Bro Science is science that isn't really science, but a Bro (i.e., big jock with muscles, someone famous, or just someone you trust) says something with great sincerity and belief. Heck, I've probably done my share of BroSciencing and my degrees give me credibility, whether I deserve it or not.
A couple more thoughts. Some BroScience is really marketing science. Some people hype scientific sounding stuff to sell their stuff. That's actually easier to deal with than the people who are true believers in something that is just wrong. They don't send any of the usual warning signals that trigger our BS detectors.
Here's some things I think may be BroScience.
Free weights are better than machines.
You can't lose fat and gain muscle at the same time.
Low carb diets cause your thyroid to crap out.
Carnivorous humans have up to 40 pounds of rotting meat in their colons.
Just about anything else about "colon health."
Vegetarian diets are healthier than omnivorous diets.
Dietary saturated fat is bad for you and will cause heart disease.
It is good for you to keep LDL levels below 100, and below 70 if you have heart disease. (these are based on something called "expert opinion", not on randomized trials.)
Something I keep reading about but just haven't seen any real science on (doesn't mean it doesn't exist, just that I haven't found or seen it yet.)
The whole deal about omega 6 unsaturated fatty acids being "inflammatory." Now I know that they get turned into inflammatory compounds in the body, BUT it's not necessarily true that eating more omega 6's automatically raises the levels of the inflammatory compounds. The body MIGHT just burn up the excess. Again I just haven't seen it.
Actually "inflammatory" in general seems like a BroScience buzzword.
Years ago on a radio call-in show someone called with the claim that at autopsy John Wayne (must have been Paleo as manly as he was, right?) had 40 pounds of rotting meat in his colon. A brief internet search revealed that the claim must have been bogus as he was not autopsied! Also I can tell you after doing hundreds of autopsies myself that I've never seen this 40 pounds thing happen. BroScience or Urban Legend, take your pick. It is BS!
By the way, there are some words that tickle MY BS detector after doing that show for several years.
1. "Toxins." People blame "toxins" for all kinds of things. Toxins are real, but I think get blamed for a lot of lifestyle defects.
2. "Parasites." Listen. I have a PhD in Microbiology and I find parasites particularly fascinating. I've diagnosed a lot of them in my life. They are rare in the US. Rare. They sound icky and make great marketing material; who wants to be harboring a parasite? Unless you've been to the third world and been careless I can pretty much guarantee you don't have one!
3. "Colon health." Goes along with all kinds of awful treatments: enemas, purgatives, fiber supplements, etc. I don't know why the colon holds such fascination for people. I remember my mother telling me (we were watching TV) that "regularity" which seemed to be the goal of any healthy person simply meant having a bowel movement daily. Important? Not really.