Why have Americans become more obese?

I've been reading a lot about urban economics lately.  It's highly likely that this topic will come up at some point again in a future blog post, but suffice it to say that I recently enjoyed two great books by the Harvard economist Edward Glaeser, Triumph of the City: How Our Greatest Invention Makes Us Richer, Smarter, Greener, Healthier, and Happier and Survival of the City: The Future of Urban Life in an Age of Isolation.  Glaeser co-wrote the second book with another Harvard economist, David Cutler.  The second book referenced a study that Glaeser and Cutler published in 2003 in the Journal of Economic Perspectives, along with one of their graduate students, Jesse Shapiro, which was entitled "Why Have Americans Become More Obese?  The article is well worth a read, as it proposes one hypothesis for the obesity epidemic that I haven't heard in the past.  Cutler, Glaeser, and Shapiro argue that obesity is higher in America today because the economic cost (in terms of time) to prepare the food we eat has significantly decreased!

So, first let's look at how things have changed over time.  The average adult male weighed 168 pounds in the early 1960's.  Today, the average adult male weights 180 pounds.  Similarly, the weight of the average adult female increased from 143 pounds to 155 pounds during that same period of time.  Obesity is measured using the Body Mass Index, or BMI, which is calculated as the weight in kilograms divided by the height in meters squared.  Individuals with a BMI greater than 25 are classified as overweight, while individuals with a BMI greater than 30 are classified as obese.  Over the last four decades, the percentage of individuals who are considered either overweight or obese based on this measure has increased from 45 to 61 percent!

Even our impression of obesity has changed over time.  Just take a look at the following photograph which compares what childhood obesity looked like in the 1970's (at least according to the movies) versus today.  The photograph compares the "obese" character Augustus Gloop ("What do you get when you guzzle down sweets?  Eating as much as an elephant eats...") from the original Willie Wonka and the Chocolate Factory film from 1970 to the same character from the 2005 remake.

There have been a number of explanations suggested for the rising levels of obesity amongst Americans today.  For example, the American journalist Gary Taubes has suggested that our consumption of carbohydrates, particularly processed sugar and especially high-fructose corn syrup is to blame (read about his theory in Good Calories, Bad Calories, Why We Get Fat, and The Case Against Sugar).  I suspect this is partly the answer.  Cutler, Glaeser, and Shapiro point out that the 10 to 12 pound increase in median weight observed over the last few decades only takes a net caloric imbalance of about 100 to 150 calories per day.  That's like eating just three extra Oreo cookies or drinking one can of Regular Coca Cola a day!

They reviewed several different data sources and found that (1) consumption increased by about 268 calories per day for males and 143 calories per day for females and (2) most of this increase is from calories consumed during snacks.  In other words, we are eating about the same amount of calories during breakfast, lunch, and dinner, but it's the snacking that is responsible for our weight gain!  The average number of snacks per day increased by about 60 percent over the last few decades, and a major reason for this is the simple fact that food is more readily available than it was during the 1960's to 1970's.  Think about it.  We used to have to spend a lot of time (and energy) preparing our food.  Cutler, Glaeser, and Shapiro note that the time involved in preparing the food that we eat has fallen by half in the past 30 years.  

Today, just about everything we would want to eat is readily available for purchase in a "ready to eat" form at our local supermarket.  Microwaves have made cooking our food a lot easier.  The vast majority of households in the U.S. now own microwave ovens, which significantly cuts down the time required to prepare food and/or reheat leftovers.  

I know that I have to pay close personal attention to avoid snacking too much between meals.  Whenever I've lost weight in the past, it's not because I've cut down the number of calories during breakfast, lunch, or dinner.  It's because I've cut down (or even eliminated) the calories that I've consumed between meals.  Based on my own experience then, the study by Cutler, Glaeser, and Shapiro is very compelling.  

Take a look at the study and let me know what you think!