Adaptive Thermogenesis - WHY?

[Daves_Not_Here]

Following up our previous discussion of Adaptive Thermogenesis:  An NCBI published study asserted that "a formerly obese individual will require ~300–400 fewer calories per day to maintain the same body weight and physical activity level as a never-obese individual of the same body weight and composition"   This is consistent with the experiences of Biggest Loser contestants who found their metabolisms were lowered for years after their large weight losses.

So, the natural question for me is WHY?  What is it about a large weight loss that leads to an abnormally low metabolic rate?  What is the mechanism for it?

If we deconstruct a weight loss, it arises from a sustained calorie deficit -- more calories are burned than eaten.  The deficit has two components: (1) increased energy expenditure, and/or (2) reduced food consumption.  So, which of these tends to lower metabolism more?

You could argue (as many do) that eating less tends to trigger a starvation response, wherein metabolism is lowered to conserve energy during famine (but, you could counter that such a response would be maladaptive, as you need more energy available to hunt and kill the next meal).  Or, you could argue that more exercise tends to increase your fitness, which means you burn less energy to perform exercise activity - why wouldn't that also lower how much energy you need to sleep and sit around all day?  I'm drawn more to the second hypothesis.

Dr's. Volek and Phinney cite 4 studies that found cardio exercise reduces metabolism in The Art and Science of Low Carbohydrate Performance.  Starting on p. 39, they devote 3 pages to Side Bar: The Uncomfortable Truth About Endurance Exercise, Resting Energy Expenditure, and Weight Loss and assert that the studies indicate that "when overweight humans do more than one hour of endurance exercise daily, resting metabolism on average declines between 5% and 15%".  More provocatively, the decline in metabolism occurred even when the subjects had not lost weight. 

They conclude by acknowledging the value of endurance exercise for health and fitness, but challenge the notion that it is effective for weight loss.  And on p. 26 they find that resistance training maximizes fat loss while increasing lean body mass.

[Dominique]

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@Daves_Not_Herewrote:

So, the natural question for me is WHY?  What is it about a large weight loss that leads to an abnormally low metabolic rate?  What is the mechanism for it?

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I think it’s a survival mechanism: the human body hasn’t had the opportunity to evolve and realize people who live in rich countries are surrounded by an abondance of food at all times. From what it knows, your large weight loss may be the result of prolonged famine. Now you’ve signaled food is no longer in short supply, but based on the precautionary principle, it wants to save energy (hence the lower metabolic rate), just in case there’s a new bout of famine going to start soon. The ultimate aim of living creatures is to survive and be able to reproduce, not to show off their six-pack abs at the beach.

[WavyDavey]

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@Daves_Not_Herewrote:
 

Dr's. Volek and Phinney cite 4 studies that found cardio exercise reduces metabolism in The Art and Science of Low Carbohydrate Performance.  Starting on p. 39, they devote 3 pages to Side Bar: The Uncomfortable Truth About Endurance Exercise, Resting Energy Expenditure, and Weight Loss and assert that the studies indicate that "when overweight humans do more than one hour of endurance exercise daily, resting metabolism on average declines between 5% and 15%".  More provocatively, the decline in metabolism occurred even when the subjects had not lost weight. 

They conclude by acknowledging the value of endurance exercise for health and fitness, but challenge the notion that it is effective for weight loss.  And on p. 26 they find that resistance training maximizes fat loss while increasing lean body mass.

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That's very interesting because it's exactly in line with personal experience. Endurance work is great for burning calories, but in trying to effect a metabolic change, resistance/strength training provided me a larger boost to the metabolic system. I say this because with strength training I've had to increase my calories in just to maintain weight.  Kind of of the opposite phenomenon of the biggest loser phenomena,

Studies cited by Dr. Jonathan Sullivan indicate that the metabolic adaptation from resistance training is very long-lived also.  He refers to this as adding deposits to our "physiological 401K".

I think it's easier to overlook the importance of metabolism with a simplistic calories in/out viewpoint. As in a car, the engine's efficiency is as important as the right fuel.

[Daves_Not_Here]

@Dominique wrote:

@Daves_Not_Herewrote:

So, the natural question for me is WHY?  What is it about a large weight loss that leads to an abnormally low metabolic rate?  What is the mechanism for it?

