Our Absurd Fear of Fat

[eridani]

Our Absurd Fear of Fat
Paul Campos

http://www.nytimes.com/2013/01/03/opinion/our-imaginary-weight-problem.html

To put some flesh on these statistical bones, the study found a 6 percent decrease in mortality risk among people classified as overweight and a 5 percent decrease in people classified as Grade 1 obese, the lowest level (most of the obese fall in this category). This means that average-height women — 5 feet 4 inches — who weigh between 108 and 145 pounds have a higher mortality risk than average-height women who weigh between 146 and 203 pounds. For average-height men — 5 feet 10 inches — those who weigh between 129 and 174 pounds have a higher mortality risk than those who weigh between 175 and 243 pounds.

Now, if we were to employ the logic of our public health authorities, who treat any correlation between weight and increased mortality risk as a good reason to encourage people to try to modify their weight, we ought to be telling the 75 million American adults currently occupying the government’s “healthy weight” category to put on some pounds, so they can move into the lower risk, higher-weight categories.

In reality, of course, it would be nonsensical to tell so-called normal-weight people to try to become heavier to lower their mortality risk. Such advice would ignore the fact that tiny variations in relative risk in observational studies provide no scientific basis for concluding either that those variations are causally related to the variable in question or that this risk would change if the variable were altered.

This is because observational studies merely record statistical correlations: we don’t know to what extent, if any, the slight decrease in mortality risk observed among people defined as overweight or moderately obese is caused by higher weight or by other factors. Similarly, we don’t know whether the small increase in mortality risk observed among very obese people is caused by their weight or by any number of other factors, including lower socioeconomic status, dieting and the weight cycling that accompanies it, social discrimination and stigma, or stress