FOOD shopping has become a dangerous pursuit. Nutritional horrors lurk on every shelf. Ready-meals are packed with salt and preservatives, breakfast cereals are sweeter than chocolate bars, and processed meats are packed with nitrite-preservatives, which can form harmful compounds when cooked. A new term is catching on to describe these nutritional bad guys: ultra-processed foods (UPFs). In his new book, Ultra-Processed People, Chris van Tulleken, a doctor and television presenter, argues that UPFs dominate the food supply in rich countries, and are also creeping into diets in low- and middle-income countries. As they proliferate, so do concerns about their effects on human health. Just how bad are UPFs, and what do they do to us?

The concept of UPFs was devised by Carlos Monteiro, a Brazilian scientist, in 2009. His team of nutritionists observed that although people in Brazil were buying less sugar and oil, rates of obesity and type-2 diabetes were rising. That was because they were instead eating more sugar, fats and additives in packaged snacks and pre-made meals. In response, Monteiro proposed a food classification system to take into account the degree of processing involved in the food supply.

Processing can make healthy foods unhealthy: fruit, for instance, goes from healthy to unhealthy as it is desiccated, squeezed or sweetened. Monteiro’s system, called Nova, puts foods into four “buckets”: unprocessed and minimally processed foods; processed culinary ingredients; processed foods; and ultra-processed foods. This allows more fine-grained distinction between different degrees of processing. Thus staples such as rice, oil or flour, which all require minimal processing for consumption, do not belong in the same category as a Twinkie.