A couple of years ago, I was talking to a friend who had just built an IKEA bookshelf.

“It looks great,” she told me. “And I barely had any extra parts!”

These days, wise in my old age, when I put together furniture, I tend to read the instructions through once or twice first, then follow them to the letter. And, invariably, all of the included parts end up in the finished product.

Simply put, manufacturers are controlling costs to the penny, and they don’t just throw in a few extra bolts for good measure.

Evolution works the same way. Developing biological structures in a growing body is extremely physically costly. Nature is parsimonious. So it would be surprising to discover that we have major physiological structures ‘by mistake’.

Indeed, over the last few decades, we’ve increasingly discovered that organs we once believed were vestigial – evolutionary ‘leftovers’ – actually serve important functions that we simply hadn’t yet discovered.

Consider the appendix, which paleontologist Alfred Romer once joked served primarily “to support the surgical profession.” In the last fifteen years, we’ve discovered that it’s crucial in early childhood, aiding in the maturation of B lymphocytes and the production of antibodies. And a growing group of scientists has suggested it also serves as backup reservoir of good gut microbes, so that we can healthily ‘reboot’ after illness. Individuals without an appendix, for example, are four times more likely to suffer from C. diff. colitis, a bowel irritation caused by the overgrowth of bad bacteria.

As a result, I’m particularly dismayed by the number of surgical interventions that ‘fix’ problems by simply disposing of structures that are the current source of problems.

Consider gastric bypass, the current state of the art in bariatric medicine. To help people lose weight, a bypass reduces the size of the stomach, to decrease appetite, and then routes the vast majority of the food around the large intestine entirely, to keep people from absorbing the majority of the food they eat. Problematically, different parts of your intestines absorb different kinds of food, so that ‘reduced absorption’ caused by arbitrarily skipping parts is actually a short path to unbalanced malnutrition. And the skipped gut serves all kinds of immune and neurological functions beyond simple digestion, which we lose when we indiscriminately cut it out of the picture. Further, dumping food into later parts of the intestine in a less-digested state causes additional problems, because those later parts weren’t designed to function properly with that kind of undigested input.

You can argue here as to whether the doubtless deleterious effects of wrecking your digestive system is outweighed by the more pressing disaster of morbid obesity. But you can also lose weight by cutting off your legs, yet fewer medical centers have popped up around that idea, mainly because the missing legs are a more immediate problem than those caused over time by a bypass.

Similarly, I’ve talked to a number of orthopedists who proudly ‘treat’ plantar fasciitis surgically by cutting the plantar fascia. Your plantar fascia is tight and painful? We’ll just snip that thing, and everything will be great! Except, obviously, it won’t. Your plantar fascia plays an important role in the structure of your foot, and in the way you stand, walk and run. With yours missing, you’ve created a slew of new problems. Whatever underlying disfunction caused the plantar fasciitis hasn’t disappeared; it will just slowly start wrecking a different portion of your body, further up the biomechanical chain.

You can see this clearly in surgeries like total knee replacement. Your knee is meant to bend in a straight line, but if you spend enough years putting weird torque into the system due to wonky movement patterns, you’ll eventually wear through the cartilage that’s meant to serve as side-rails, rather than as a primary support surface. After that, you’ll start to grind away the bone, which really hurts. So an orthopedist can solve the problem by removing your knee completely, and replacing it with a metal version that’s simply too strong for you to torque it in a damaging way. Problem solved! Except, of course, it hasn’t been solved here, too. Your wonky movement patterns persist, but because you can no longer get play in the system at the knee, your body start compensating at the hip or low-back instead. Indeed, after total knee replacement, the odds of needing surgical intervention at the hip or low-back skyrockets. But don’t worry, we can also fix those. We can replace your hip with a metal version, too. Or, if the bendy parts of your spine aren’t moving the way they should, we can just fuse them together so they can’t move any more. We’re great at this!

All of which is to say: your body is a hugely complicated system, which operates holistically in ways that we’re just beginning to understand. Giving real thought and research to how different inputs change the output of that system is probably a smart route to finding solutions that are helpful in the long-term. But removing ‘extra parts’, and then not expecting that to cause all kinds of new and unexpected problems seems a rather myopic way to go.

Yesterday, I wrote that the basic ‘thermodynamic’ equation of weight loss (calories in – calories out = net calories) glosses over a lot of important information, mainly by obscuring the definitions of ‘calories’, ‘in’, and ‘out’.

So let’s clear things up a bit, starting today with calories themselves.

When we discuss “calories” in food, we actually mean “kilocalories”, as nutritional calories are based on 1000 thermodynamic calories. Outside of the nutritional world, a kilocalorie is a well-defined measure of energy: the amount of heat required to increase the temperature of one kilogram of water by one degree celsius at a pressure of one atmosphere (i.e., at ground level).

We test calories in food using what’s called a ‘bomb calorimeter’. Basically, it’s a device for blowing up food, and then seeing how hot the explosion makes surrounding water. To operate a bomb calorimeter, you take a small amount of food, and put it into a metal canister filled with pure oxygen, with a fuse that extends out to an electrical ignition. Then you submerge the metal canister, floating it in a kilogram of water. You carefully check the temperature of the water at the start. Then you hit the ignition, and the food explodes. As it does, the heat from the burning food begins to raise the water temperature. By tracking how much the temperature increases at its peak, how many degrees celsius the water temperature rises from the starting point, you’ve got the number of kilocalories in the food you just blew up.

Odds are, you aren’t a biologist. But you’re likely still aware that this isn’t really what happens inside of your body. You don’t walk around with a series of explosions detonating in your stomach all day long. (However, insert fart joke here.)

