Last week’s Stronger By Science podcast was apparently a “live event” on youtube. I missed the excitement, but now I’ve gotten a chance to listen the old-fashioned way, I wanted to be sure to update the conversation about the constrained energy expenditure model. If you’re new this topic, it began with the publication of Herman Pontzer’s book, Burn, which introduces the science behind the development of this model. Here is how I summarized constrained energy expenditure when I reviewed his book:
“To put it as simply as I can, he uses research, including extensive doubly-labeled water experiments, to conclude that human metabolism doesn’t simply use up more energy ad infinitum as we do more activity. Rather, the amount of energy we use in a day or week reaches a sort of equilibrium, and as we put more energy towards activities, we partition less energy towards other tasks within the body.“
This is not the first time the SBS gents have discussed constrained energy expenditure and the research Herman Pontzer has been a part of. In fact, this is the third episode in which it’s come up.. Since their initial conversation, there have been several studies that have gotten a lot of attention, and this latest study is described by Greg to have the following findings: there was a 72% average energy increase for people when they increase activity levels. In other words, for 100 calories of energy expenditure, 28 goes to compensation, 72 goes to activity. He also said that they witnessed more compensation for folks with larger BMIs (closer to 50%).
I am still waiting for a fuller conversation about this model from Eric and Greg, as I feel that they are oversimplifying the conclusions people are drawing from Burn and the research supporting it, basically saying the shorthand version is that exercise never increases how much energy we expend.
Greg responds to this oversimplification of Pontzer’s model by stating he finds it extremely surprising that there are folks who take Pontzer’s model to mean that we can compensate 100% for exercise and there is no increased energy expenditure. What I’m trying to figure out is if those of us who read Ponzter’s book and walked away with the conclusion that most of our energy expenditure can become compensated for are misunderstanding Pontzer’s conclusions, or if Greg is simply in disagreement with the findings as they’re presented in the book. I would feel better going back to an energy-modified-but-not-dramatically-constrained description of the findings if I can be shown that I misread Ponzer’s own conclusions as presented. For context, here’s another quote from my original post on this topic:
“Pontzer points out that this notion that energy expenditure is constrained leads to a natural conclusion, that habitual exercise and activity has very little impact on the number of calories we expend in a day. However, ‘exercise doesn’t change the number of calories you burn each day, but it does change how you spend them–and that makes all the difference.” (p237) It “has wide-ranging effects on how our metabolism is managed and where our calories are spent. . . ‘ (p 241) “
So, if I have concluded that Pontzer’s research says we do not expend dramatically more energy when we habitually have more movement in our lives, am I misunderstanding or is Greg in disagreement? I am open to evidence that I have missed an important concept in the book. I acknowledge, I’m not an expert in energy modeling. What doesn’t convince me are the anecdotes about folks expressing short bouts of increased energy expenditure followed by large amounts of eating without weight gain. My understanding of the model is that these brief moments of increased energy expenditure do indeed cost more energy. It’s due to chronic levels of increased activity that our bodies adapt and ultimately may not dramatically increase our energy expenditures. I will say Pontzer spends a whole chapter basically saying, well, if you’re not really gonna lose weight with exercise, here’s the other reasons you should do it anyway, which certainly contributed to my interpretation of his research.
I go back to my original desire for Greg and Eric to spend some time with this book and the larger body of the research in hopes of either having my misunderstandings cleared up or having their concerns addressed. I have a lot of respect for both of them and their abilities to consider a full body of research before drawing conclusions. Pontzer’s research and the data coming out of the doubly-labeled water database is some of the most interesting research happening right now. I look forward to learning more.
Update: Greg reached out to me and said he was responding to the oversimplification of the argument that he keeps encountering with people, folks concluding that exercise has no impact on energy expenditure. I find that a relief, as I also agree that is an oversimplification! I look forward to a more detailed conversation when they are able to make it happen.
Have something to say about the constrained energy expenditure model? I’d love to hear from you. You can leave a comment below, or join the conversation on Facebook–find and follow Progressive Strength!
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