In the Trump administration’s quest to “Make America Healthy Again,” there may be no bigger target than ultraprocessed foods. Robert F. Kennedy Jr., the nation’s new health secretary, has cited “highly chemically processed foods” as a chief culprit behind an epidemic of chronic disease in the U.S., including ailments such as obesity, diabetes and autoimmune disorders. Such foods are “poisoning” people, particularly children, Kennedy said during Senate confirmation hearings. He has vowed to work to remove such foods from federal programs such as the Supplemental Nutrition Assistance Program, or SNAP. “I will do everything in my power to put the health of Americans back on track,” he told lawmakers. Key to that goal, however, could be making sure that consumers understand basic facts about ultraprocessed foods and the role they play in daily meals. From sugary cereals at breakfast to frozen pizzas at dinner, plus in-between snacks of potato chips, sodas and ice cream, ultraprocessed foods make up about 60% of the U.S. diet. For kids and teens, it’s even higher — about two-thirds of what they eat. That’s concerning because ultraprocessed foods have been linked to a host of negative health effects, from obesity and diabetes to heart disease, depression, dementia and more. One recent study suggested that eating these foods may raise the risk of early death. Nutrition science is tricky, though, and most research so far has found connections, not proof, regarding the health consequences of these foods. Food manufacturers argue that processing boosts food safety and supplies and offers a cheap, convenient way to provide a diverse and nutritious diet. Even if the science were clear, it’s hard to know what practical advice to give when ultraprocessed foods account for what one study estimates is 73% of the U.S. food supply. Most foods are processed, whether it’s by freezing, grinding, fermentation, pasteurization or other means. In 2009, Brazilian epidemiologist Carlos Monteiro and colleagues first proposed a system that classifies foods according to the amount of processing they undergo, not by nutrient content. At the top of the four-tier scale are foods created through industrial processes and with ingredients such as additives, colors and preservatives that you couldn’t duplicate in a home kitchen. “The more ultraprocessed the food is, the more it's likely to encourage you to eat more than you realize or want to eat,” said Marion Nestle, a nutritionist and food policy expert. However, the level of processing alone doesn’t determine whether a food is unhealthy or not. Whole-grain bread, yogurt, tofu and infant formula are all highly processed, for instance, but they’re also nutritious. Many studies suggest that diets high in such foods are linked to negative health outcomes. But these kinds of studies can’t say whether the foods are the cause of the negative effects — or whether there’s something else about the people who eat these foods that might be responsible. Ultraprocessed foods, as a group, tend to have higher amounts of sodium, saturated fat and sugar, and tend to be lower in fiber and protein. It’s not clear whether it’s just these nutrients that are driving the effects.