I think it’s a survival mechanism: the human body hasn’t had the opportunity to evolve and realize people who live in rich countries are surrounded by an abondance of food at all times. From what it knows, your large weight loss may be the result of prolonged famine. Now you’ve signaled food is no longer in short supply, but based on the precautionary principle, it wants to save energy (hence the lower metabolic rate), just in case there’s a new bout of famine going to start soon. The ultimate aim of living creatures is to survive and be able to reproduce, not to show off their six-pack abs at the beach.

@Dominique -- Thanks - I'm familiar with (and tried to paraphrase) that line of reasoning (which I will call the "Energy Conservation during Famine" theory), but one point of my post is to explore an alternative explanation (Reduced Energy due to Fitness).  

If we are to conserve energy during famine, what is the mechanism by which metabolism is down-regulated?  Does our thyroid modulate T3 and T4 in response, and is NEAT reduced as a result?  And what of the observation that during fasting, our metabolisms speed up, presumably to enable more vigorous hunting?

I'm intrigued by the alternative hypothesis because it makes more sense to me -- if I now burn about half the calories during a 4 hour bike ride compared to when I was out of shape, it seems reasonable that I will also burn less calories during the remaining 20 hours of the day.  

I believe the alternative theory better aligns with the struggles reported in this forum:  people are working out for over an hour per day and cannot lose more weight after an initial period of loss (which I'm thinking is an initial period of conditioning).

[Mukluk4]

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@Daves_Not_Herewrote:

I'm intrigued by the alternative hypothesis because it makes more sense to me -- if I now burn about half the calories during a 4 hour bike ride compared to when I was out of shape, it seems reasonable that I will also burn less calories during the remaining 20 hours of the day.  

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"In Shape" and "Overweight" are not interchangeable measurements and you can very well be both.  I have a 36.9 BMI (super fat category), better than normal Cholesterol, Blood Pressure, and resting heart rate and a 36 inch waist.  Basically everything except the number on the scale says I'm in the best shape of my life. 

At one point, I was playing full court basketball with a 42.2 BMI (320ish pounds).  I wanted to die afterwards, but I could do it.  My current fatass, can outrun average to athletic high school and college kids and run circles around guys my age within normal to overweight BMI.  

Just setting those standards, it's pretty easy to see that my body has become efficient enough that I have to go through some major extremes to cut anymore weight and I don't ever foresee a future where I would land at a normal BMI range as I'd have to drop at least 70 pounds to get there.

[Daves_Not_Here]

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@Mukluk4wrote:

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"In Shape" and "Overweight" are not interchangeable measurements and you can very well be both. 

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@Mukluk4 - agreed.  A year ago, I was exercising regularly, had relatively high aerobic and anaerobic fitness, but was obese.  I was blobbing up like Richard Simmons without the lisp.  However, I had low HDL, high A1c, and was headed towards diabetes, so I have a number of reasons now to be thankful.

[Dominique]

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@Mukluk4 wrote:

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"In Shape" and "Overweight" are not interchangeable measurements and you can very well be both.  I have a 36.9 BMI (super fat category), better than normal Cholesterol, Blood Pressure, and resting heart rate and a 36 inch waist.  Basically everything except the number on the scale says I'm in the best shape of my life. 

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One thing to consider is age: you may indeed be heavy and in good shape with flawless health markers when you are in your 20’s and 30’s. However, some risk factors are cumulative and may manifest over time (once you start getting in your 50’s or 60’s). A heavier weight puts more stress on your joints, e.g. knees and hips (especially if you are into sports like basketball, which require a lot of jumping on a hard surface). Larger tissue masses also require more blood to be pumped through them, putting more stress on the heart. I heard an interesting analogy about intra-species lifespan variation: within the same species, smaller breeds tend to live longer than larger ones. Great Danes seldom live past 10 years, whereas it’s not uncommon for Chihuahuas to live past 20. 

[Mukluk4]

A heavier weight puts more stress on your joints, e.g. knees and hips (especially if you are into sports like basketball, which require a lot of jumping on a hard surface). Larger tissue masses also require more blood to be pumped through them, putting more stress on the heart. 

Agree wholeheartedly, I've had bad knees since my high school years and knee replacement will happen in my future.  My goal is to keep my activity lifestyle going until I'm 50 and everything after that is bonus.

My biggest fear is blowing a knee and my wife says I'm done if that were to ever happen.  As such, I get my knees checked out every fall after the pavement ball is over and before the gym ball begins to try to catch anything preemptively.