Tomorrow, when we look at ‘calories in’, we’ll try to get a better sense of what your body actually does to extract the energy from food. But before then, there are a few even more fundamental problems.

Towards the end of the 19th century, Wilbur Olin Atwater, a scientist at Wesleyan University, set out to understand the connection between heat calories (the kind you measure when blowing up food) and nutritional calories (the metabolisable energy your body derives from that food), through a series of experiments.

Atwater tested the heat calories in a wide variety of foods. And then he tested the heat calories in the feces of people who had eaten those same foods, to determine ‘apparent digestibility’, the percentage of the calories absorbed by the body rather than excreted.

The results of those experiments are the “Atwater factors”, the well-known idea that a gram of fat contains 9 calories, while a gram of protein or a gram of carbohydrate each contain 4 calories.

Most people don’t realize, however, that those numbers are averages. Not all fats, proteins and carbohydrates have the same amount of heat calories per gram. Similarly, not all fats, proteins and carbohydrates have the same apparent digestibility. So Atwater devised weighted values for the gross heat of each macronutrient, based on what he thought to be their prevalence in the standard diet at the time.

Similarly, Atwater first tested the apparent digestibility of individual foods. Then he started combining foods together, the way we do when we actually eat things. At that point, however, the numbers started to muddy up. Unfazed, Atwater simply came up with ‘adjustments’ that he hoped might account for the discrepancies in the mixed diet numbers.

When Atwater was doing his experiments, the best-selling Fannie Farmer cookbook was just introducing newfangled kitchen technology like the measuring cup and spoon. The cookbook featured perennial favorites of the time, like turnip croquettes, tomato cream toast, and Washington-style terrapin (turtle served in white sauce with its liver, small intestine, and “any turtle eggs”).

In other words, the ‘standard diet’ on which Atwater based his average computations is more than a bit different from what most of us eat today.

Similarly, Atwater’s ‘adjustments’ to account for mixing foods are difficult to justify in retrospect as anything other than liberal massages of the raw data to better align with his intended conclusions.

So even before we begin to look at how our bodies digest and assimilate foods, it’s clear that perhaps calorie math – which has the reassuring appearance of incontrovertible science – isn’t quite as objective and accurate as we might hope.

Indeed, calorie math doesn’t really take into account the difference between, say, a gram of carbohydrates from a strawberry and a gram of carbohydrates from a pear, or what happens when we eat them together, along with some sugar and cream. (Which, as an aside, sounds delicious.)

Further, it doesn’t even take into account the substantial differences from one strawberry to the next. A huge number of factors in the life of each strawberry can affect its nutritional content. At what time of the year was the strawberry planted and picked? How often was it watered, and how much? Was it fertilized? How much direct sunlight did it get, and how close was its nearest strawberry-plant neighbor? As a result of these and countless other questions, any given strawberry might have different amounts of fructose, glucose, sucrose, soluble and insoluble fiber, and micronutrients than the next.

The result of all of this is that we can’t even answer a very basic question, like “how many nutritional calories are in a cup of strawberries?” We have pretty much no idea.

So, calories. Not really what they’re cracked up to be.

But wait, it gets worse! Tune in for Part III, to learn why, even if we knew how many nutritional calories were actually in that specific cup of strawberries you’re holding, it still has only a small bearing on what happens once you actually put them into your mouth.

A lot of nutritionists, diet book authors, and health experts love to point out that losing (or gaining) weight is a simple matter of thermodynamics: calories in – calories out = net calories. If net calories are positive, you gain weight; if net calories are negative, you lose it.

And, at a very high level, that math is correct. But, like with most real-world processes distilled to simple models, it’s also missing a whole lot of important detail.

In short, there are three main problems with the calories in / calories out formula: we don’t accurately define ‘in’, we don’t accurately define ’out’, and we don’t accurately define ‘calories’. Other than that, it works great.

Over the next few days, I’ll be unpacking each of those three definitions in separate posts, to see if we can better understand how people lose and gain weight. As you might expect, the reality is a bit more complicated than a six word equation. And the devil – as well as our salvation – is all in the details.

A month back, I mentioned that I’d been following SEALFIT, an over-the-top approach to CrossFit-esque workout programming targeted at the military special operations crowd, for the past four or five months.

In a lot of ways, it was a great experience. First and foremost, I learned that I could push myself through vastly harder and longer workouts than I would have expected. Several times a week, halfway into a workout, I’d realize there was just no way I could make it to the end. But then I’d put one foot in front of the other, and inch my way through. And, somehow, I managed to finish every single one.

At the same time, the volume was insane, sometimes involving hours a day of workouts that beat me into the ground, one after another. Paired with the stresses and time commitments of real life, it proved to be too much. I got sick, and then got sick again. My resting pulse climbed and my heart rate variability plummeted. I had clearly veered deep into overtraining territory.

So, a few weeks ago, I moved laterally to try out the programming from Power Speed Endurance (née CrossFit Endurance). While it’s similarly biased towards running (and therefore in line with my 2016 goal to become a less terrible runner), and still includes two-a-day workouts twice a week, it also follows sensible progressions, includes a lot of pre-hab and mobility work, and generally seems like something you could do for an extended period of time without a death-wish.

In parallel, I’ve been writing a bunch of programming through Composite, and at some point it seems inevitable that I’ll circle around to eat my dog food. But, for the moment, I’m enjoying testing out another fitness guru’s best thinking. If you’re looking for some smart, challenging workouts (and especially if you’re a runner, cyclist, or triathlete), it’s worth checking out.