What Ultra-Processed Foods Do to the Body: The NOVA Classification and the Research

Not all processed food is the same. That distinction is the starting point for understanding the NOVA classification and the research built around it.

Bread is processed. So is a frozen dinner made with thirty-seven ingredients. Treating them the same, as most nutrition research did for decades, may have obscured a real signal in the data.

The NOVA Classification: What It Measures

NOVA was developed by Carlos Monteiro and colleagues at the University of São Paulo and organizes foods into four groups (Monteiro et al., 2019, Public Health Nutrition):

Group 1 includes minimally processed foods: fresh, dried, frozen, or fermented foods that have had nothing substantial added. Vegetables, fruits, plain meat, eggs, and plain milk fall here.

Group 2 covers processed culinary ingredients: substances extracted from whole foods and used in cooking. Oils, flours, salt, sugar, and butter are examples.

Group 3 is processed foods: whole foods with added Group 2 ingredients for preservation or taste. Canned beans, cheese, salted nuts, cured meats, and most whole grain breads are here.

Group 4 is ultra-processed foods: industrial formulations that contain little or no whole food and include multiple additives not typically used in home cooking. Packaged snack foods, carbonated soft drinks, mass-produced baked goods, flavored breakfast cereals, reconstituted meat products, and instant noodles are common examples.

The key distinction from nutrient-based classification is that NOVA measures what was done to the food, not just what’s in it. A chicken breast and a chicken nugget have similar protein content. NOVA correctly identifies them as very different food products.

The Hall 2019 Trial: Why It Matters

Observational studies had linked ultra-processed food intake to obesity, cardiovascular disease, and type 2 diabetes for years. Observational data can’t prove causation. People who eat a lot of ultra-processed food often differ in many other ways from people who don’t.

Hall et al. (2019, Cell Metabolism) ran a rare randomized controlled trial to test whether ultra-processed food causes overconsumption. Twenty adults were admitted to an inpatient NIH facility for four weeks. For two weeks they received ultra-processed meals; for two weeks they received unprocessed meals. Both diets were matched for offered calories, sugar, fat, fiber, and macronutrients. Participants could eat as much or as little as they wanted.

The result was stark. On the ultra-processed diet, participants ate about 500 more calories per day than on the unprocessed diet. They gained on average 0.9kg of body weight. On the unprocessed diet, they lost 0.9kg. Participants reported similar hunger and fullness ratings between the two diets, meaning the overconsumption wasn’t driven by feeling hungrier. Something else was causing them to eat more.

What the Mechanism Might Be

Hall and colleagues analyzed eating rate as a potential driver. Participants ate ultra-processed foods faster, consuming more calories per minute. Ultra-processed foods tend to require less chewing (softer textures), have higher palatability (more engineered flavor), and don’t require the same mechanical breakdown as whole foods.

Speed matters because satiety signals from gut hormones (GLP-1, PYY, CCK) take time to reach the brain. Eating faster outpaces those signals. You can consume significantly more food before the “stop eating” message arrives.

Fiber displacement is another factor. Ultra-processed foods are generally lower in fiber than unprocessed equivalents. Fiber increases gut transit time, slows glucose absorption, and feeds bacteria that produce appetite-suppressing short-chain fatty acids. A fiber-poor diet removes these brakes on intake.

Some researchers point to food additives including emulsifiers (polysorbate 80, carboxymethylcellulose) as potential contributors via gut microbiome disruption. Animal studies show certain emulsifiers alter microbiome composition and increase inflammatory signaling. Human evidence is more limited.

The Observational Data

A 2024 umbrella review by Lane et al. (BMJ) synthesized 45 systematic reviews and meta-analyses covering nearly 10 million people. Higher ultra-processed food intake was associated with increased risk of all-cause mortality, cardiovascular disease, type 2 diabetes, depression, and several other outcomes. The associations held even after adjusting for diet quality measures and other confounders.

These associations are consistent and large. They’re also observational, meaning confounding factors can never be fully ruled out. Ultra-processed food intake correlates with socioeconomic status, stress, sleep, and other factors that independently affect health.

The Hall 2019 trial matters because it provides randomized evidence that the food itself, not just who eats it, drives the effect. That combination of consistent observational data and a mechanistically plausible randomized trial makes the case against heavy ultra-processed food consumption reasonably strong, even if the precise mechanisms aren’t fully worked out.

Processing and Nutrients: Why They Aren’t the Same

The deepest insight from this research area is that processing level and nutritional content are different variables that don’t always move together.

Ultra-processed foods are often designed to hit specific macronutrient targets. They can be enriched with vitamins, fiber added back in, and fat reduced. Yet the Hall trial showed that nutritional matching didn’t equalize the eating response.

This suggests that the food matrix (the physical structure, texture, and composition of food as eaten) matters beyond macronutrient ratios. A nutrient-dense shake and a nutrient-matched whole-food meal affect eating behavior differently. This is an uncomfortable finding for nutrition science, which has long worked primarily at the level of macronutrients and micronutrients.

This article is for educational purposes only. It’s not medical advice. Talk to your doctor or a registered dietitian before making significant changes to your diet.