So if being fat is bad for people, than doctors should tell them not to be fat, right? Or at least tell them to eat vegetables and hit the elliptical, right?
Well, maybe. But sometime around age two humans realize that they are independent beings who do not physically have to do everything an authority tells them to do. Unfortunately, most doctors’ patients are over the age of two, and those that aren’t have their own issues.

Telling people to do things they already know they need to do has mixed results. Scott Alexander suggests alcoholism could be decreased by as much as 13% if doctors would spend five minutes telling alcoholics it was bad for them. What this doesn’t capture is how lectures change the doctor-patient relationship. It is very difficult to give a non-judgmental lecture when your billing model gives you 10 minutes per patient. Patients might avoid or delay visits for problems- alcohol related or not- in order to avoid the lecture. This is a pretty big issue with overweight patients, and apparently without upside: patients lectured by their doctors are more likely to attempt weight loss but no more likely to achieve it.
In this TED talk, Thomas Goetz talks about a study of dental patients (no cite, unfortunately) that found that scaring them had no effect, but patients’ belief in their own ability to floss had a large one. It’s impossible for me to separate my personal experience from this data. Multiple dentists and hygienists told me my pain was my fault for terrible oral hygiene, and if I brushed and flossed it would go away. This turned out to be untrue on a couple of levels. The pain was caused by structural damage and internal infection, which may have been made incrementally worse by oral plaques but wasn’t caused by it. And I was actually brushing pretty regularly, it just wasn’t do anything. Then I started treating a completely unrelated digestive problem, and suddenly my teeth were cleaner. I didn’t even tell my dentist anything had changed, she asked spontaneously. So I guess, yeah, patients belief in their own ability to effect change matters, and if they don’t believe it, maybe consider that they’re correct and investigate why.
But let’s go one step farther. Crum and Langer did an interesting experiment on two groups of hotel maids. Both were told exercise is good for you. One was given additional information about the intensity level of the work they did all day, and told just by going to work they were exceeding the surgeon general’s RDA of exercise. Four weeks later, the informed group was slightly thinner (they even checked body fat %. I am so pleased) and had lower blood pressure . Not astoundingly lower(10 points on diastolic BP), but it was only four weeks, and a pamphlet is even less work than a doctor lecture.
This suggests that one of the more helpful things public health officials can do is reinforce the good things people are already doing. You did a stretch? Hurray for you. Check parking lot twice before accepting a far out spot? Still counts. It would not shock me if part of the health improvements attributed to standing desks turned out to be simply a halo effect of feeling like you made a healthy choice. Which coincidentally is how you turn a two year old into a civilized human being.