Friday, October 25, 2013

scientific errors in medicine

The obesity-health saga is an interesting example of scientific error. There is a clear correlation between being overweight and having various health problems, particularly Type 2 diabetes. So nobody looked more closely at that. Everyone is advised to lose weight.

But then they did look more closely and low and behold we find: For most people, carrying extra weight is actually protective. At any given level of fitness it is better to have more weight.

So why is carrying weight associated with disease? The answer is that most people who are fit are relatively slim because it is hard to keep the weight on if you get fit. So being overweight is correlated with lack of fitness, and that is the problem. If you can be fit and keep the weight, with a high proportion of muscle, then that is ideal.

Medical science seems particularly prone to jump to conclusions based on correlation alone, but it is an easy mistake in many disciplines. Medical science is pretty good at other sorts of errors, including pure guesswork, like "eating fat makes you fat" (most people lose weight on a high fat low carb diet); or eating cholesterol will increase your cholesterol levels leading to heart disease.


  1. I'm not sure how the blogger-plus interaction works. A comment in + didn't turn up here. I looked in the settings and comments were effectively turned off?? Yet another trick to get us to use +? Well comments are on again. And I wonder if this will turn up in +, and/or my next comment there will turn up here.

  2. Even though posts are put on +, there doesn't seem to be any to-fro of comments. I'll put my comments on both.

  3. The thing that set me off on this line of thought was this article: The writer simply ignores the opposing point, which is that it is not important if fats are saturated or not. What is important is whether they are long or short chain. Coconut fat is saturated short-chain and there is good evidence of positive health value. However saturated fat tends to be long chain, and vice-versa for unsaturated. So it looks like another case where an incidental correlation with the real issue leads to the wrong conclusion. [However what really annoys me about that article is that it ignores the opposing point. I really hate the way debates about important facts, affecting public policy, are conducted in this way.]