Ultra-Processed Foods and Human Health

Leon Wirz
Dec 29, 2025
4 min read

The Lancet (December 2025) | University of São Paulo, Harvard T.H. Chan School of Public Health, University of Sydney & international collaborators

Introduction

For decades, nutrition science focused mainly on nutrients: calories, sugar, fat, and vitamins. More recently, a different question has gained importance: how food is processed before it reaches our plate.

A comprehensive scientific review published in The Lancet in December 2025 examines the health effects of ultra-processed foods. Led by researchers from the University of São Paulo, with contributions from institutions including Harvard T.H. Chan School of Public Health, the University of Sydney, and several European research centres, the paper brings together decades of evidence from population studies, experiments, and mechanistic research.

The conclusion is clear: diets dominated by ultra-processed foods are increasingly replacing traditional diets and are strongly associated with a wide range of chronic diseases.

The Core Discovery

The authors test three closely connected hypotheses.

First, ultra-processed foods are steadily displacing long-established dietary patterns based on whole and minimally processed foods. This trend is observed across most regions of the world.

Second, this shift leads to a broad deterioration in diet quality. Ultra-processed diets are typically higher in free sugars, unhealthy fats, and energy density, while being lower in fibre, micronutrients, and health-protective plant compounds.

Third, high exposure to ultra-processed diets increases the risk of multiple chronic diseases. Across more than 100 long-term studies, higher intake is consistently associated with obesity, type 2 diabetes, cardiovascular disease, chronic kidney disease, depression, and increased all-cause mortality.

Taken together, the evidence supports the conclusion that ultra-processed foods are not just “unhealthy choices,” but part of a dietary pattern that systematically increases disease risk.

How the Study Was Conducted

This paper combines multiple lines of evidence.

The authors analysed national food intake and purchase surveys spanning several decades, global food sales data from 93 countries, and conducted a systematic review and meta-analysis of 104 prospective cohort studies. Participants in these cohorts were followed for up to 46 years.

In addition, evidence from short-term randomised controlled feeding trials and mechanistic studies was included to assess biological plausibility.

Foods were classified using the NOVA classification system, which groups foods according to the extent and purpose of industrial processing rather than nutrient content alone. Exposure was measured as the proportion of total dietary intake coming from ultra-processed foods.

Key Findings

Several findings stand out for their consistency.

Diets high in ultra-processed foods are associated with poorer nutrient profiles and reduced intake of fruits, vegetables, and legumes. They are also linked to higher total energy intake.

Randomised feeding trials show that people consume significantly more calories when eating ultra-processed diets, even when meals are matched for sugar, fat, salt, and fibre. This leads to rapid weight and fat mass gain.

Long-term observational studies link high ultra-processed food intake to increased risk of cardiometabolic diseases, gastrointestinal and kidney disease, mental health disorders, and premature death. These associations remain even after adjusting for traditional measures of diet quality.

Limitations of the Study

As with most large-scale nutrition research, important limitations need to be considered.

Much of the evidence linking ultra-processed foods to chronic disease is observational. This means that absolute causality cannot be proven in the same way as in long-term randomised trials. People who consume more ultra-processed foods may also differ in other ways, such as physical activity, socioeconomic status, or overall lifestyle, which can never be fully accounted for statistically.

There are also challenges related to food classification. The NOVA system relies on ingredient lists and descriptions of food processing, which can be imperfect when dietary surveys lack detail. Some foods sit close to category boundaries, and misclassification is possible, particularly for mixed or reformulated products.

However, these limitations are partly addressed by the breadth and consistency of the evidence. Associations are observed across countries, age groups, and study designs, and they persist even after adjustment for key nutrients and overall diet quality. Importantly, controlled feeding trials show that ultra-processed diets lead to higher calorie intake and weight gain even when nutrient profiles are matched, supporting biological plausibility.

Finally, large, long-term randomised trials of whole dietary patterns are rarely feasible for ethical, financial, and practical reasons. In this context, public health decisions often rely on converging evidence from multiple sources rather than a single definitive experiment.

Relevance for Switzerland

Switzerland performs well on many health indicators, but the trends described in this study are clearly relevant.

Ultra-processed foods already make up a meaningful share of the Swiss diet, especially among younger adults and working households. This shift is driven less by lack of knowledge and more by time pressure, convenience, and modern work patterns.

From a health-system perspective, this matters because Switzerland’s healthcare costs are largely driven by chronic diseases such as diabetes, cardiovascular disease, kidney disease, and depression. The Lancet evidence shows that ultra-processed dietary patterns increase risk across exactly these conditions.

Even small increases in long-term disease risk can translate into substantial costs in a high-cost system like Switzerland’s. Because diet-related risks accumulate slowly, the consequences often appear years after exposure, when prevention is already difficult.

Potential Impacts of a Successful Dietary Shift

Reducing reliance on ultra-processed foods could lower the incidence of chronic disease over time, slow growth in healthcare expenditures, and improve quality of life in older age.

For insurers and public health systems, even modest improvements in population-level diet quality could have meaningful long-term benefits.

Risks

A key risk is delay. Waiting for perfect mechanistic certainty may allow preventable disease burdens to grow.

There is also a risk of oversimplification. Ultra-processed foods vary widely, and not all traditional foods are healthy. Policies and recommendations must therefore be proportionate and evidence-based.

Overall Assessment

This Lancet paper represents one of the most comprehensive evaluations of ultra-processed foods to date. Its conclusions are supported by multiple, independent lines of evidence.

The findings suggest that ultra-processed foods should be understood not just as nutritionally inferior products, but as a central driver of modern chronic disease patterns.

What Comes Next

Further research will refine mechanisms and identify particularly harmful product categories. However, the authors argue that existing evidence is already strong enough to justify action.

For countries like Switzerland, the challenge is no longer whether ultra-processed foods matter, but how to address their impact early, before long-term health and cost consequences become entrenched.

Reference

Ultra-processed foods and human health: the main thesis and the evidence Link

Monteiro, Carlos A et al.

The Lancet, Volume 406, Issue 10520, 2667 - 2684