USDA reports: "Between 1977-78 and 2005-08, U.S. consumption of food prepared away from home increased from 18 to 32 percent of total calories. Meals and snacks based on food prepared away from home contained more calories per eating occasion than those based on at-home food. Away-from-home food was also higher in nutrients that Americans overconsume (such as fat and saturated fat) and lower in nutrients that Americans underconsume (calcium, fiber, and iron)." They cite a December 2012 report, "Nutritional Quality of Food Prepared at Home and Away From Home, 1977-2008," by Biing-Hwan Lin and Joanne Guthrie. That study finds: "In the past three decades, FAH [food at home] has changed more in response to dietary guidance, becoming significantly lower in fat content and richer in calcium, whereas FAFH [food away from home] did not."
Sure, it's possible to overeat dramatically at home, too. Sometimes people do sit down in front of the television with a family-sized bag of chips or a quart of ice cream. But most people wouldn't grill a burger or deep-fry chicken for lunch, not to mention the ubiquitous (and irresistable) french fries and a sugared soda. Most people don't go to a restaurant and buy an apple and a bowl of lentil soup, either. The causes of obesity are many and mixed, but it seems plausible that paying others to tempt us with food, rather than spending time ourselves to make food, is part of the pattern.