I’ve been amazed at how restaurant portion sizes have grown over the years and based on this Bloomberg story by Cass R. Sunstein, I’m not the only one.

According to the Centers for Disease Control and Prevention, the average U.S. restaurant meal is more than four times larger than it was in the 1950s. The average hamburger, once less than 4 ounces, is now more than 12 ounces. The average order of French fries, once less than 3 ounces, is now more than 6 ounces. There is a clear correlation between increases in portion sizes and increases in obesity.

That correlation helps explain why obesity has been more prevalent in the U.S. than in France. The French eat high- calorie food, but their portion sizes are smaller. In supermarkets and restaurants, and in portion sizes recommended in cookbooks, Americans are given significantly bigger servings. Even at McDonald’s, where we might expect identical sizes, servings of soda and French fries have been found to be larger in Philadelphia than in Paris.

Brian Wansink, a Cornell University professor of consumer behavior, helps to explain why portion sizes have such a large effect. He finds that much of our eating is mindless or automatic in that we tend to eat whatever is in front of us. If you are given a half-pound bag of M&M’s, chances are that you will eat about half as much as you will if you are given a one- pound bag. People who receive large bowls of ice cream eat a lot more than those who get small bowls.

In one of Wansink’s fiendish experiments, people were provided with a large bowl of Campbell’s tomato soup and told to eat as much as they liked. Unbeknownst to them, the soup bowls were engineered to refill themselves (with empty bottoms connected to machinery beneath the table). No matter how much soup the subjects ate, the bowl never emptied. The result? Soup consumption skyrocketed. Many people just kept eating until the experiment was ended.

Some this behavior is probably learned. From a very young age, children are taught to “clean your plate” (sometimes backed up by “there are starving people in China”). Nonetheless, carrying this practice over into adulthood can be a real problem for people who eat out a lot.

We don’t eat out much except when we travel (and that presents a few challenges), but I was simply amazed when they started putting nutritional information on menus – I couldn’t believe how many calories, carbs, salt, etc. restaurants are piling into their entrees.