Kevin Drum asks

Now, there are a bunch of things you might say about this right from the start. Maybe governments shouldn’t be in the business of running nanny state ads about personal nutrition. Maybe this particular ad was disgusting and shouldn’t have been released. Maybe obesity isn’t really that big a deal in the first place. But those weren’t the issues at stake. Rather, it was this single sentence in the ad:

Drinking 1 can of soda a day can make you 10 pounds fatter a year.

What, I thought, could be wrong with that? A can of sugared soda contains about 150 calories, and adding 150 calories a day to your diet would almost certainly produce a ten-pound weight gain over the course of a year or so. There are some caveats, of course:

So I’m curious: what do you all think of this? I’m open to argument here, but it seems crazy to me, less a politicization of science from the health commissioner than a case of geekdom run amok among the scientists. I mean, if you can’t tell people that adding a bunch of calories to your diet will make you gain weight, what can you tell them?

The problem is that the calorie balance interpertation implies a completely false understanding of what is going on. There is an extent to which geekdom can tolerate this level of nonsense and there is a point at which it must be combated.

I will compare to something I know Kevin gets. The calorie balance logic is equivalent to saying.

Government deficits drain savings. Savings are the engine of growth. Therefore, cutting the deficit immediately is our best shot at growth.

In both cases you are taking an accounting identity

  1. Private Savings – Public Borrowing = Net National Investment
  2. Calories-In – Calories-Out = Calories Contained in the Body

And, treating it as if it were a model of the world.

You have to be aware that public borrowing might effect private savings. In particular if public borrowing stimulates the economy it will increase private income which in turn will increase private savings.

You also need to be aware that Calories-In affects energy and hunger levels which not only feeds back to Calories-Out but also to other Calories-In.

I used to post this thing a lot, but since the blog has new readers it might be worth our while to look at how a properly functioning metabolism responds to a rapid increase in Calories-In

The big question we have is why does this stop working in some people? Just to note, there are many, many other feedback loops that are important as well. I point out this one because it so obvious both that it works in the healthy metabolism and that it fails in the unhealthy one.

You are probably aware of the relationship between diabetes and obesity. It is commonly assumed that obesity causes diabetes. This is in part because even some scientists are fixated on the accounting identity. However, there is a reasonable case that diabetes may cause obesity.

That is, the resistance of the muscles to insulin causes the breakdown in the “sugar rush” response (and other loops) which then breaks down the feedback from calories-in to calories-out.

Now, if it is in fact the case that sugary drinks induce insulin resistance this connection may still hold. However, it is almost certain that the simple minded thinking that in general dropping a 150 calorie item from your diet will not feedback on other metabolic components promotes a fundamental misunderstanding of what’s going on.

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For the geeks. Yes, in truth even what I have written here is a gross oversimplification and ignores central facts such that an increase in obesity from sugar consumption must be proximately caused by an increase lipogenesis or a decrease in lypolysis both of which are hormonly regulated processess. That is, just as there is no such thing as immaculate transfer there is no such thing as immaculate obesity.

You can’t just throw organic matter at a metabolism and get fat. You actually have to create fatty acids and bind them up into triglycerides. Any model that assumes that you can is going to wind up disappointing you and of course there are a fair bit of disappointed dieters. We need to do better as intellectuals.

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