This one is for all you big eaters. I've always been a big eater, at least I know I have been over the last ten years or so since I started paying attention to this sort of thing. But I at least know that I was a big eater before I went paleo, and I still am now. People who are around my size just don't eat as much food as I do. This has led to the usual jokes: "You must have a tapeworm" (tapeworms can actually decrease your appetite, I've read); or "where does it all go"; or "it's amazing that you're so slim." And it's true, I don't ever gain weight. (I lost my late-20s belly fat when I went paleo, but before going paleo I also always stayed at a constant weight.) I do exercise, but not excessively: weights a couple times a week, cardio once a week, sprints once a week, walking, etc. But even when I don't exercise, for days and days, I still eat a huge amount.
I always assumed I had a big appetite because I carry a fair amount of muscle on my body (BMI 24). And I always thought that muscle was metabolically expensive, even when you're not exercising -- simply keeping it on your body consumes a lot of calories. But I was just reading through this great post from Dr. Mike Eades, "Are we meat eaters or vegetarians? Part II," and it got me thinking. The main concern of his post is to explain the classic article by Aiello and Wheeler, "The Expensive-Tissue Hypothesis," in which the authors show that human beings, compared to other primates, have disproportionately large brains and disproportionately small guts -- which one can take as good evidence for our meat-eating past. That topic is really interesting, of course. But one paragraph from Dr. Mike's post got me onto these new reflections of mine:
The authors of the ETH [The Expensive-Tissue Hypothesis] set out to look at the metabolic rates of the various organs. By a diligent search of the literature, they found that along with the brain, the heart, the kidneys, the liver and the gastro-intestinal tract account for the vast majority of the total BMR. They dubbed these organs as ‘expensive tissues’ because they consume a large amount of energy as compared to their size. (Surprisingly, muscle mass doesn’t contribute all that much to the total metabolic rate (skin and bone contribute even less), which gives the lie to that old notion — that I, myself, have fallen prey to — that replacing fat with muscle increases metabolism significantly.)
Therefore having a lot of muscle mass does not lead to a huge increase in basal metabolic rate. So if that's true, then why is it that some people eat more than others when they're the same size, and have the same level of activity? Why are some people big eaters and other people not?
Taking into account that it's the brain, heart, kidneys, liver, and GI tract that are using up most of the energy, we might ask: could a big eater have an inefficient liver? An inefficient heart? If your liver is damaged in some way could it be using more calories? If you spend all day thinking are you going to be burning more calories? (In my case I know it's not my big brain, ha ha.)
What if you have a long-term, low-level infection? Are you feeding a virus or a fungus? (Kind of like the tape-worm idea above ...) Or perhaps it's just miscalculation, overestimating how much you're eating -- the "big eater" is just a boaster and not a big eater at all? Or are some of us just built differently from others and that's that?
And here's another thought: If general appetite level is not changed by a switch to paleo does that give us any clues as to what the cause of that appetite level might be?