Tuesday, May 27, 2008

Exercise Didn't Keep Us From Getting Fat

One of the surprising things I noticed when I was poring over data from the NHANES survey (US CDC National Health and Nutrition Examination Survey) from 1975 to 2006 is that the number of inactive people has diminished in that same time period from 50% to 24%. This is shocking to most people. We have this romanticized idea that in the 1970s people were more active, as if everyone chopped wood and walked 15 miles to work in the morning. The reality is, there were office jobs, housewives and cars without the large numbers of runners and gym-goers we have today.

Granted, NHANES data are self-reported and should be taken with a grain of salt. However, Chris at Conditioning Research pointed me to a study looking at changes in energy expenditure from the 1980s to the present in North America and Europe. It doesn't suffer from the same biases because it's based on direct measurement rather than self-reporting. Here's the executive summary: we're expending slightly more energy than we used to, partly because we exercise more and partly because it takes more energy to move our heavier bodies around.

I'm certainly not blaming the obesity problem on an increase in physical activity, but I do think we can safely rule out inactivity as the reason we've gotten fatter. In my mind, this only leaves one major possible cause for the obesity epidemic: changes in diet. Don't get me wrong, I think exercise is good. It has numerous positive effects on physical and mental health. But it's not as powerful of a tool for fat loss and general health as diet.

Anecdotally, I do know several people who lose fat when they exercise regularly. I also know some who don't lose fat when they exercise. Exercise and a healthy diet converge on some of the same metabolic pathways, such as sensitivity to insulin. But diet changes are far more effective than exercise at correcting metabolic problems. The reason is simple: the problems a person corrects with a good diet are caused by a poor diet to begin with.


4 comments:

reid said...

I guess the next logical step would be to look at how diet has changed from the 1970s to today. My guess would be that we consume much more carbs and processed foods today. It's unfortunate that despite advances in science and technology we as a nation haven't improved our understanding of what truly constitutes a healthy diet.

Stephan said...

Reid,

I have some information on diet changes in that time period in my fructose post. It's hard to know how accurate that information is though. It's from USDA estimates, which is probably more accurate than self-reporting but not perfect. We're eating more sugar, more carbohydrate in general, more processed wheat/corn/soy products, more skim milk, less whole milk, more vegetable oil but the same amount of total fat.

Nick said...

In general, I think there a lot of frustrated health-conscious in this country, particularly women. And it must be incredibly frustrating to follow the FDA health recommendation "pyramid" to a tee--in an effort to remove any and all dietary fat and replace it with complex carbohydrates--yet not achieve long-term weight loss or cardiovascular health. Manufacturers proudly display captions on the front of their products that say things like:
"95% fat free"
"Fat free"
"Low cholesterol"
"Whole wheat"
"100% bran"
"High fiber"
And people go crazy for these catchwords and gobble up tons of energy bars, granola and "Special K" cereals, yogurt, skim milk, breads and pastas, sugary fruits, and other carbohydrate-loaded snacks. They strive to remove eliminate all fats and meats from their diets, only to replace them with carbohydrates, which is actually the biggest contributor to obesity due to insulin production. Next time you see the "Slim Fast" drink in the store, notice how many grams of carbohydrates it contains. And people wonder why their diets fail. Very frustrating indeed.

Stephan said...

Nick,

Good point, crap food definitely masquerades as health food all too often. You can't make piles of money off the health conscious demographic by selling them carrots.