Short version: I was thinking about how long things last. I’m looking for a good methodology for self-experimentation.
This week I was thinking about flow, particularly through a reservoir or storage vessel, as a model for people and cities. The intuition starts with a bucket, being filled by a dripping tap and emptying from a small hole in a bottom, such that the amount of water in the bucket is fixed. Over some amount of time, all the water that was in the bucket will be replaced. If the flow in and out is very small relative to the size of the bucket, the time to replace every molecule of water in the bucket is very large (as the molecules become less concentrated, more new molecules are lost in each drop out), where the extreme case has the no flow and the original water stays in the bucket forever. In other extreme, where the hole and tap are the so large that the entire volume of the bucket is replaced with each drop, it is essentially a pipe and so the replacement rate is essentially infinite (though there is a speed with which molecules diffuse against the direction of flow in a pipe, perhaps something to look into later).
I will update this post shortly with some more thoughts, but taking as an example the question “how much of the bone in your body is made up of calcium consumed by your mother”:
1000-1300 mg/day (calcium intake) = 32.5 mmoL per day in/out. We assume some constant calcium mass in the human body e.g. 1.5% by mass calcium so for 75 kg= 975 g calcium. Probabilities give p(excretion in a day) = 1.3/975 so p(remain) = 1-(1.3/975) = 0.9986 per day = 61% remains per year = 0.61^(age in years) = amount remaining, so after 100 years 7.08e-22% remains or 10 molecules from birth. This of course is very crude. People are not born with the same weight of bone as an adult, which would make this an overestimate of calcium remaining. However not all the body’s calcium is replaced equally frequently, some may be trapped much longer deep in thick pieces of bone, meaning the flow estimate would underestimate. Suffice to say, I confidently predict we all have some calcium in our bodies originally consumed by our mothers.
Supplements and Superfoods
I’ve been hearing bits and pieces about “superfoods”, dietary supplements, and generally nutrition comes up when eating with others. There’s a lot to be skeptical about when it comes to alleged benefits of oils, powders, and pills, as the authors of Reality check: no such thing as a miracle food discuss. I’d be interested in testing the effects of some of these, being inspired by the likes of Tim Ferriss or Peter Attia, but I don’t have an obvious experiment in my head. If you have suggestions I’d love to hear from you, and will try and look more into the literature around nutrition. A good starting point on supplements is this NHS report.