Some of us are tall, some of us are short. Some of us can run fast, some can’t. Some of us can do complicated math in our heads, others can barely do addition on paper. Some can sing beautifully, others sing like me.
It goes without saying that attributes we can’t directly observe must vary from one person to another as well; the only question is, by how much? And how can we tell? There is a tendency to believe that what we can’t or don’t measure doesn’t really have much effect. But that’s often far from the truth.
In particular, I am curious about the variance in our digestive system’s capacity to metabolize the calories we throw its way. If a thousand people eat essentially identical 300-calorie PB&Js, do we know anything about how different people in that group will turn the PB&J into different quantities of ATP?
The first place I’d look is Biochemical Individuality by Roger Williams. If I hadn’t lost my copy somewhere along the way, I’d check it myself, but since I did, I can’t. It was written in the 50s, so it won’t have current (or even recent) research, but you’d be amazed at what was known back then and hasn’t trickled at all into the popular press.