Tuesday, May 27, 2008

Obesity research 1

There were a couple of interesting studies this month in the International Journal of Obesity:

Physical activity energy expenditure has not declined since the 1980s and matches energy expenditures of wild mammals - so the fatties can't blame it all on their "sedentary lifestyle". If you want to lose fat, you are going to have to get serious with your diet - what you eat and how much of it you scoff. It reminds me a little of Taubes piece here, and Matt's comments : Food versus Exercise

Objective: Obesity results from protracted energy imbalance. Whether this comprises excessive energy intake, lowered physical activity or both, remains disputed.
Design: Physical activity energy expenditure, evaluated in three different ways from daily energy expenditure (DEE) measured using doubly labelled water, was examined for trends over time. Data included subjects in Europe (Maastricht, the Netherlands) and North America extending back to the 1980s. These data were compared with measures from the third world, and measures made on wild terrestrial mammals.
Results: Physical activity expenditure in Europe (residual of the regression of DEE on basal energy expenditure (BEE)) has slightly but significantly increased since the 1980s. There was no trend over time in physical activity level (PAL=DEE/BEE), or in the residual variance in DEE once mass, sex and age were accounted for. This latter index of physical activity expenditure also significantly increased over time in North America. DEE of individuals in Europe and North America was not significantly different from individuals measured in the third world. In wild terrestrial mammals, DEE mostly depended on body mass and ambient temperature. Predicted DEE for a 78 kg mammal living at 20 °C was 9.2 MJ per day (95% CI: 7.9–12.9 MJ per day), not significantly different from the measured DEE of modern humans (around 10.2–12.6 MJ per day).
Conclusion: As physical activity expenditure has not declined over the same period that obesity rates have increased dramatically, and daily energy expenditure of modern man is in line with energy expenditure in wild mammals, it is unlikely that decreased expenditure has fuelled the obesity epidemic.

UPDATE - Stephan has some helpful comments on this study: Exercise Didn't Keep Us From Getting Fat

6 comments:

Stephan said...

This is awesome, I came to the same conclusion when I was poring through US Centers for Disease Control NHANES data a few weeks ago. It blows away the idea that we're fat because we don't exercise, and leaves diet as the main culprit in my opinion. I'm going to do a post on this immediately because I think it's incredibly important. Thanks for the tip.

Chris said...

I will look forward to your post Stephan. I've just been away walking in the mountains for a week, not blogging this stuff and I must admit coming back that I wondered if I had the enthusiasm to keep doing this.

I find the research interesting, but I am no expert - my degrees are in Economic & Philosophy with a masters in management. I've been training with weights etc since 1983 when I was 15, but I am no scientist and rely on ones like you, Peter (Hyperlipid) and my girlfriend who is a research immunologist to keep me on the right lines.

I think I need to rethink this blog a bit. It is really just a place for me to record interesting things I find....

Stephan said...

Well if it helps at all, I get a lot out of your blog. I think there are more people that read it than the comments reflect. I wouldn't go out of my way to filter through all the latest conditioning research on PubMed, so having it summarized on your blog is very helpful.

Oh, and by the way I also just got back from a backpacking trip down in Oregon. We got stopped in our tracks by deep snow but it was still a great trip!

Chris said...

Thanks

Dr. B G said...

I've enjoyed your pieces as well :) Please don't give it up... or your interests! HeartCipher.com lead me over here so I must thank him profusely.

Have you or your girlfriend/immunologist ever considered thoughts on Lp(a) and its role in atherogenic damage in heart disease (and strokes)? I have a lot of questions... (and no bloggers to bug who are immunologists!!) *hint hint* just brilliant biochemists! (like Hyperlipid/Peter! *heh*)

Lp(a) is a fascinating enigma -- part cholesterol, part immune factor. Abundantly deadly for many people -- 25% of Americans -- maybe +50% of people in the Track Your Plaque program -- including several bloggers.

I'm gonna post soon about it -- but also like you -- i'm not a scientist and my immunology sucks.

What I don't get is -- Lp(a) certainly plays a vital role in quickly killing cancer or foreign bugs, but when it auto-attacks it becomes a slight problem.

How can acute phase reactions be controlled to control Lp(a)'s damaging effects? Or is it just a simple matter of stress/diet/body composition manipulations??

THANKS!
-G

Matt Metzgar said...

Chris,

This is such an interesting study. I'm going to have to take a deeper look at it. On the surface, I find it hard to believe energy expenditure hasn't dropped, but I could be wrong!