Reddit reviews Gulp: Adventures on the Alimentary Canal

• Naked Statistics by Charles Wheelan is a great overview of the science of statistics, without being too much like a lecture. After reading it, you'll have a better understanding of what statistics are just silly (like in ads or clickbait news) and what are actually important (like in scientific studies).
  
  
• You on a Diet by Roizen and Oz is touted as a diet book, and it kind of is. I recommend it because it's a great resource for basic understanding the science behind the gastrointestinal system, and how it links to the brain.
  
  
• All of Mary Roach's books are excellent overviews of science currently being done, I've read Stiff (the science of human bodies, post-mortem), Spook ("science tackles the afterlife"), Packing for Mars (the science of humans in space), and Bonk (sex), and they are all very easy to understand, but scientifically appropriate. I'm sure "Gulp" is good too, although I haven't read that one yet.
  
  
• "How I Killed Pluto and Why It Had It Coming" by Mike Brown is a great, accessible overview of exactly why Pluto was demoted to dwarf planet, told by the man who started the controversy.
  
  
• "A Brief History of Time" by Stephen Hawking is a little denser, material-wise, but still easy to understand (as far as theoretical physics goes, at least!). Hawking explains the history of physics and the universe, as well as the future of the discipline. While there is a bit more jargon than some pop-science books, I think an entry-level scientist can still read and understand this book.
  

Three books if you're interested in this subject:

Gulp: Adventures on the Alimentary Canal

Missing Microbes by Blaser

Life On Man, by Rosebury.

Blaser is one of the leading researchers in the field; Rosebury was a noted microbiologist who- at one point- headed up a bacterial warfare research program at Fort Detrick (now USAMRIID).

The short answer to your question: the environment. The longer answer is that it is a function of exposure from mom (including birth- the bacterial flora in the vagina changes in the third trimester- which raises some interesting questions about the effects of C-section), the family (which would make for some interesting studies in adopted children), the environment (lactic acid bacteria, etc.), and is modulated by things like diet, and antibiotic use.

Interesting note by Blaser: Helicobacter pylori, which has been implicated in ulcers, may be protective against asthma and allergies.

Now- this is the gastric environment, versus the intestines- and not many bacteria survive the stomach, so H. pylori is a minor but important subset of bacteria in the digestive tract; by numbers, it pales in comparison to those of your colon, for example. But it is rapidly being depleted in Western populations from antibiotic use- including abx that are not prescribed for such use. So, we're losing these bacteria that we can demonstrate have been colonizing our stomachs for tens of thousands of years, and the big question is whether this could be where we're getting the increase in asthma and allergies from.

Very hot topic just right now, lots of interesting work being done.

Right now I'm reading Gulp: Adventures on the Alimentary Canal by Mary Roach. This passage might actually help:

>Defecation, orgasm, and arousal all fall under the purview of the sacral nerves. The massive vaginal stretch of childbirth sometimes produces orgasm as can, at least in one diverting case study, defecation.

Okay, super gross, I know (the whole book is gross but fascinating), but the point is that there are a bunch of shared nerves down there. I'm no scientist, but if those crossed wires can sometimes result in orgasms via pooping (or anal stretching, something else she mentions in that chapter), maybe they can also result in sympathetic contractions when you're having cramps.

Also, I'm pretty sure I've experienced the same thing! Especially since getting my IUD, which has made my cramps much nastier.

Tell your friends to read Mary Roach's book Gulp. She has a whole chapter on enemas (as people used to think you could get nutrients/vitamins that way) and things just simply aren't taken in like that — as far as the hydration goes.

Her most recent book, Gulp, which came out just a couple of months ago, does for your understanding of your digestive system, what Stiff does for you when you see dead people.

http://www.amazon.com/gp/aw/d/0393081575
Or
http://www.amazon.com/gp/aw/d/0393324826/ref=pd_aw_sims_3?pi=SL500_SY115

I recommend reading Gulp for your horror and amusement.