Ultra-processed foods: what the Lancet series says

A three-paper Lancet series published from November 2025 argues that ultra-processed foods are displacing traditional diets worldwide and are linked to harm across nearly all organ systems. Its lead paper draws on more than 100 prospective studies, meta-analyses and randomised trials. The authors and their critics agree on one thing: most of that evidence is observational, so causation is still being argued.

What does the Lancet series claim about ultra-processed foods?

The lead paper, by Carlos Monteiro of the University of São Paulo and international colleagues, makes three core claims, according to its abstract:

1. Diets built on whole foods are being replaced by ultra-processed options around the world, a conclusion based on decades of national food surveys and recent global sales data.
2. The nutritional quality of diets is deteriorating through several mechanisms, including nutrient imbalances, overeating driven by high energy density, hyper-palatability and soft texture, and lower intake of beneficial plant compounds.
3. More than 100 prospective studies, meta-analyses and randomised trials link ultra-processed food consumption to adverse outcomes across nearly all organ systems.

According to FoodNavigator’s summary of the series, the associations were consistent, strong and grew with higher consumption for obesity, cardiovascular disease, type 2 diabetes, chronic kidney disease, Crohn’s disease and depression. Consumption also surged globally between 2007 and 2022. The other two papers in the series address policy and public health responses.

Where is the evidence weaker?

On cause and definition. FoodNavigator notes that many of the studies reviewed were observational, which shows correlation rather than causation. Some critics argue that poorer outcomes may stem from the nutrient content of these foods rather than the processing itself. The category itself is a broad grouping of very different products, which is one reason the debate over definitions continues.

Two readings can both hold at once. A large, consistent set of observational associations is worth taking seriously. And a diet pattern is a bundle of exposures, so untangling processing from nutrient content and from what people eat instead is hard. The US Dietary Guidelines for 2025 to 2030 named “highly processed foods” for the first time, so the topic is now in official guidance as well as in the research literature.

What population studies cannot show is how one person’s own markers, such as blood pressure, glucose and lipids, respond to changing what they eat. That is a measurement question, and the answer varies between people.

The bottom line

• The lead Lancet paper draws on more than 100 prospective studies, meta-analyses and randomised trials linking ultra-processed food to adverse outcomes across nearly all organ systems.
• Associations were described as consistent, strong and increasing with higher consumption, but most evidence is observational.
• Critics argue nutrient content, not processing, may explain part of the effect, and the definition of “ultra-processed” is contested.