or vegetables, cured meats, fresh bread, and cheeses. Category 4 ultra-processed foods are everything else: packaged snacks, frozen TV dinners, protein bars, pastries, and more.

Manufacturing techniques to create ultra-processed foods include extrusion, molding, and preprocessing by frying. Panelist Jerold Mande, CEO of Nourish Science and an adjunct professor of nutrition at the Chan School who has previously held positions with the FDA and USDA, pointed out that foods like shelf-stable breads found at the grocery store are often no more than “very sophisticated emulsified foams.”

But Hall noted that not all ultra-processed foods are necessarily equally bad for you. His team is conducting a follow-up study that aims to look at different qualities of ultra-processed versus whole foods, including energy density, palatability, and portions.

“Those are only two potential mechanisms, the calories per gram of food — that’s the energy density of food — and the proportion of foods that have pairs of nutrients that cross certain thresholds, foods that are high in both sugar and fat, salt and fat, and salt and carbohydrates,” he said.

“We’re starting to see a little bit of that evidence that some ultra-processed foods might have a higher risk of disease and chronic disease than others,” said Josiemer Mattei, the Donald and Sue Pritzker Associate Professor of Nutrition at the Chan School.

Still, Mattei argued for lowering consumption across the board.

“Higher consumption and higher intake of ultra-processed foods overall was associated with higher risk of eventually developing Type 2 diabetes, and more emerging evidence coming with cardiovascular disease, especially for coronary heart disease,” she said.

All the panelists agreed that obesity and negative health outcomes have risen alongside consumption of ultra-processed foods.

“We need to invest more in the science,” Mande said. “We need to make sure our regulatory agencies work, and we need to leverage the biggest programs.”