Yup. Just ‘Why Fat People’. Why do they exist? Why is it so hard for some to lose weight while others have trouble gaining it? Well, quite frankly it’s because the human body is an evolved construct. It evolved under certain circumstances and is best adapted to a certain pattern of activity. It’s been tens of thousands of years since we left that adaptive zone, more or less, but our bodies haven’t changed all that much. Partly this is because unlike other animals, we left that adaptive zone by way of technology instead of changes in our bodies. From about 1.8 million years ago with the rise of Homo ergaster through around 60,000 years ago (the Middle-to-Upper Paleolithic), hominid technology; what little there was, was pretty crude. Instead of taking us beyond the capability of other animals, it merely allowed us to break even with the carnivores. You see, as monkey playing wolf, we didn’t have sharp teeth and claws. Our primitive wooden spears, hand axes, and cutters served as prostheses. But, as Neandertals dwindled and modern humans expanded their range, newer, more advanced tools came to the fore. These novel tools did take us beyond the capabilities of other omnivorous mammals. It made hunting, gathering, virtually everything involved in living easier.
That technology is one of the reasons our bodies haven’t had to change that much. We’re simply less likely to die from things that would kill other animals. A wolf that can’t run fast won’t eat. A man that can’t run fast can just hurl a spear. And, because that technology acts as a prop, it’s allowed us to accrue all sorts of genetic and developmental baggage that makes us in many ways less healthy than we were 40,000 years ago. From the hafted tools our umpteen-great grandfathers used to the computers many of us spend most of our time on, technology has made us fat. What follows is partially science, partially scientific-informed speculation. In other words, while a lot of what I’ll be presenting is fact, a lot is only likely, or merely plausible.
The most important thing to understand about the human body is that it’s an evolved construct. By this I mean it’s a pretty jury-rigged affair when all is said and done. A complex and marvelous mechanism, but shoddily put together nonetheless. Anyone who’s studied Engineering Control Theory would be appalled by the lack of logic of the body’s mechanisms of homeostasis. What I mean by this is that things that are clearly inter-related from an external perspective aren’t necessarily from an internal perspective. The relationship between food intake, energy expenditure, and body composition is one of the most counterintuitive, complex, and just plain retarded systems in the human body. Which might explain why weight control is one of the most difficult things for us to do.
Diet Composition
It would make sense that we eat more food when we expend more energy, food being the primary source of fuel for us. And, that’s a relationship that tends to hold true. The converse would also make sense, that we eat less when we do less. Unfortunately that isn’t quite the case. Our hormonal control systems for appetite and activity are separately maintained, with different ’set points’, different degrees of sensitivity, and different timelines of adaptation. While they do talk to each other, think of them as a long distance relationship rather than a codependent couple.
First, let’s start with food intake. Clearly, how much you eat is a part of the weight equation, but its role is often far overstated. There are a lot of fat people who eat too much. There are also a lot who don’t. And, we all know the rail thin guy or girl who eats 4000 calories a day and can’t put on a single pound. Clearly, food isn’t the be all end all. When I hear about friends who spent weeks, months or even years on one of those super-restrictive 1000-or-fewer calorie diets, I cringe with sympathy. They were misled.
Diet is extremely important to weight loss and maintenance, but not so much the amount as the composition. In fact, low-cal diets can make weight loss harder than if one were to go by a regular 2000 calorie daily regimen. We must ask ourselves what hominids evolved to eat. They are descended from monkeys, which means largely fruit-eating (and occasionally insect, lizard, and egg eating) mammals. Other apes and a couple types of monkeys are known to scavenge and hunt occasionally (1-4% of their diet by weight). So there’s little doubt that hominids were doing at least that. And, there’s very good evidence that hunting and scavenging became a much more important (some would say dominant) aspect of their lives well over one million years ago. Hominids in this respect were probably a lot like the wild social canids (wolves, jackals, etc) in their omnivorous nature. A typical temperate or tropical canid diet can be 40% or more plant product by weight.
And then we can look at intestinal length. The longer the intestine, the more comes from plants. Cows have looong intestines. Monkeys and most apes have shorter ones. Humans are shorter than other primates. Canids are shorter than the above. And cats are shorter than the rest of these guys. In other words, we’re very much in the middle. We’re not carnivores, we’re not frugivores. We’re omnivores. We need a lot of sugars from fruits and other plant parts. And we need a fair amount of protein (from meat, generally).
Which brings us back to the importance of diet composition. Humans are limited not by their fat intake (for the most part), but by their carbohydrate and protein intake. You need carbohydrates to fuel the body. They’re what we’re most efficient and fastest at processing. Fat has more energy per gram, but it’s harder for us to start using it. Just think about that intestine length. We need a lot of sugar in our diet. And we need protein. Although protein can be metabolized as an energy source, mostly it goes to repair, rebuild, and renovate the body. Exercise, metabolism, basically everything we do causes our cell machinery to wear down a bit. That machinery is made up of proteins. Keeping ourselves in top form requires enough protein building blocks coming through our digestive system to undo that damage and a little extra to build bigger and better machinery.
Just about the only thing muscles and the brain run well on are carbs (other parts of the body, like certain organs, do better with fats). Starving your body of them will only destroy your body’s ability to do any work at all. And without protein, you’ll basically find yourself falling apart from the inside out. Some of the stuff I’ve seen and read about what happens in a vegan’s body is nothing short of shocking. Same can be said for those who get most of their calories from meat and none from vegetables.
