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Wounded knee, calories and causes

A few weeks ago I tripped and fell, twisting my knee. It was a very contemporary trip, I was consulting Google(tm) maps on my iPhone(tm) at the time.

As joint injuries do, it is taking a long time to heal. A couple of weeks later, I was stretching my leg as straight as I could get it when it was nice and warm under the blankets, there was a distinct "click" and my knee has been (slowly and erratically) getting distinctly better since.

But, judging how it feels when I first get up in the morning, exercise the day before (particularly doing Heavy Hands(tm) or long walks) seems to be good for my wounded knee, even if complains at the time. Sitting on a stool is good, on a kneeling chair not so much.

Still, it does provide another reason to keep up with my exercises.

I have also been reading Good calories, bad calories. The point that the author makes that the second law of thermodynamics is an equation, not a causal statement, is a good and powerful one. (Or, more precisely, there is causation underlying it but the equals sign does not tell you where it is.) This refers to the weight = calories + exercise notion of weight loss. His point being that if what you eat affects your propensity for activity, then the causal relationship is not anywhere as simple as it is often portrayed. Particularly given the tendency for people to achieve stable weights. Your body's overall weight equilibrium is the result of a whole lot of cellular equilibriums: so if certain foods encourage energy and so activity while other foods encourage searching for further nutrition then your weight is not going to be a matter of mere calorie counting.

The burden of the book is that fat has been much maligned (Americans have been getting fatter while their intake of fat has been declining), but the news on sugar and simple carbohydrates is basically all bad (for both health and obesity). I was struck particularly by the story he tells of certain individuals with academic authority going on public crusades based on very limited or ambiguous evidence. Once something becomes "conventional wisdom" -- particularly if it becomes tied to government funding and media presumptions -- it can be very hard for counter evidence, no matter how powerful, to make headway. People have their "accepted and authoritative" frame of (cognitive) reference and they just go with it, with each iteration adding to its power as "accepted and authoritative".

Taking the book's broad advice, I have found that cutting back on the sugar and (particularly) simple carbs does seem lead to more energy and less weight. I am also cooking with butter (which tastes better anyway, and you do not use very much) and using the creamy yoghurt (which tastes better, has less sugar and not much more fat).

Heat oven to about 240oC. Grease baking dish with butter. Slice sweet potato relatively thinly. Place dollop of pesto on each slice. Bake for at least 20 minutes at at least 200oC. Remove and serve. (Yes, the pesto will go black, that's fine.)

Aggregate error
I was particularly struck by the author's point about the second law of thermodynamics, as you get the same error being made in economics with causal misreadings of (aggregation) equations. Take the "Keynesian" equation of
GDP = C + G + I + X - M
(Gross Domestic Product = Private Consumption + Government Consumption + Investment + Exports - Imports).
This measures the results of actions by a mass of agents (like the cells in a body). It leads to Twin Deficit analysis where
(SP - Ip) + (M - X) = (Gp + TR - T)
(Private Saving - Private Investment) + (Imports - Exports) = (Government purchase of goods and services + Transfers - Taxes).
Or, to but it even more simply:
Net Saving + Trade Balance = Budget Balance
The basic idea behind the Twin Deficits hypothesis is that there will be a connection between the government budget surplus (T > Gp + TR) or deficit (T < Gp + TR) and the trade surplus (M < X) or deficit (M > X).

There are two problems with this. First, even in the equation there is the issue of (SP - Ip): if the actions of the government affect either private investment or saving, then there will be no simple connection between the budget balance and the trade balance. Changes in the budget balance could literally have any affect on the trade balance, depending on the response of private agents to both the way the deficit or surplus was generated and to the overall budget balance.

The terms in the equations are aggregations of billions of transactions by millions of agents. The agents drive what happens, not the aggregates. (Yet another iteration of the basic point of economics: incentives matter.)

Second, and extending the first point further, there is no causality implied in that equals sign. So, returning to the second law of thermodynamics as applied to nutrition, one could equally say weight - calories = exercise. Or weight - exercise = calories. There really is no causality implied in an equals sign (even when there is causation underlying an equation) when one is dealing with aggregates based on actions of a mass of smaller functioning things -- whether it is body cells or economic agents.

So, the next time people say or imply that weight is "just" a matter of calories and exercise, remember that an equals sign involving aggregates does not imply causality and your cells are massively more complex than that: just as how a government generates a budget balance matters, so how you get your calories matters. As your feelings of lethargy, energy, sleepiness, satiation and hunger will remind you.

ADDENDA: This post has been amended to make it clear that I am talking about equations involving aggregates.


( 3 comments — Leave a comment )
Apr. 25th, 2011 09:11 am (UTC)
That fact that you can move elements of an equation around doesn't remove the fact that the equation (not the equals sign in it) implies causation. You can do the same thing with F/M=A (force divided by mass equals acceleration) but that doesn't change the fact that if you apply as force to a mass then the force will most definitely be the thing that causes the acceleration. So while there are surely going to be metabolic issues that affect the ways in which you metabolise food and how efficiently and whether you'll be better able/more motivated to exercise, I'd still suggest that energy has to come from somewhere and if you don't make use of it then it's still going to be stored unless you can induce the body to just pass it straight through (and that particular strategy has own special issues). So I'm not seeing the ability shuffle variables in an equation as invalidating the scenario that equation represents, whether it says "basal metabolic load + exercise - calorific intake = net body mass loss or net body mass loss - calorific intake + basal metabolic load = exercise. One shows the result of a given food intake and amount of exercise, the other allows you to derive the exercise level required to produce an equation that's balanced for the other given values.
Apr. 25th, 2011 10:36 am (UTC)
Your first point is a good one and I have changed the post to reflect the fact that it is about equations involving aggregates. It is treating the aggregates as single things which causes the problem.

Your second point, since it expands to cover aggregates, does not work so well. The point the book makes is the form by calories are ingested of itself affects one's propensity to engage in activity, to store fat or to pass it through. The equation has causation underlying it, but the equals sign does not tell you where that is.
Apr. 25th, 2011 02:57 pm (UTC)
If cal_in - cal_out is bigger than zero, then you gain weight. If it's less than zero, you lose weight. This agree with.

What's misleading about it is that cal_out is a function of cal_in. You change cal_in, that's going to change cal_out. In some people, increasing cal_in increases cal_out (they start fidgeting more). I can't recall a simply study saying that reducing cal_in reduces cal_out, but it certainly seems likely.

It takes very small changes in number of calories consumed to result in changes in weight. A fifty calorie a day difference--that's about 2% of the day's intake--results in a 5lb change over a year. Yet people don't swing in weight very much if left to their own devices. Somehow, there's some internal regulatory system that adjusts appetite and activity to ensure that weight stays pretty steady. If you're trying to lose or gain weight, you're fighting that very effective internal regulatory system.
( 3 comments — Leave a comment )



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