On the Subject of Weight Loss
This is a little outside the realm of my usual topics, but it’s come up enough times now in conversations that I want to write about it.
There is a lot of heated debate right now about obesity: how it affects health, whether it is the result of moral failings, who should have the right to comment on it or define it, what to do about it, and on and on.
I am not a healthcare professional or a professional biologist. At this time, I am relying on my memory for much of this information rather than doing due diligence and looking up the relevant studies, although I certainly encourage others to do so. All numbers given in this essay are for the purpose of illustration only: they are not based on any actual data. Also, please excuse my tendency to anthropomorphise biological processes: your internal components obviously don’t actually “think” or “want” things, but it’s a convenient way to describe what occurs.
All that being said, let’s see if I can address one of the most common misconceptions about calorie intake and body weight: the idea that there is a direct, linear relationship between these two things. There is not. I commonly run across the argument that anyone can lose weight by reducing the amount of calories they ingest. Some people claim that exercise is also necessary, but the general point always comes down to the idea that fat is caused and maintained by eating more calories than one uses, and can be reduced by reversing this behavior. But biological systems are a lot more complicated than that.
First, it is a mistake to consider calories fungible (or equal or interchangeable). Our bodies may process the same number of calories very differently depending on the form of those calories, which is why we have terms like “empty calories” (calories that don’t have much nutritional value) and “good” or “bad” carbs and fats (based on how we digest them and what their health effects tend to be).
More importantly, though, there’s also an incorrect understanding of what it means to need a certain number of calories per day. I often hear people say things along the lines of “Well, just figure out how many calories you use per day and don’t eat more than that.”
What do we count as “using” calories? We don’t just burn calories when we engage in deliberate physical activities. Energy consumption is involved in everything we do– breathing, moving, thinking, growing. We use calories to repair injuries, replace damaged cells, increase muscle mass, go for a walk, digest our food, maintain our fat reserves, and to perform all mental activity, from deliberate problem-solving to emotional regulation to sensory processing. And it’s not easy to determine how many calories are needed for optimal performance of all these tasks.
Your body doesn’t necessarily prioritize calorie allocation in the order that you’d like. In fact, one of the first things that gets cut back in a calorie shortage is brain-power. Your brain is a massive energy-hog, and evolutionarily speaking, we don’t need to spend much time on math and science and history and office politics and romantic relationships and social activism and keeping our temper when our boss is being a twit. We can pretty much get away with: Find food, find mate, don’t get eaten.
So when you have fewer calories to work with, the cutbacks start in the brain. You may have noticed this personally. When we’re hungry, we’re often grouchy and easily frustrated and have a harder time focusing and thinking clearly. But don’t take your own experience’s word for it. There’s a lot of research evidence on this– comparing test scores of students who have and haven’t skipped breakfast, impulse control in hungry versus sated people, and so on.
Your body has its own internal settings– what temperature it wants to be, how much sleep it needs, and so on. And your body is willing to put a lot of resources towards keeping things the way they are. These settings include an approximate set point for weight, which is why there are people who remain skinny regardless of consumption and people who remain fat even with healthy diets and high activity levels. And why medications, illness, age, and other factors can drastically alter a person’s weight even if the person’s diet and habits remain fairly constant. Lasting weight change requires changing your body’s set point, and some bodies make this change more easily than others.
Generally speaking, it is hard to get your body to change the set point to a lower one… and relatively easy to get your body convinced that it should have more fat reserves. Excess consumption obviously has this effect– the body says “hey, let’s store some of this extra for later!.” However, cutting back dramatically on calories can also increase weight, because your body thinks “huh– I’m getting fewer calories than usual. We may be preparing for a drought, lean harvest, or other time of scarcity, and we don’t know how long it will last. We’d better save up as much as possible now.” Your body then boosts your hunger signals and again starts cutting calories from other areas of functioning. This is one reason why drastic calorie restriction diets do far more harm than good.
As I understand it, body weight maintenance is highly prioritized by our physiology– pretty much right after critical systems like circulation and digestion. And I suspect one of the reasons exercise is so important to weight-loss is not just how many calories it burns, but that muscle-building is one of the few causes your body ranks highly enough to actually prioritize over maintaining fat reserves.
Let’s look at a couple fictional scenarios illustrating the ramifications of all this. Imagine you consume an average of 2000 calories per day (the numbers and proportions here are completely fictional). Let’s say you spend 300 of those calories (about 1/7) on basic internal maintenance tasks, including maintaining your current body weight. Maybe 1000 calories go to mental activity, and the remaining 700 to physical activity.
You want to lose some weight, so you cut down to 1500 calories daily. There are several possibilities for how your body can react.
1) Your body keeps the ratios the same: 1/7 to keeping your body as it is, about half your calories for the brain, slightly less for voluntary movement. This isn’t too bad– you’ll lose weight slowly and have to put up with being a bit more tired than usual for a while.
2) Your body keeps putting those 300 calories per day towards homeostasis (including body weight), leaving you with only 1200 calories to be split between physical and mental activity rather than 1700.
3) Your body decides you may be facing a calorie shortage and increases the percentage of calories it turns into body weight, at an even higher cost to other functions.
4) Ideally, your body would trim fat without making any significant cutbacks in other areas, resulting in weight loss with no negative side effects. This is certainly possible, but it is far from being the only, or even the most likely, result of cutting calories.
In short, reducing intake alone is a pretty poor gamble to take if you’re trying to lose weight. The real trick is to get your body to change its ideas about how to allot your calories, and that’s a lot more complicated. Excercise can help, but isn’t necessarily sufficient. A more complete answer involves eating more nutritious food, increasing both physical and mental activity levels, and a bunch of other subtle epigentic factors that we’re far from understanding. We know that stress and general happiness have a huge impact, and so do sleep schedules. And there’s compelling evidence that eating a diet closer to the traditional diet for wherever your people came from can be a huge help regardless of calorie count. And so on and so forth.
It’s even harder to study all this than it sounds, since people who make significant body weight changes often have many of these factors involved, and the factors themselves can interact. When people get into exciting new relationships or more high-pressure jobs or experience other major life events, their stress levels change, their priorities change, their personal habits change, their mental health changes, other medical factors change… and it’s nearly impossible to untangle the order and magnitude of all these changes. Similar factors are involved in quitting smoking and other such things that require a fair bit of wrestling against the instinctual reactions of one’s own mind/body. So chances are good that the person who just “up and decided to lose weight one day” had life circumstances that played into making that decision, being able to stick to all the lifestyle changes necessary, and having their own biology respond in the way they wanted.
This certainly isn’t to discourage anyone who wants to lose weight from trying; rather, people who want to lose weight and have failed with only diet and exercise may simply need to take a more holistic approach that prioritizes improving general wellbeing rather than merely reducing waist size. But it’s also important to acknowledge that we are very complicated systems, both physically and mentally, and some of the factors that affect our systems are generally beyond our awareness, much less our control.