Old-school hunter gatherer hominids probably burned roughly 3000-4000 calories a day of food. We can estimate that based on what modern hunter gatherers expend. That’s what the human body expects to come through it. Any less than that, and you’re operating in fuel starvation mode. Any more than that and you’re flooding the system with more than it wants. In starvation mode, your body shuts certain things down to conserve energy, and decreases the ability of other parts to exert themselves. In other words, it’s not burning as much as it used to, at least partially negating the effects of caloric reduction.
What’s more, because as I said, activity level and diet don’t perfectly correlate, the super-low calorie diets can shut down so much of your body’s machinery that you actually put on fat because the reduction in energy expenditure has dropped more than the reduction in energy intake. And that’s just talking basal, cell-level, non-activity-dependent expenditure of energy. Of course, caloric reduction also affects one’s ability to undertake activity and thus expend energy, which brings us to our next major topic.
Activity Levels
As I said in the introduction, our activity levels and behavioral energy expenditure are considerably lower than they were in the prehistoric days. I used to get in one to two ‘antisocial’ days when I was in graduate school. On these days I used to strap on a backpack holding roughtly 60lbs of granite and walk 20-25 miles through the streets of London. Beyond giving me a much needed chance to unwind and lose myself in physical exertion, it gave me a taste of what daily life would be like for an early hominid. Based on archaeological remains, we surmise that hominid groups would travel anywhere from 10 to 30 miles in a given period. Furthermore, these finds lead use to believe that they butchered their prey away from their campsites, meaning that, like little old me, they were toting a load for at least part of the journey. I was also a pretty good model because at 5′11″ and about 200lbs I was more or less a walking facsimile of Homo heidelbergensis, the first of the hominids with brain sizes about like ours.
These were 4000 calorie days. But the interesting thing was that not only was I eating a lot on the walking days, I was eating around 3300 on the non-walking days. And not gaining weight. Now, leading a much more sedentary lifestyle with little or no exercise (just like I was 5-6 days out of the week in London), I’m down to 2600-2700 calories a day at a steady 210lbs.
Basal Metabolic Rate
Strange you say? Not especially once you think about it. It all has to do with arousal. I don’t mean the dirty kind, or mental alertness, but the readiness of your muscles and supporting tissues to leap into action. Immediately after blasting through a set on the bench at 100% intensity, you’ll probably notice that your muscles are warmer. Your muscles are metabolizing more sugar, doing more work, and in consequence, releasing more heat as a waste byproduct. Your ability to do work is dependent on the level of this metabolism. The more carbohydrates your muscles are turning over, the more you can lift. Now, getting your muscles primed and ready to do 100% intensity can take a while can’t it? That’s why we warm up. We’re increasing the level of metabolism in our muscles before we actually start doing work with them. But even when we’re just sitting there doing nothing, our muscles and other tissues are metabolizing substrates, burning energy.
This is our basal metabolic rate. Your BMR depends on a number of factors ranging from genetics to diet composition (more sugar, higher BMR, to a point). Another factor it depends on is how warmed up you are when you’re doing nothing at all. You can think of this as priming. Different people have different levels of priming, some of it genetic, some of it having to do with expectation of activity (not activity level). I’m naturally pretty well-primed. My warmup tends to be flexing and shaking a bit and then getting right to it. Which is why with less than an hour of real exercise a week, I still eat close to 3000 calories a day. Other people aren’t quite so lucky, but even they can change their level of priming based on the body’s unconscious expectation of activity. This is the reason I ate more even on my non-walking days back in England than I do now. My body was under the influence of both my genetic priming, and my activity-based priming. My body expected to be worked hard and was maintaining a higher level of readiness, which of course burned more energy. Think standing to attention versus at ease. Both you’re completely stationary, but one’s much easier to maintain than the other.
Conclusion
I’m going to tie all this together with a car analogy. Cars have an air/fuel ratio they like to maintain. For cruising it’s generally about 14.7:1 air/fuel by volume. Less air and you’re lean, more air and you’re rich. Both result in loss of power and efficiency. If we think of dietary composition the same way, too little carbohydrates and too little protein can be just as damaging. It’s important to maintain a good ratio to keep the car operating at a good level of efficiency.
Now, while all cars do best with a single air fuel ratio, the total rate of flow they do best with can be worlds apart. The rate of fuel flow my Mustang has the best fuel efficiency at comes at around 77mph. Whether the rate of fuel flow is higher (faster speed) or lower (slower speed), my Mustang gets worse efficiency. It’s much the same for people, eating less can be just as bad as eating more; under either condition, our ‘rate of fuel flow’ causes us to be in a suboptimal position.
I don’t know how many of my readers have ever drag raced, but there’s a thing you do called power-braking. When you’re at the tree (the lights that tell you when to go), you put your left foot on the brake, pressing down harder than you would at idle. Then with your right you gas it. Depending on the car, the brakes, the horsepower, and the tire, you try to get to the highest RPM’s without either your tires spinning or your car moving. You’re not going anywhere, but you’re burning a lot more fuel than you do at idle. Why? Because when the green hits on the tree, and you let go of the brake, you’re that much further into the efficiency zone of your engine. Priming.
Air/fuel ratio. Fuel flow rate. Idle RPM’s. “Work smarter, not harder”, as Uncle Scrooge from Duck Tales was fond of saying.
