I browsed through a book yesterday called "Don't Swallow Your Gum! - Myths, Half-Truths, and Outright Lies About Your Body and Health". It debunks a number of common misconceptions that many people hold to be true.
One is that we only use 10 percent of our brain. If this were true, it would not be a big deal to hurt various parts of your brain. In reality, you will be affected by damaging almost any region of your noggin.
Another is that you should shit (or poop, for the more sensitive among us) at least once a day. Constipation is actually defined as having less than three movements in a week. This reminds of something amusing I witnessed at a psych ward a number of years ago. I was visiting a patient there on a regular basis and each evening, the patient would be asked if they'd had a bowel movement that day. Some of the nurses would just go up the person and say, "Did you....?" Talk about embarassing, for both parties, I gather.
Course, we all know that cold weather doesn't make one sick. Vitamin C was also debunked at being able to keep a cold at bay. Another classic is that men think about sex every seven seconds which is patently ridiculous. This would translate to thinking about sex over 57,000 times a day. That's about as many times as a person breathes while awake. Someone thinking about sex that much would be incapable of performing any other tasks.
There is also a persistent belief that eating at night makes you fat because it doesn't give you any time to burn off those calories before going to bed.
I know this isn't a truism as I eat the bulk of my calories after 9pm. I have several food items, in fact, every night just before going to bed; typically a Smart Ones pizza, a couple Oreo Cakesters, some chips, and a Nutri Grain bar.