I've had a weak stomach since I was little, but recently it got worse and in new ways. A few doctor's visits later I have something to blame: celiac disease, where gluten in my diet causes an immune reaction and damage in my intestines.
Gluten is a fashionable topic, especially in San Francisco. You'll meet people here who avoid gluten "just in case" (here's NYTimes on that); my brother's reaction to my news was to call me a "glutard". But while there is a spectrum of reactions to gluten that are hard to quantify, I learned that in the case of celiac disease the diagnosis is pretty specific: first a blood test then a biopsy of the stomach and intestine.
There's also genetic factor in the disease. Looking back now over the various dooms that 23andme predicted for me, it spotted that I had the gene and put me at 2.54x the average risk for celiac — though that only implies a 0.30% rate. Here's an interesting note from Wikipedia about the genetics:
Given the characteristics of the disease and its apparent strong heritability, it would normally be expected that the genotypes would undergo negative selection [... compare to how quickly lactose intolerace disappeared... however,] there is evidence of positive selection in CD genotypes. It is suspected that some of them may have been beneficial by providing protection against bacterial infections.
Beyond that, the cause is still kind of a mystery. Here's my selection for the best article discussing the mystery of its prevalance with some history. That one also describes the interesting study comparing neighboring people on the Finland/Russia border with similar genetics/cuisines and a significant difference in incidence, which suggests it has something to do with the balance of intestinal bacteria.
Now that I have a diagnosis it's mostly just kind of inconvenient. My diet didn't center around wheat before so it hasn't changed dramatically. Eating at restaurants can be annoying, but the world is much more adapted to celiacs today than it was before (I was surprised to read Italy described as "heaven" for celiacs). What I miss most is beer. At my work they serve dessert at lunch and I used to eat two or three desserts a day along with cookies later, all of which are now off-limits. (Somehow despite dropping both beer and dessert from my diet, months later I weigh exactly the same — a little bit on the skinny side of normal. Diet is a real mystery.)
I think of my friends with much worse afflictions like Crohn's and in a weird way I feel lucky: that the diagnosis was quick (the internet is filled with stories of people who were miserable and undiagnosed for years), that it is not something more serious, and that my relatively mild symptoms have an explanation and treatment.
Getting sick has given me a new sympathy for others who are sick. I understood in principle how feeling bad all the time affects your mood, but theory is no substitute for experience. No matter how hard you try being in pain makes you grouchy and affects all your relationships. In particular I hadn't appreciated how much unpredictability affects your life. It's difficult to make plans with friends when you aren't sure how you're going to be feeling, and when you're feeling extra bad it's frustrating and scary to not know why or whether if you'll be fine in a few minutes or hours.
These days, months after my diagnosis, I feel much better but still not 100%. I find I keep accidentally dosing myself, like the delicious Arabic food last week where I didn't notice the noodles in the rice, and I hope that is the cause and not some as-of-yet undiscovered problem. Sources also disagree about whether soy sauce or whiskey is ok (I've been avoiding both). I am eager to feel well enough to establish a reference point so I can experiment a bit; I've already mentally designed some double-blind experiments...