When it comes to the subject of losing weight—more specifically, reducing excess fat stores in the body—it’s fairly common to come across somebody who puts it like this:

It’s just calories in versus calories out. Thermodynamics says that if you take in more calories than you burn, you’ll store them as fat. If you take in fewer, you’ll burn fat. So weight loss is very simple: just burn more calories than you take in. That’s it. Anything else is just people trying to kid themselves that here’s a magic bullet.

This represents a confusion one sees in many fields: making no distinction between the cause of something and the mechanism of how the cause makes it happen. It is quite true that when somebody stores fat in their body they require energy to make the fat and they can’t also burn that energy and therefore the amount of energy they took in was higher than the amount of energy which they burned. No one, anywhere, disputes this. It’s also entirely uninteresting to the subject of fat gain or loss in people with excess fat.

(NOTE: when talking about healthy people—typically lean athletes—regulating what little fat they have, this simplification is probably accurate. This post is not talking about how a body builder can force his body to levels of fat which are dangerously low, or how an athlete can cut to a lower weight class. Those will almost certainly have to be achieved by simple calorie restriction because they are manipulating a healthy body into going outside of the homeostasis it wants to maintain for optimal health).

The question which is actually interesting to the subject of fat gain or loss is why the body stores energy as fat. And this is where the people who love to talk about calories-in-calories-out show their reductionist colors. Tthey will tell you that since fat cells are energy storage, if you take in more calories than you burn, you will necessarily store them as fat. But they give no reason for this, while there are excellent reasons to doubt it.

The reason to doubt that extra calories eaten can only go to fat is that the human metabolism is a highly variable thing. Though I should clarify what I mean here because by “metabolism” some people mean “resting metabolism”, while I mean “total metabolism”. Our bodies spend calories on a lot of things—walking, talking, maintaining our temperature, repairing our bodies, and other things. Very few of these things are fixed costs. One possible reaction to being in a cold environment is moving more or just burning energy for heat. Another is feeling cold and putting on a sweater. Those do not use the same number of calories over the course of an hour.

Let’s consider a very analogous system: finances.

If a person makes an additional $1000 per month, it is possible that his bank account will grow by $1000/month. It is also possible that he will start eating at expensive restaurants, and his bank account won’t change at all. On the flip side, a person whose income doesn’t change can decide to stop eating out and can grow his bank account with no additional income, merely by cutting expenses. And could do both: he could decide his bank account isn’t nearly large enough, work a second job to bring in an extra $1000, move to a tiny, unheated apartment, and eat nothing but porridge for his meals so that his bank account swells rapidly.

It’s that last part that’s most interesting to the moment, because it’s what seems to be the case in people who are, shall we say, famine resistant. Because there’s a really fascinating question about people carrying excess fat which is rarely asked: why do they get hungry?

Seriously, why is it that a person with excess fat feels hungry when he has plenty of energy at his ready disposal? That’s not how the body normally works. The human body, when working correctly, tries to maintain a homeostasis. Granted, it’s a homeostasis with more fat than a bodybuilder would like, but the body tends to regulate hunger on the basis of energy availability. Or in other words, normal people usually stop being hungry when their calories in is roughly equal to their calories out.

At this point, a word is necessary about what we might call the balloon theory of hunger. Basically, it is the model of hunger where the stomach is a balloon with pressure sensors and hunger is merely the pressure sensors detecting whether there’s still room in the stomach to fit something without literally bursting it.

There is some minor truth to this, in that the stomach does in fact have sensors in it which detect the degree to which it is stretched, but a few years of living as a human being should be sufficient to show this model as the rubbish that it is. Consider a few counter-examples:

1. Desert. A person can eat until “they’re so stuffed they can’t eat another bite” then the moment desert comes out they can somehow fit enough additional food to fill a grapefruit.
2. Exercise makes people hungry. Starting a new exercise routine can make one feel ravenously hungry for days. Exercise does not drastically increase the size of someone’s stomach in the first few days.
3. Teenage boys can out-eat their parents combined. I did it often as a teenage boy. (I was on the rowing team in high school and relatively lean, too.) Teenage boys do not have stomachs which are larger than their mother’s and father’s stomach’s combined.
4. Tests show that a stomach can stretch to around the size of an entire human torso before bursting from pressure. They’re incredibly expandable.
5. People who win hot-dog eating contests do not ordinarily eat that much food to feel full.

