We talk on this blog a lot about how almost nobody succeeds at weight loss long term, and why that is. Today I want to talk about the rationale that we are given for pursuing weight loss in the first place. It’s a bit shaky when you realize that there is no study that shows that people who are able to maintain weight loss long term are healthier or stronger, and that almost every bit of “evidence” linking weight and health problems is correlational, not causational. Often the suggestion is that if enough studies show a correlation between size and health problems, we can safely assume that size causes the health problems and that changing someone size will cure health problems. Since weight and health are such charged subjects, let’s look at this through some other lenses.
The problem with correlational research is that it only shows that things happen at the same time, it does nothing to prove that one thing causes the other, and that’s where the trouble starts.
Many studies show a link between increased ice cream eating and increased murders. All I can definitively say from this is that ice cream eating and murders often happen at the same time. I cannot say that ice cream eating causes murders. I cannot say that murders cause ice cream consumption. If more murders take place I can’t say that there is an ice cream epidemic.
Since all I know is that there is a correlational link, I must acknowledge that it’s possible that the ice cream eating causes murders, that murders cause ice cream eating, that they are unrelated, or that they are both caused by a third factor.
Let’s say that the latter is true - that the cause of both issues is heat – when people get hot they tend to eat more ice cream, or become cranky and murder people.
But let’s say I don’t know that, and I assume that since there is so much evidence linking ice cream and murders, I can assume that eating ice cream causes murders. So I start a War on Ice Cream Eating! I lobby to get ice cream off the shelves, to get everyone to look at people who eat ice cream as horrible people who deserve to be shamed. I work tirelessly to get ice cream out of schools and away from our kids.
Not only is this misguided, if the truth is that when people are hot they either eat ice cream to cool off or they murder someone, by taking ice cream off the shelves I may actually increase the murder rate. And that’s why assuming cause from correlation is a bad idea.
Men who have male pattern baldness also have a higher risk of heart issues. The reason for that is that the same hormones responsible for male pattern baldness are responsible for increased risk of heart issues. But let’s say I assume that the baldness causes the heart issues. So I start a War on Baldness! I work with companies that claim they can grow hair and inform the public that bald men who aren’t using Rogaine or joining the Hair Club for Men are increasing all of our health care premiums. I create workplace incentive programs where men who are showing signs of balding are fined thousands of dollars unless they join “voluntary’ hair regrowth lunch meetings. I suggest that bald men may be unfit parents since it’s possible that they may be more likely to raise bald children. I pour millions into programs that give out toupees to bald men. By treating one of the results instead of the cause I can take attention away from treating the actual issue and increase heart issues in bald men, or delay treatment that is actually shown to help the heart issues because I’m busy trying to treat the wrong thing. And that’s why assuming cause from correlation is a bad idea.
Large bodies have been correlated with some health problems. Let’s say that I assume that body size causes those health problems. So I start a war on obesity. I direct all public health efforts toward trying to figure out how to make people thin, I direct public health messaging to be about how fat people need to become thin to be health. Doctors start to tell fat people that becoming thin is the way to prevent these diseases, even though thin people get them too. By doing so I direct attention and treatment away from actual healthcare interventions and toward body size interventions, rolling the dice that changing body size will lead to health and blaming fat people if it doesn’t work. And that’s why assuming cause from correlation is a bad idea.
For more fun with correlation, check out this article!
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