
Closed-loop body weight control - kasperni
http://blog.ifac-control.org/2016/12/05/closed-loop-weight-control-the-power-of-feedback/
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JPLeRouzic
I find this interesting as for long decades I gained weight (~1kg/year),
topping at a BMI of 34.

Then I had some health problems and decided to weight myself everyday in
exactly the same conditions, which is not easy to achieve over a long period
of time. At the same time I refused any of the small social transactions like
shared cookies, etc. I also wrote my daily weight in an Excel file.

Since 1.5 years I lost 1.5kg each month, then weight stabilized at a BMI of 31
(still obese).

Loosing so much weight (25kg) is frightening, is it a cancer? My wife and
myself joked about the power of the Excel file. When I read this article I
made a correlation between the proposed approach and mine.

However in the article the duration was only one month, often people gain more
weight afterward than they lost (I learnt it the hard way several times), and
in only one month the social cost is bearable, try to do that for years, your
friends and family will slowly learn to hate you, even if doing that means
your health is improving.

(edited for typos and clarity)

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kranner
> decided to weight myself everyday in exactly the same conditions

Water weight fluctuates too much day-to-day anyway. It's probably better to
consider a moving average of the last n readings than to bother to control for
conditions.

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JPLeRouzic
Yes, that what people usually says, but the article says exactly the contrary.

Anyway I don't see why it makes more sense to make readings everyday and make
an average on the last n, then use this average to make a continuous set of
decisions. What you are probably thinking, is about making _one_ decision,
like "do I have to diet or not?". It is also the case if someone is only
slightly interested in her/his weight, for me I weight in exactly the same
conditions everyday. I told it in the previous post, it's a bit hugly on the
social side, it has to be an obsession to make it work.

My main question everyday is: How my weight relate to last day meals, and
there is a very close correlation, that why it is so useful to weight often.

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akjainaj
Can somebody explain this to me like you'd explain it to your grandmother?

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jamessb
We want to control our body weight (system output) by altering how much we eat
(system input), based on measurements of our weight, so that it follows a
particular trajectory. We could simply try to calculate how much we should eat
ahead of time based on this trajectory and our initial weight, and then follow
this schedule without updating it based on any subsequent measurements ("open
loop control"). However, this would require a very good mathematical model
that can accurately predict future weight based on current weight and food
intake. If we instead choose how much to eat based on continuous measurements
of our weight (using feedback to achieve "closed loop control"), we can get
away with using a much worse model; this is one of the key advantages of
feedback.

The proposed control algorithm is simple: when eating a meal, eat a total
weight of food and drink (F(t)) that is the weight you would like to be at the
end of the meal (r(t+T)), minus your weight at the start of the meal (w(t)).
This rule ignores metabolism, so you will fall below your target weight by the
next meal, but you will eat accordingly more then.

Obviously, as the article notes, this requires that "the reference r(⋅) has to
be chosen larger than w(⋅) at all times". You can see this in Figure 1: the
measured mass starts below the reference, then increases up to the reference,
then falls below it, then increases up to it at the end of each meal.

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popra
You are awesome for taking the time to explain. Thanks.

