Interesting. Do you know the approximate percentage your body slows down its metabolism by?
I still see a benefit to exercise, especially cardio, when it comes to weight loss. I figure i burn 1500 passive calories a day by doing nothing. Most of my mountain bike rides burn 1500-2000 calories. Even if my resting metabolism slowed by 50% I’m way ahead of where I would otherwise be. At the very least it gives wiggle room for dietary lapses in judgement.
Does it talk about whether that applies to any exercise? Meaning moderate to high intensity vs. low intensity or is it any exercise? My totally anecdotal evidence is I’ve always had better success with low intensity/impact exercise. Walking, cleaning the house.
I finished the book a while ago and have been meaning to come back and comment further.
I will reaffirm that
the book is well written and interesting throughout. I highly recommend it. It's written by a true expert in his field -- a front-line researcher, not a journalist -- but the writing would be stellar even for someone who writes for a living.
There is no simple formula, like if you do X calories of work, your totally daily expenditure will increase by 0.35 * X (i.e., 35% of what you'd expect if your body were a simple machine).
Here's my basic summary of the book.
1. Exercise is really good for you -- just not really for reasons involving weight control.
Some of the reasons exercise is good for you are specifically related to the reasons it doesn't necessarily help with weight control. For example, chronic inflammation costs energy. You can't make your whole body all inflamed for free -- it takes calories to sustain the inflammation. It also takes calories to be really stressed out all the time. Regular exercise is very effective at reducing chronic inflammation and chronic stress -- which is great because those things are unhealthy. But one of the results is that regular exercise reduces your caloric expenditure on inflammation and stress, which somewhat offsets your increased caloric expenditure on exercise.
2. Long-term, our metabolisms adapt quite remarkably to our normal activity levels.
If you're trying to predict someone's daily energy expenditure (on a routine, unexceptional day), the main thing you'll want to know is their lean mass. There is variation among individuals, but lean mass is by far the most reliable indicator. After that, exposure to parasites might be the next largest factor (since immune response costs energy). Activity level, on the other hand, doesn't really tell you much. If you take two identical twins who are similar in most respects, but one walks 2 miles a day while the other walks 8 miles a day ... you can expect their daily energy expenditure to be pretty much identical. The guy who walks farther will spend more energy on walking, but less energy on inflammation, stress, etc. Your average Hadza hunter-gatherer walks about eight miles a day and does other physical activity as well, but burns the same number of calories each day as a size-matched modern American. This is an extremely surprising result, but it is robust -- tested in various ways, and not limited to just humans. It seems to be true for all mammals. Let one hamster run on a wheel for an hour a day and another for three hours a day, and after they are adapted to those activity levels, their daily energy expenditure will be similar (controlling for their size).
3. Adaptation takes a while.
The result I just mentioned occurs only after the animals are fully adapted to their activity levels. If I normally walk two miles a day, but today I walk eight miles, my energy expenditure today will be higher than normal by the amount it takes to walk the extra six miles. If I keep walking eight miles a day, my daily energy expenditure will slowly come back down to my former level (when I was walking just two miles a day), but it could take years for that to happen. In the short term, more activity means greater energy expenditure. In the long term, our bodies adapt to our normal activity levels and expend the energy predicted based on lean body mass. (There are some levels of activity that we can't adapt to. If you compete in the Tour de France every day, in the short term you will burn more energy than you can possibly consume. In the long term, you will die.)
4. Actually, exercise can help with weight control.
The point in #1 above has an asterisk. Metabolism is complicated. It's regulated largely by the hypothalamus. Our hypothalamus tries to match our calories in with our calories out in part by increasing or decreasing our appetite. If you exercise more than normal today, you'll work up an appetite and probably eat more than normal. (This is another reason why it's hard to use exercise to lose weight.) But that normal process can sometimes go haywire for reasons we don't totally understand, but it might have something to do with chronic inflammation, and in any case it's linked to sedentariness. If you just sit around on the couch all day, your hypothalamus will be confused and may tell you to eat more than you should. Your appetite may not be matched to your energy expenditure. For reasons we don't totally understand, exercise seems to help avoid that trap. Habitual exercise can rein in your appetite to an appropriate, weight-sustaining (rather than weight-gaining) level. Also, to the extent that exercise helps increase lean muscle mass, it does increase your daily energy expenditure.
The end.