Interesting. So you're saying that it's a poor approximation because 1) He just counts incoming calories, but there is a difference between sugar calories and olive oil calories (for example) and 2) He ignores the output of the system As far as I can tell, the basic process is this: Count incoming calories daily Take weight daily Note extra exercise or activity After a suitable history of calories, weight, and exercise is logged the algorithm then indicates how many calories you should be eating daily to maintain a stable weight. This appears to be a fairly closed system. Your points are valid - he doesn't differentiate based on the type of food, nor does he accurately track the output of the system. Knowing the input and the weight change, one can only approximate the output. However, it appears to be self adjusting - if you spend three weeks eating nothing but sweets, the daily calorie value will change accordingly. So I fail to see how it's not systems engineering. If I'm working on a system and I can only conveniently measure a few inputs and a few outputs, then I still consider it systems engineering even if I don't have a complete set of data. It's a rather loose loop, but it is a closed loop system. I suppose the issue, however, is what is considered an essential element of the system. A more rigorous examination of the problem would show just how much better the system could be controlled when the output and input are more accurately measured. I suspect that a large increase in accurate data would only yield a small performance/efficiency increase. -Adam On 12/20/05, Gerhard Fiedler wrote: > M. Adam Davis wrote: > > >> Seriously, from a systems engineering standpoint that approach fails > >> quite a bit. > > > I what ways does it fail? Like any approximation it can't take > > everything into account, but from a general overview what goes in must > > come out as either energy or matter. > > Right. But he equals energy (kcal) with matter (weight). That's probably > quite a bit short of the physiological reality, and exactly the difference > between energy and substance (that is, that the metabolism does see a > difference between e.g. sugar and olive oil) is the basis of many other > dieting approaches that he so quickly discards. Then he completely ignores > what goes out; there is the first picture with something going in, > something going out, and something being consumed, but after that, he never > talks about it again and just ignores what goes out, apparently assuming > that it is either constant or doesn't matter. > > Two major issues, IMO. Every model is an approximation, I know that, but I > also know that from a systems engineering standpoint you can't expect too > much from a model that doesn't cover essential elements of the system. > > Gerhard > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist