What’s making us fat?

Simple: eating too much and exercising too little. Despite constant debate over which dietary villain to blame—fat, carbs, sodium, sugar—obesity is primarily a problem of calorie intake. The average adult is eating about 300 more calories per day than in the 1970s. In 2015, for the first time, Americans spent more money eating away from home than they did on groceries, and research indicates people eat 20 to 40 percent more calories at restaurants, where portion sizes have quadrupled since the 1950s, according to the Centers for Disease Control. American calories are also largely “empty” ones—highly processed foods such as chips, white bread, and sugary cereals account for almost 60 percent of U.S. calorie consumption. Those foods, plus artificial sweeteners, may disrupt nerve signals between the gut and the brain, causing us to keep eating long after we’ve had enough. As Yale University neuroscientist Dana Small explains, it’s as if “the brain doesn’t really know the food is even there.”