19 May 2020

Spurious Accuracy

I haven't mentioned it a lot, but I have been actively trying to lose weight for the last twenty-six months or so, after hitting a peak BMI in excess of 40 (which is "severely obese" a.k.a. "morbidly obese" a.k.a. Class III obesity), and being diagnosed with Type II Diabetes in April of 2018.

I've made great progress since then. I lost about 60 pounds, gained about 25 pound back, and using Noom.com since the lockdown, I am back to being down about 65 pounds from my peak weight. I am no longer diabetic (and probably not even pre-diabetic), and my other blood and urine test chemical markers for cholesterol, triglycerides, and other stuff that you get too much of when your overweight and don't exercise are back to the good range. 

Mostly this has been a result of dieting, and exercise options have been greatly limited during the lockdown, but I'm walking more than I have since I was a precinct committee person, walking blocks in the neighborhood several times a year to distributed political fliers, something that a back injury prevented at that level for many years.

I've lost more than 20% of my body weight, and I am currently on track to bring that to 25% and to reach a weight at which I am merely "overweight" rather than obese by sometime in July when I conclude the weight loss program I started on March 21, 2020. I am less than 5 pounds away from weighing less than I have at any time that my college aged children have been alive (that was for a month in the summer of 2009, from much higher weights before and after that episode of weight loss, probably associated with a South Beach diet effort).

Anyway, back to the point of this post.

When you are on a weight loss program, one of the things you do is weigh in regularly. I do it every morning right after I wake up and have gone to the bathroom, before breakfast, and record it in an app.

My bathroom scale provides a weight with a 0.1 pound precision. It probably isn't actually that accurate, but it's close. 

But, when it comes to measuring weight, a bathroom scale has spurious accuracy. The frustrating reality is that a person's body weight at any one time, even if calories in equals calories out exactly, every single day, isn't that stable or constant. Not even within an order of magnitude of that.

Your body weight varies during the course of the day, and from day to day, in a manner that is more or less random. When you last pooped, peed, ate, or drank something matter, as well as other factors I can't really explain at all. 

Since I'm a big guy, even with my weight loss progress to date, the raw numbers are pretty significant. I haven't actually crunched the numbers (yet), but I'm numerate enough and work with data sets, probability, and statistics enough (mostly in my hobbies), that I have a pretty good feel for what a margin of error in a data set looks like. In my case, one standard deviation of random noise in my day to day, and hour to hour, weight is about 1.5 pounds. This means that over the course of a couple of months, I'll see about three days with a random noise weight change of more than 3 pounds, while I much more frequently will see a day to day random noise weight change of one or two pounds.

You have to look at a longer term charge and smooth out the day to day noise to see the long term shift in the midpoint of your regular daily noise fluctuations in weight. 

It takes about 3500 dieter's calories (kilocalories) of eating less and/or exercising more than you need to in order to maintain your existing weight to lose a pound. A pretty strict diet and exercise regime aimed at rapid weight loss has you eat about 500 to 700 calories a day less you burn through daily activities and exercise combined, which means you should lose an average of 1 to 1.3 pounds a week (I personally have been losing a bit more than 3 pounds a week during the lockdown so far, although I'm well aware that plateaus can and will interrupt that progress.)

So, psychologically, this means that weighing in sees you routinely move as much as three weeks backward or forwards on your planned long term weight loss pace in a single day. This makes it much harder to cling to the (well founded) faith that you have in your plan that if you stick to it that the long term results will arrive in due course, despite the confusing day to day random weight noise.


Dave Barnes said...

I will drink a beer today to help you along your path.

andrew said...