In short, the theory that being hungry is entirely, or even primarily, about whether your stomach is full is nonsense.

There is also the always-hungry model, which tends to involve some pretend evolutionary biology about humans having evolved in circumstances of constant famine and so we are always hungry in order to pack on as much fat as possible for the next famine which we know is right around the corner.

The main problem with this is that it directly contradicts experience. Americans live in an environment with truly enormous food surpluses always available, and there are plenty of not-fat people who eat until they are not hungry and who nevertheless do not eat the 10,000+ calories that they easily could and this model predicts.

In short, a little bit of experience shows that human beings are not normally ravenous eating machines consuming every calorie that they can get their mouths on.

With these models of human hunger out of the way, the question then comes up and is very pressing: why do fat people get hungry?

It is not the purpose of this post to give the answer to this question. Chief among the reasons why is that there are almost certainly many answers to this question; people’s energy regulation can get screwed up for a variety of unrelated reasons. It is only the purpose to highlight how important finding an answer to this question is for a person who wants to lose excess fat.

(So as to not completely shirk the question, I think that one of the most common is excessive fructose consumption causing insulin insensitivity in the liver, which cascades into general insulin insensitivity, which then disrupts energy regulation, though even that is probably an over-simplification since in general nothing in biology involves just a single hormone. This model, however, at least corresponds well to my own experience of when I gain and lose weight.)

There’s a really good metaphor for the issue in Tom Naughton’s post Toilet Humor: The How vs. Why of Getting Fat. I’m going to give a variant of this metaphor to keep things more pleasant: the kitchen sink.

Suppose that your sink is clogged and filling up with water and about to overflow. It is entirely true that the problem, in an acute sense, is that there is more water going into the sink than coming out of it. If one applied the standard dietary advice to a clogged sink, you would just drastically reduce the flow of water into the sink until the sink was empty.

And it will work if you do that. Cut off the water, and the sink will eventually not be full of water. Evaporation, if nothing else, will see to that.

There’s just one problem: you have the sink for a reason, and that reason is not merely to keep it empty. You want the sink to do work. And the water-in-water-out approach of just cutting off the water in means that your sink can’t do its job. The correct solution to a clogged sink is not to stop washing your dishes. It’s to find out why it’s clogged and clear the clog. Maybe the drain strainer is full. Maybe the pipe is clogged later on. Fixing the problem depends on what the problem is, and there isn’t one problem. But whatever the obstruction in the drain, that’s what you need to fix so that the sink can do its job.

Similarly, a human being almost certainly has things to do besides sitting around not being fat. Many of us are parents. Some of us have jobs. A few of us have friends. Whatever it is, we have more to do than just sitting around not being fat. Just cutting off our food without fixing why we’re hungry when we’ve got excess fat is like just cutting off the water to the sink. Whatever you’ve got to get done in life, you’re going to do a bad job.

Further, people who are constantly hungry tend to be irritable, short-tempered, and lethargic. Even if they manage to fulfill their primary responsibilities well (and they’re probably only doing it passably), they’re going to make life less pleasant for everyone around them. I once had a housemate who was doing a calorie-restricted cut, and I was nearly at the point of begging him to stop because he was just so unpleasant to be around during it.

Interestingly, you can see the same sort of indifference-to-function in sports-medicine vs. regular medicine. If an athlete has a problem where something really hurts when he uses it, the conventional medicine approach is to just stop playing the sport and (I’m exaggerating) get months of bed rest. People into sports medicine know that this is hyper-focusing on a mechanism—in this case, rest—while ignoring that the person is a human being with a life. Sports medicine tries very hard to figure out how to restore athletes to normal function in the context of still living life as an athlete and not considering being wheelchair-bound-but-alive to be an equivalent outcome.

So, in conclusion, the real question when it comes to someone who wants to lose excess fat is not how to get rid of excess fat. It’s how to fix the fact that they’re hungry when they shouldn’t be. If you fix that, then the person will certainly lose excess fat—people who aren’t hungry don’t eat as many calories. But they’ll do it while still being a functional human being.

In short: one should treat the problem, not the symptom. To do that, one must first identify the problem.