Dr. Levine is a Mayo Clinic endocrinologist and nutritionist who, like my favorite CDE, keeps on inspiring me. When I read his paean to physical inefficiency a year ago, I began to take pleasure in all the little nonexercise activity that makes up my daily life. I wrote about it here at "Inefficiency is NEAT" as well as an entire chapter of my new book.
I give Dr. Levine lots of the credit for starting me on the road from being a rather sedentary guy to a quite active one. No hypocrite himself, Dr. Levine mounted his computer over a treadmill so that he can walk slowly while he works.
His new study (with five co-authors) elegantly and precisely shows that the difference between being lean and obese is that lean people walk about two hours per day more. People who are obese simply make shorter walks, not fewer or slower walks.
This study, "The Role of Free-Living Daily Walking in Human Weight Gain and Obesity," appears in the March 2008 issue of Diabetes on pages 548-554. Only the abstract and a data appendix are online. But Dr. Levine was kind enough to send me a copy of the full-text of the article.
Dr. Levine and his colleagues started by studying how much their volunteers walked during the first 10 days of the study. Some of them were lean and some were obese, but on the average they took 47 short walks per day. While that may sound like a lot of walks, all of the volunteers wore sensors that could tell when their walk was for as little as a half second, although the doctors only counted walks of 2 seconds or more.
The walks typically were quite slow too. For 88 percent of the time they were about 2 miles per hour or less.
Then, the study moved to an overfeeding phase. For eight weeks all of the volunteers had to eat 1,000 calories more than they needed to maintain their weight. They ate everything at the Mayo Clinic General Research Center's metabolic kitchen. Otherwise, they kept on with their normal work, their hobbies, and their other activities.
As these volunteers put on weight, the distance that they walked decreased by 1 1/2 miles per day because they didn't walk as far. It didn't matter whether the volunteers were lean or obese at the start of the study.
I wonder if it is because it takes more energy to digest an extra 1,000 calories a day. This would take energy that the volunteers could otherwise use for walking. I think about this energy that we need for digestion or for exercise as a zero-sum game.
Those volunteers who were obese walked one-third as far as the lean ones. The difference was that their walks were one-third shorter.
I'm not a fast walker. But that doesn't seem to matter much. The lessons I learned from this study include that it's OK that I walk slowly as long as I devote an adequate amount of time to walking. I really see now how much sense that it makes to park at the far end of the parking lot, as people have been telling me to do for years, as well as to do a lot of other little, apparently inefficient things too.