When it comes to losing weight or maintaining a healthy diet, many of us have chosen to go either low-calorie or low-fat. But recent research has started to upend nutrition science, reframing our notions of “healthy” eating, according to Dariush Mozaffarian, a cardiologist and Dean of the Friedman School of Nutrition Science and Policy at Tufts University.

Mozaffarian explains why the science is changing, when a calorie isn’t just a calorie, how fat could be a lot better than we think, and why he believes that government should play a much bigger role in influencing our food choices.