Ultra-processed foods have become a hot topic in nutrition debates. As usual, riddled with hyperbole. But what does the science actually say about ultra-processed foods and weight gain?

What Are Ultra-Processed Foods?

Defining ultra-processed foods is more challenging than you might think. We do not have a universally accepted, objective method to classify foods along the processing spectrum. The most widely used framework is the NOVA classification system, which categorizes foods into four groups based on the extent and purpose of industrial processing (Monteiro et al., 2019).

According to NOVA, ultra-processed foods (Group 4) are industrial formulations typically containing five or more ingredients, including substances not commonly used in home cooking—such as hydrolyzed proteins, modified starches, hydrogenated oils, and various additives like emulsifiers, colorants, and flavor enhancers. Examples include soft drinks, packaged snacks, reconstituted meat products, and many ready-to-eat meals.

Here is the critical point: NOVA classification tells us about the degree of processing, not necessarily about nutritional quality or healthfulness. The system is descriptive, not prescriptive. It doesn’t account for nutrient density, portion sizes, or how foods fit into an overall dietary pattern.

This creates some puzzling categorizations. A protein bar fortified with vitamins and minerals might be classified as ultra-processed, while sugar or butter—which undergo minimal processing—would not be. Whole grain bread from a bakery might be minimally processed, but the same bread from a factory could be ultra-processed based solely on production scale and ingredient list length.

The NOVA system was not designed to be a direct measure of health outcomes, yet it is often interpreted that way in popular discourse (Gibney, 2018).

A Landmark Study

To understand whether ultra-processed foods directly cause weight gain, we need to look at controlled research. The study by Hall et al. (2019) provides crucial insights.

In this randomized controlled crossover trial conducted in a metabolic ward, 20 adults were provided either an ultra-processed diet or an unprocessed diet for two weeks, then switched to the opposite diet for another two weeks. The diets were carefully matched for calories, sugar, fat, fiber, and macronutrients—they were nutritionally equivalent on paper.

The results were striking: participants consumed approximately 500 more calories per day on the ultra-processed diet and gained about 0.9 kg (2 lbs), while they lost a similar amount on the unprocessed diet. Participants ate faster on the ultra-processed diet and consumed more calories before reporting feeling full.

This suggests that ultra-processed foods may promote overconsumption even when their nutrient composition matches whole food alternatives. Potential mechanisms include differences in eating rate, energy density, palatability, and satiety signaling.

The UPDATE Trial

Further investigations into UPFs have been made - the recently published UPDATE trial (Dicken et al., 2025) investigated whether ultra-processed foods affect weight and health outcomes when both diets follow national dietary guidelines. In this 8-week crossover trial, 55 adults with overweight or obesity in the UK were provided with either a minimally processed food (MPF) diet or an ultra-processed food (UPF) diet—both designed to follow the UK Eatwell Guide recommendations.

The results showed that both diets led to weight loss: participants lost 2.06% of their body weight on the MPF diet and 1.05% on the UPF diet. While the MPF diet resulted in significantly greater weight loss and fat mass reduction, the critical finding is that the UPF diet—when aligned with healthy eating guidelines—still produced weight loss and improvements in several cardiometabolic markers.

This real-world study demonstrates that when ultra-processed foods are selected to meet nutritional recommendations (lower in saturated fat, sugar, and salt; adequate fiber and vegetables), they can be part of a weight loss strategy. However, minimally processed foods appear to offer additional benefits for body composition and appetite control.

The Benefits of Ultra-Processed Foods

So rather than dismissing ultra-processed foods entirely, we should acknowledge their legitimate benefits:

Convenience: Time-pressed individuals and families often rely on convenient options to maintain consistent eating patterns rather than skipping meals entirely, or eating at restaurants/fast-food – which can pose a separate set of challenges.

Cost: Many ultra-processed foods are shelf-stable and economical, making adequate nutrition more accessible for budget-conscious consumers.  

Nutrient Fortification: Many ultra-processed foods are fortified with essential vitamins and minerals (iron, folate, vitamin D, calcium), which can help address nutrient gaps, especially in at-risk populations.

Taste and Palatability: These foods are engineered to taste good, which can support dietary adherence for some individuals, and provide greater fulfillment from meals.

The Food Matrix Matters

That said, there is growing evidence that foods are more than the sum of their parts. The concept of the “food matrix” recognizes that the physical structure and chemical interactions within whole foods affect how nutrients are absorbed and utilized by the body (Fardet, 2015).

For example, the fiber, phytochemicals, and physical structure of an apple work synergistically in ways that apple juice—even if fortified—cannot replicate. The protein in a piece of chicken breast exists within a complex matrix of connective tissue, fat, and micronutrients that may be altered through extensive processing.

Reducing foods to purely their nutrient composition might not convey the same metabolic, satiety, or health benefits as consuming the whole food version. This is why whole foods should form the foundation of a healthy diet.

The Bottom Line

So, do ultra-processed foods cause weight gain? The answer is: it depends.

Ultra-processed foods may promote overconsumption due to their palatability, energy density, and effects on eating rate and satiety. However, they are not inherently fattening, and they can be included in a dietary pattern that supports weight loss and health improvements.

It is generally advisable to have most of your diet come from whole, minimally processed foods. These foods provide superior satiety, nutrient density, and the benefits of an intact food matrix. But ultra-processed foods can play a role in a healthy dietary pattern—and in some cases, they can help facilitate weight loss and better health outcomes by improving adherence, convenience, and accessibility.

The most important principle is this: an individual’s diet should be individualized. There is no one-size-fits-all approach. Your optimal dietary pattern depends on your health goals, lifestyle, preferences, budget, cooking skills, and cultural background.

At Redesign Nutrition, we specialize in creating personalized nutrition plans that work for your life—not someone else’s ideal. We help you navigate the complex food environment, make informed choices, and build sustainable habits that support your health and weight goals.

Sincerely,

Kevin Rogers, RDN, LD

Founder | Redesign Nutrition

References

Dicken, S., Makaronidis, J., van Tulleken, C., Jassil, F. C., Hall, K., Brown, A. C., Gandini Wheeler-Kingshott, C. A. M., Fisher, A., & Batterham, R. (2024). UPDATE trial: investigating the effects of ultra-processed versus minimally processed diets following UK dietary guidance on health outcomes: a protocol for an 8-week community-based cross-over randomised controlled trial in people with overweight or obesity, followed by a 6-month behavioural intervention. BMJ open, 14(3), e079027. https://doi.org/10.1136/bmjopen-2023-079027

Fardet, A. (2015). A shift toward a new holistic paradigm will help to preserve and better process grain product food structure for improving their health effects. Food & Function, 6(2), 363-382. https://doi.org/10.1039/c4fo00477a

Gibney, M. J. (2018). Ultra-processed foods: Definitions and policy issues. Current Developments in Nutrition, 3(2), nzy077. https://doi.org/10.1093/cdn/nzy077

Hall, K. D., Ayuketah, A., Brychta, R., Cai, H., Cassimatis, T., Chen, K. Y., … & Zhou, M. (2019). Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of ad libitum food intake. Cell Metabolism, 30(1), 67-77. https://doi.org/10.1016/j.cmet.2019.05.008

Monteiro, C. A., Cannon, G., Levy, R. B., Moubarac, J. C., Louzada, M. L., Rauber, F., … & Jaime, P. C. (2019). Ultra-processed foods: What they are and how to identify them. Public Health Nutrition, 22(5), 936-941. https://doi.org/10.1017/S1368980018003762