Why do we get fat?

I'm reading Why We Get Fat by Gary Taubes. It's an easy read, science made accessible. It's informative and intelligent. It's well laid out...

And it is entirely validating of my own experience of my body.

The concept of weight loss and weight "management" is built around a principle of physics called the conservation of energy--simply, you can't make something from nothing, so the fat on your body had to come from somewhere. You had to eat it, since we don't absorb calories by osmosis. Either that or you're just not moving around enough to burn off what you eat. Both these things--eating too much or moving too little--are your own fault. They're a visible display of your own failure to manage your body. We accept this principle. We don't question personal responsibility when it comes to weight management.

The problem is, we never took the next step and asked what happens to the calories once they get into the body. We assumed--which is an oversight and makes us look stupid, honestly--that EVERY SINGLE BODY EVER uses calories in the exact same way, in the exact same proportions. If every body did, they it would clearly be a matter of personal fault and easy enough to correct. If you knew that 25% of your intake was going to be used for your brain, 25% would be used for muscles, 25% would be used for essential body functions, and the remaining 25% would be in circulation or fat storage until you ate again, it would be easy to tweak your intake so that you could dictate fat storage. The thing is, it doesn't work that way. That's the message we've all been sold over the last 40-ish years, but that oversimplifies the body and makes fools of us all.

So think about two women, Mary and Jane. Mary and Jane both earn $3,000 a month. Mary and Jane both own houses, and $1,000 a month goes toward their mortgages. This is their essential cost, the cost that must be paid. Mary, however, with her spendthrift ways, regularly spends money on nights out dancing, small weekend trips, books and videos, and new clothes and shoes. Other essential expenses like gas and car payments and insurance are paid, but Mary's primary expenditures are for entertainment. Sometimes there's a little bit left over at the end of the month, but never very much. She puts that away for a rainy day, but feels no qualms about dipping into that money when something new and exciting catches her eye.

Jane, on the other hand, worries about her money all the time. After she pays her mortgage and her essential expenses, she puts everything she can into a strict savings account across town that doesn't have easy access, so she has to go all the way across town to withdraw anything at all. Sometimes she needs new clothes or new shoes, and she plans carefully for these expenses. Her entertainment budget is zero: libraries are free, and they have movies, too. Jane's savings account is already substantial, and saving, for her, is reflexive now.

In the realm of the body, Mary is naturally thin. When she eats her body makes sure that her essential functions are supported, then spends the rest of her calories happily. Every single cell in Mary's body is open for business and eagerly changes those calories into energy. Mary doesn't really notice this because it's just the way she is, but she moves around more often, put more energy into her movements, and is warmer and more awake throughout the day. When she needs more energy for something she takes it right out of her fat stores--that's what it's there for, right?

Jane got the other end of the stick. Her body is heavier and slower. She has generous stores of fat, and yet this stored energy doesn't seem to translate to regular daily energy. She is slower with her movements, and tends to unconsciously shorten them or make them easier. Her hands and feet are always cold, and she always feels just a little bit sleepy. Jane's body likes to store calories for future use, even though she eats the same amount as Mary. Jane also drags herself on a morning walk with her dog every day, but her body is not thin. She burns the same amount of calories in a day at Mary, but her body is not thin like Mary's. Jane's body will make her "entertainment" budget as small as possible, and withdraw from her fat savings on a miserly basis.

This is called nutrient partitioning, and it's gotten little to no consideration in the realm of diet and exercise. Nutrient partitioning, easily, is how your body spends the calories you give it. Some peoples' bodies spend every calorie and save very little. Some peoples' bodies save before they pay any expenses. There has been little discussion of this. We're always told to "eat less and exercise more", as if we've never heard of math and can't understand the simple concepts of addition and subtraction. Being overweight is a failing of intellect, in addition to a failing of character.

And yet...I am not stupid and I am conscientious. But this is what I have consistently experienced in my own body. I have pages and pages of records over the years. I faithfully wrote down all my meals. I laboriously weighed and measured--to the gram--all my foods. I did the math over and over, trying desperately to figure out how many calories I needed and how many I could eat, how it was possible that I was eating X number of calories and exercising for Y minutes and walking at least 5 miles a day and being on my feet all day and still gaining weight. I played with my macronutrient ratios. I also listened to prevailing health and diet "experts", and failed to see the obvious: the higher my carbohydrate intake, the higher my weight and the wider the gap between what I knew I was consuming and the results I expected from the straight math.

Bodies are not simple machines, people. Calories aren't just calories. What your body does with those calories once you digest them is what matters. That's the principle of diet theory that everyone is missing.  Everyone got hung up on the first step--you can't create something from nothing so you must be eating the calories you're storing--and missed the obvious second step: bodies are different, and they're not going to use the same number of calories in the same way.

The question becomes, then, what is happening once those calories are ingested? How do we affect how individual bodies use calories? How do we encourage "saver" bodies to spend freely?