Here’s a great talk by Gary Taubes called “Why We Get Fat.”  I really can’t recommend it enough.  If you don’t have the time or the inclination to read his long, scholarly tome Good Calories, Bad Calories, do yourself a favor and watch this instead.  He sums up the weight gain/loss part of his book in less time than a TV drama, and there are no commercials.

It speaks for itself, but there’s one part I thought I’d expand on.  He’s speaking to a room full of doctors, so he speeds through this bit that might not be so obvious to everyone else.  It’s when he’s talking about the First Law of Thermodynamics, and how people wrongly apply that to weight regulation.  Here’s the law:

ΔE = E_in – E_out

Don’t let the fancy Greek character and subscripts scare you.  All that means is that the change in something’s stored energy (Δ=”Delta”, used in equations to represent the change in something) is equal to the difference between the energy coming into it (E_in) and the energy going out (E_out).  Well, duh, that’s obvious, right?  But scientists like to put the obvious things in formulas and theories so they can be tested (because sometimes obvious things aren’t true) and then used to build up to less obvious theories.

In the context of the human body, that means that the energy you store in a given time period equals the energy you take in (calories from food) minus the energy you give out (exercise, heat, conversion loss, calories remaining in waste, etc).  The two sides of the equation will always match, regardless of whether we know what numbers they actually contain.

When Taubes talks about how there’s no “arrow of causation” there, what he means is that an equals sign just says the two sides are equal.  It doesn’t say which side causes the other, and in fact some outside factor could cause both of them.  But in the realm of weight loss, everyone assumes that the right side of the equation causes the left side, turning the = into a <—.  But that’s the part that isn’t supported by what we know about biology or by our observations (as Taubes shows in many examples).  Yes, the two sides of the equation must be equal, but either or neither can be the cause.

Take a different example—replace energy in the equation with water.

ΔW = W_in – W_out

On any given day, you take in a certain amount of water (W_in) through drinking, eating, and what you soak up in the shower.  You get rid of a certain amount (W_out) through urination, sweat, vapor in your breath,  and so on.  The difference between the two (ΔW) is how much you store.  Now, do you think if you start drinking an extra quart of water a day, that you’ll gradually store more and more water until it starts leaking out of your ears or you swell up like a balloon?  Of course not.  The left side of the equation will force the right side to balance out.  When your body decides it has enough water in storage (based on certain mineral levels and hormones) you’ll urinate more often to get rid of the rest.

And yet, when it comes to weight, we do act like our bodies are simply balloons: that if we take in more energy than we use or expel, our bodies will just happily store it away, with ΔE having no return effect on the right side of the equation at all.

Another analogy:  Your best friend wins the lottery and starts showing up with a gift for you every day.  One day it’s a new TV, the next day a new couch, the next day a collection of all the top-ten albums of the 1980s.  This continues indefinitely.  Now, are you just going to keep squeezing these things into your house until it’s packed to every ceiling and you can’t fit through?  No, you’re going to haul your old couch and TV down to the thrift store to make room.   Maybe you’ll sell some of the gifts, or simply refuse them after a while, but the point is your house won’t just store unlimited amounts unthinkingly.  You’ll control stuff-in and stuff-out to keep it livable.

The human body is a lot more like a house than a bucket.  It has doors and windows that define the ways energy gets into and out of it, and an owner (the metabolism) that decides how much goes both ways.  For example, for a fat molecule from the butter you just ate to be stored in your fat cells, it has to be broken down into its component fatty acids and glycerol to get through the lumen in the gut, then formed back into a triglyceride for transport through the blood, then broken down again to be passed through the wall of the fat cell, then rebuilt again for storage.

Each of these stages requires certain enzymes or other catalysts to be present.  As Taubes explains, the substance needed to break down a triglyceride so it can be passed into a fat cell is stimulated by insulin, which is produced in response to eating carbohydrates.  That’s why Type I diabetics (people who produce no insulin naturally) will waste away to nothing without regular insulin injections: they can’t store any fat, period, no matter how much or what they eat.  There’s nothing at all new or controversial about any of this, by the way.  The only controversial part is using it to draw conclusions about human weight issues.  (Farmers have always known this stuff about animals.  Want to fatten up an animal?  Feed it grain.)

So while your E_in does matter, it matters more what it is than how much of it there is.  If it’s made up of foods that stimulate insulin production which stimulates fat production, you’re going to gain weight because your body will store the extra energy as fat.  If you raise E_in while keeping down your insulin levels (which can be difficult for people with strong insulin resistance, but that’s another 1000-word post), then your body won’t be able to store the energy as fat, so it will balance the equation by raising E_out.  Your metabolism will rise, you”ll start having more energy and feeling like going for walks, you’ll give off more heat, etc.

Anyway, that’s a lot more than I was going to say about it.  Really, just watch it and see for yourself.  It’s given me a nice boost to seriously get back to eating right, thinking, “Why don’t I just do this?  It’s really not that hard, and I like all the foods I should be eating?  Why do I let bland foods like crackers screw me up?”  I know the answer to that one too, but that’s (yet) another 1000-word post.