Timothy Taylor finds a USDA report, which says that
Between 1977-78 and 2005-08, U.S. consumption of food prepared away from home increased from 18 to 32 percent of total calories.
Since 1970, the proportion of food spending that is spent on eating out has increased from about 25 percent to about 43 percent.
Taylor and the USDA focus on the consequences for obesity. I would add that this trend will increase measured GDP. When you spend time preparing a meal at home, it does not count as GDP. When you eat out, the time spent preparing the meal does count as GDP.
I believe that this represents a legitimate increase in GDP. My comparative advantage is not in food preparation. The same is true for most people. Spending less time in the kitchen represents economic progress.
Although I eat out much less than most people, I rarely spend more than 20 minutes preparing a meal. That means that I eat a lot of prepared foods. I do think that most meals that you eat at home have a higher ratio of nutrients to calories than most meals that you eat outside the home. Perhaps that will change at some point.