For me, an important part of preparations for the Malvern Midsummer Marathon in June 2013 is shedding of excess mass. Specifically, the excess mass accumulated through a job that involves a lot of sitting at a desk, sitting behind a steering wheel or sitting at a meeting room table, plus innumerable buffet lunches… This kind of lifestyle takes its toll eventually.
The target was to lose at least 3 stones, that is about 19 kg. I’ve achieved most of this through simply eating less, and in particular cutting out afternoon chocolate bars and evening biscuits. It has taken about 16 months to achieve the target at a steady pace as the graph shows.
Losing weight did become more difficult towards the end and at this point it seemed like a good idea to get a bit more exercise and also add up my daily calorie intake for a few months to make sure that I was staying on course. Counting the calories and plotting against weight loss has allowed me to generate interesting graphs that lets me see exactly how many calories I can get away with eating with my current lifestyle without putting on any weight.
Now, the “received wisdom” from healthy types is to not to weigh yourself daily as the daily variability in your weight depends greatly on what you have eaten, how hydrated you are etc., and therefore looking at daily weight changes is pointless. As a scientist, the idea of collecting less data rather than more is of course complete nonsense – what you do is collect as much data as you can and then process it accordingly. The graphs below display show average daily weight loss plotted against average daily calorie intake minus an estimate of calories burned through exercise (e.g. running) for a series of averaging periods: 1 day, 7, 14, 21 and 28 days. There are two sets of data on each, one the raw data and one (the trend) that has had some day-to-day smoothing applied (using the Libra Android app).
What you can in fact see is that looking for daily differences in weight in the raw data does give you a rather scattered graph, but in fact the daily trend data is considerably less scattered. So with appropriate processing daily weight measurements can give you a good idea of progress. The subsequent graphs averaged over longer time periods show that the random errors gradually cancel out. There is a trend of the gradient of the trend line going down (smaller weight loss per kcal) but an increase in the zero weight change intercept (more calories can be consumed for no weight change). I’m not quite sure what to make of the trend of the gradients and intercepts, but the general picture is that to maintain a constant weight in a lifestyle with limited exercise I need between 2150 and 2250 kcal per day. Exercising means I can eat more pies, chocolate and biscuits without putting on weight.