1. Doctors don't need to wash their hands. Before the 1920's, it was not common practice for doctors to wash their hands with soap before working with a patient, or even between surgeries. Doctors didn't realize its importance until a Hungarian physician, Ignaz Semmelweis, discovered it was an effective means of preventing common diseases. Could you imagine a doctor performing a surgical procedure on you, right after he had his hands all up inside another patient? It used to happen.
2. Frontal Lobotomy for mental illness. In the mid 1900's, a procedure called the lobotomy was used in an attempt to cure mental illness. In fact, Antonio Egas Moniz received the Nobel Prize for Physiology or Medicine in 1949 for his discovery of the therapeutic value of the procedure in treating certain conditions. So what exactly is a frontal lobotomy? Doctors would impale a patient's head with a large needle, forming a rather large hole from the inside of the left eye socket all the way to the prefrontal cortex of the brain. Yes, they literally stabbed patients in the head. The procedure may have been somewhat effective in reducing symptoms of mental illness, but it predictably had side effects. As many as 3% of patients were killed by the procedure, according to the 1970 Psychiatric Dictionary. But besides that, it essentially made the patients easier to control by reducing their mental capacity. Good for nurses in the psychiatric ward, bad for humanity in general.
3. Exercise ruins your bones. This myth was commonplace until the 1950's. The typical conventional wisdom of the day was that resistance training wears down your muscles and bones, and should be avoided, especially by older adults who are at risk of degeneration and osteoporosis. Today, this sounds ridiculous. Personally, I don't know how anyone ever believed this. If you look at it from a historical perspective, always useful, people knew lifting heavy things was good for you as far back as Ancient Greece. Not sure how the message got lost in translation but, at least that myth is dead now.
4. The sun revolves around the earth. Yup. Before the early 1600's, everyone knew Earth was the center of the universe. That is, until Galileo Galilei came along with his telescope and determined mathematically that the earth was in fact orbiting the sun, not vise versa. The Roman Inquisition, of course, didn't like that because it challenged the Catholic Church's view that God created the earth and made humans to run the place because they are above the laws of nature because they can control it by growing their own food and invent new ones like bread, and by coercing formerly wild animals to live beside them only to be killed for their consumption. That may have been a run-on-sentence. But the point is we know now that the sun is the center of our solar system and Galileo was right all along. Take that Pope.
5. Cigarettes are endorsed by physicians. This one might not be too hard to believe, I mean considering all the drugs physicians support these days. But it's true, doctors used to support cigarettes for "throat protection against irritation against cough." Grammatical considerations aside, it actually took a long time for the tobacco companies to finally fall to the mound of data linking smoking to lung cancer. Today, it's widely accepted that cigarettes smoking does cause lung cancer, and we can all laugh about these old ads.
I'm sure there are plenty more examples of this type of thing, but my point with this post is to say that people today tend to think we know everything. These examples seem silly, knowing what we know today, but if you were able to take yourself back in time, you would probably accept the conventional wisdom just as everyone else did. So, next time you hear something that challenges your most precious beliefs about health and nutrition, or anything else for that matter, don't simply dismiss it because "everyone knows the truth." The conventional wisdom of the time is often far from the truth.