Monday, January 26, 2009

Debunking the Caloric Balance Theory

Note: this post has very little to do with endurance sport, other than that endurance athletes tend to be obsessed with their weight.

Most of us who have ever tried to lose weight subscribe to the basic theory that you just need to burn more calories than you consume, i.e.:

Net Energy Surplus (Deficit) == Calories Eaten - Resting Metabolic Rate - Calories Burned via Exercise

The basic idea is that a pound of fat stores about 3500 calories (454g @ 9 kcal/g = 4086 kcal if you ask me) so if you can cut out 100 kcal/day then you'll lose a pound a month or twelve pounds per year.

But my reading over the last 6-12 months has convinced me that this is not the case.  In fact, it is a rather destructive way of thinking.  This is justified in gory detail by Taubes and is summarized by Thompson but here is a crash course for the uninitiated:

You can lose weight for a short period of time by restricting caloric intake but your metabolism will quickly adjust to this new level of consumption.  Our bodies evolved to withstand a widely variable food supply that was the norm for most of human existence.  And they err on the side of gaining weight as starvation is a much bigger disaster for the organism than obesity.

A more accurate way of thinking about this is:

Net Energy Storage (Use) == Calories Eaten - Burn via Involuntary Activity - Burn via Voluntary Exercise

Taubes also tells us that our fat stores are somewhat self-regulating and whether they are storing or releasing free fatty acids is influenced much more heavily by a collection of local factors than by our energy balance at a macro level.  If your fat stores are not releasing enough free fatty acids to support a reasonable activity level then your body will try to grow those fat stores in order to provide more energy.  So if you have chronically high insulin which is drastically reducing the amount of free fatty acids that your fat stores release then your body will grow those fat stores to compensate -- i.e. if they are releasing at half the "normal" rate then they'll grow to twice the normal size before achieving a new steady state.  So the food that you eat will get stored as fat rather than being used as energy.

So the left side of my second equation above is more of an independent variable than a dependent one.  In fact, the most "dependent" term in the equation -- the one that your body can control the most  -- is the "Burn via Involuntary Activity" term.  Your body has some influence over how much you eat, via hunger and satiety controls...  but the "Burn via Involuntary Activity" accounts for the majority of your energy use.  So let's move it to the left side:

Burn via Involuntary Activity == Calories Eaten - Burn via Voluntary Exercise - Net Energy Storage (Use)

Now that we finally have the right equation, how does your body throttle this "Involuntary" term?

  • If you aren't eating enough, your body will decrease this energy expenditure as much as it can.
  • If you have lots of free fatty acids and/or sugars in your blood then your body will increase this expenditure.  I suspect that free fatty acids are more of a driver here than sugars are, possibly b/c sugars trigger an insulin response which counteracts a lot of the other effects but I am guessing a bit here.
  • These involuntary expenditures include:
    • tapping your foot or twirling a pencil while in meetings/classes/etc. ... I do lots of this!
    • the temperature at which your body runs -- it may tick up or down a few tenths if you have a surplus or a lack of energy to use
    • the number of steps that you walk in a day -- the folks at the 20/20 Lifestyles program have seen this number fluctuate when dieters try to cut calories and track their steps with a pedometer.

The most memorable thing that Taubes said on this subject is that overweight folks don't get fat because they eat to much and skinny folks aren't skinny because they exercise a lot.  Those causes & effects are backwards.  Overweight folks eat too much because they are fat and active folks move around a lot because they are slender.  Now he and I are using "fat" and "slender" a bit generally here to describe the typical endocrine status of these sets of individuals... the "fat" folks' energy storage/use mechanisms are broken and are encouraging the people to eat more, while the "slender" folks' energy stores are giving them lots of energy to use and they're finding ways to use it.  So if you can kick your endocrine system into "slender" mode then you don't have to starve yourself to lose weight.

So there is still an equation but the dependent and independent variables are flip-flopped in the conventional way of thinking.  What do you think?  Does this match your personal experience?  Did I leave out some key details?  Does it sound like I just joined a cult? 

No comments:

Post a Comment