The big question: process or ingredients?
Ultra-processed foods, or UPFs, now make up a huge share of what many people eat. Observational studies have linked high UPF intake to higher rates of cancer, cardiovascular disease, diabetes, and earlier death. But those studies cannot answer a basic question that matters for real life and policy.
Are UPFs harmful mainly because of the way they are manufactured and industrially processed, because of their nutrient profile, or because of both in different ways?
A new randomized controlled feeding trial is designed to tease those factors apart instead of treating all ultra-processed foods as one monolithic category.
How the trial is designed
Researchers have built a 2 × 2 factorial trial with two levers. One is how processed the diet is, using NOVA categories to define “high UPF” versus “low UPF.” The other is how “unhealthy” the nutrient profile is, focusing on saturated fat, added sugars, and sodium, often abbreviated as SFSS.
That creates four different diets:
- Low UPF, low in saturated fat, added sugar, and sodium.
- Low UPF, high in saturated fat, added sugar, and sodium.
- High UPF, low in saturated fat, added sugar, and sodium.
- High UPF, high in saturated fat, added sugar, and sodium.
Healthy adults aged 18 to 75 with a body mass index between 18 and 35, no diabetes, cancer, or cardiovascular disease, and relatively normal blood pressure, cholesterol, and blood sugar will be enrolled. People on blood pressure, cholesterol, or diabetes medications, heavy drinkers, pregnant or lactating women, and anyone with major food allergies, restrictive diets, or conditions that would make the diets unsafe or hard to follow are excluded.
Each participant will be randomly assigned to one of the four diets for six weeks.
What people actually eat in the study
This is not a loose “eat more or less junk” assignment. It is a fully controlled feeding trial.
Everyone gets the same total calories, about 2,500 per day. Protein, carbs, and fat are matched at roughly 15% protein, 50% carbohydrate, and 35% fat across all diets. The only deliberate differences are how processed the foods are and how high or low they are in saturated fat, added sugar, and sodium.
High UPF menus lean heavily on commercial ultra-processed products like flavored yogurts, packaged cookies, waffles, spaghetti with jarred sauce, and ready-to-eat coleslaw. Low UPF menus rely on minimally processed or simply processed ingredients and recipes, such as plain yogurt sweetened with maple syrup and fruit, spaghetti with homemade sauce, homemade cookies, and pancakes from scratch.
Participants eat supervised meals on some weekdays in a study cafeteria, then take home prepared foods and snacks to cover the rest of their days. They are asked to avoid alcohol, probiotics, natural health products, artificially sweetened drinks, and fiber supplements so those extras do not muddy the results. Daily checklists help monitor how closely they stick to the assigned diet.
What the researchers will measure
The main outcomes are classic cardiometabolic risk markers. These include LDL cholesterol, the “bad” cholesterol, daytime ambulatory systolic blood pressure, and insulin resistance, calculated using a standard measure called HOMA‑IR. These are checked at the start and again at the end of the six-week diet period.
Secondary measures include triglycerides, ApoB‑100, HDL cholesterol, around-the-clock blood pressure readings, and fasting glucose and insulin.
There is also a quality-of-life and experience layer. Participants complete questionnaires on how healthy they perceive the meals to be, how tasty they are, how hungry or full they feel, how much they enjoy eating the foods, and how active they are. Body composition scans at the beginning and end of the trial track total body fat and where that fat is stored.
All of this will be analyzed using models that keep participants in their original groups for analysis, even if adherence is not perfect, which is closer to how real life works.
What this trial could actually answer — and what it can’t
The trial is built around a strong hypothesis that the high saturated fat, added sugar, and sodium content of some ultra-processed foods drives most of the cardiometabolic risk and that the degree of industrial processing by itself matters less once those nutrients are matched.
Because of its design, the study has some real strengths. It can separate “how processed” a food is from “how much saturated fat, sugar, and salt it contains,” instead of treating those as one blob. Controlled feeding and matched calories eliminate a lot of confounding from weight loss or gain. The factorial design allows the team to test both main effects and interactions, for example, whether highly processed, high SFSS diets are worse than you would expect from either factor alone.
There are also important limits. Because calories are matched to maintain weight, this trial will not directly show whether ultra-processed diets cause people to overeat or gain weight when they can eat freely. The participants are relatively healthy adults, so the results may not translate directly to people with existing diabetes, heart disease, or obesity. The intervention lasts six weeks, which is enough to move lab markers but not long enough to see hard outcomes like heart attacks or diabetes diagnoses.
Still, the findings could matter a lot for public health guidelines. If nutrient profile turns out to be the main driver, policies might emphasize slashing added sugars, saturated fat, and sodium, even within ultra-processed categories. If industrial processing itself shows an independent effect, it strengthens the case for advising people to limit ultra-processed foods as a group, not just “clean them up” nutritionally.
For now, this trial is a critical step toward answering a question that has hovered over nutrition science for years: Can we make peace with some ultra-processed foods if we fix their nutrient deficiencies, or is the processing itself part of the problem?
Medical Disclaimer: This article is for educational purposes only and is not medical advice. Anyone with existing heart disease, high blood pressure, diabetes, or other medical conditions should consult a qualified healthcare professional before making major changes to their diet.
