Dietary patterns high in ultra-processed foods (UPFs) have been associated with poor diet quality and health outcomes, and are displacing healthier dietary patterns-meals and dishes prepared with fresh and minimally processed foods-in most parts of the world. In the second paper of this Series, we propose a set of government policies aimed at halting and reversing the rise of UPFs worldwide. To date, policies have mainly focused on reducing consumption of foods high in added fats, sugar, and sodium, many of which are UPFs. However, we propose that these efforts be strengthened and expanded to address a broader set of food system drivers influencing the production, marketing, and consumption of UPFs. This Series paper addresses four food policy domains that correspond to the key dimensions of food system drivers of UPF production, marketing, and consumption: UPF products, UPF food environments, UPF manufacturers, fast-food corporations, and supermarket corporations retailers, and food supply chains. For each domain, we explore policy options and focus on large-scale food system measures that target areas in greatest need of change, and their potential impacts. We also examine policies to protect, incentivise, and support dietary patterns based on fresh and minimally processed foods, particularly for lower income households. Which policy actions governments decide to prioritise will depend on each country's level of UPF consumption, along with many other issues unique to each country. We emphasise the importance of advancing this agenda in all countries, irrespective of their development status, to promote healthier diets among populations.

This first paper in a three-part Lancet Series combines narrative and systematic reviews with original analyses and meta-analyses to assess three hypotheses concerning a dietary pattern based on ultra-processed foods. The first hypothesis-that this pattern is globally displacing long-established diets centred on whole foods and their culinary preparation as dishes and meals-is supported by decades of national food intake and purchase surveys, and recent global sales data. The second-that this pattern results in deterioration of diet quality, especially in relation to chronic disease prevention-is confirmed by national food intake surveys, large cohorts, and interventional studies showing gross nutrient imbalances; overeating driven by high energy density, hyper-palatability, soft texture, and disrupted food matrices; reduced intake of health-protective phytochemicals; and increased intake of toxic compounds, endocrine disruptors, and potentially harmful classes and mixtures of food additives. The third and final hypothesis-that this pattern increases the risk of multiple diet-related chronic diseases through various mechanisms-is substantiated by more than 100 prospective studies, meta-analyses, randomised controlled trials, and mechanistic studies, covering adverse outcomes across nearly all organ systems. The totality of the evidence supports the thesis that displacement of long-established dietary patterns by ultra-processed foods is a key driver of the escalating global burden of multiple diet-related chronic diseases. Two companion papers in this Series specify policy actions and wider public health strategies to promote, protect, and support diets based on fresh and minimally processed foods and prevent their displacement by ultra-processed foods.