I have recently been reading The Hacker' Diet (free and online), written some years ago by John Walker, a software millionaire who had succeeded, after many years of being overweight, in slimming down and getting fit. He took a very down to earth engineering approach, devoid of pseudo science, and full of lots of common sense.

One aspect he covers is the degree to which our weight varies from day to day. The diagram below is courtesy of NASA's Mars program, who had to think about such things. It shows the "Inputs" and "Outputs" of the human body, and the average quantity of each. What this shows so graphically is just how much "stuff" goes through the human body on a daily basis. It's also a great illustration of why you should not worry about your day-to-day weight, it can fluctuate by several pounds based on how much you drink, sweat, or err do the "other" things Most of your "output" is water!



What is important is the trend over time, so don't get too down at heart if you get up in the morning and have put on a couple of pounds, it's just your body doing its thing.

It also demonstrates one of the problems with the Wii Fit Fitness test, it measures and plots the absolute weight on the graph, and nags you if you put on weight. I think this is too harsh when done daily, and risks putting people off. Instead it, and you, should plot a graph of the "rolling average" of your weight. The simplest method is to just add up your weight over the previous five days and then divide by five. Plot both your actual weight and your rolling average on a chart each day, but only pay attention to the average line, it will smooth out those daily fluctuations, and give you a much better picture of your real weight.