Is the gallbladder really just a rudimental organ? If I undergo cholecystectomy, will my life expectancy be shorter than normal because of that?
This is very good and pragmatic question. I will answer no.
First of all, there are no studies to date which would have investigated the life expectancy after cholecystectomy. Of course this statement can be hardly profoundly backed up, but if you search PubMed with "cholecystectomy AND "life expectancy", none of the studies will look at this issue.
There is a NICE guideline and a recently published review article in NEJM, which does not take any stance about the long term disadvantages such as reduced life expectancy after cholecystectomy. Moreover, laparoscopic cholecystectomies have been performed since 1985 and open cholecystectomies since 1882. 700 000 cholecystectomies are performed annually only in the US.
Considering that cholecystectomies have been performed more than 130 years and the total number performed only in US is probably some where around +10 mil, I am fairly certain that if this operation would indeed have definitive adverse long term effects, they would have been even suggested if not partly shown by some investigator some where to date.
Finally, even tough some investigator would stated that cholecystectomy is associated to reduced life expectancy, according to Hill´s principles we should also be able to have some sort of plausibility in order to have causality between these two. I can´t up some up with reasonable plausibility at this moment....
It occurred to me after I wrote the initial response that life expectancy would be UNAFFECTED and would not show up in data per se, because of the life style implications. For example, higher consumption of sugar leads to a litany of health issues, of which problems with gall bladder is just one among many. So, a person that fits this bill has their gall bladder removed, their person life expectancy is not changed. Absent a lifestyle change, if they were going to live to be 70, after gall bladder surgery, they will still live to be 70. If you have a lower sugar consumption, and hence a healthier lifestyle (all things being equal), well, you were going to live longer anyway, and probably won't need your gall bladder removed. But if you did a data query on life expectancy and gall bladder removal it would be difficult to make a precise correlation that would not be directly associated with gall bladder removal, that couldn't be laid at the feet of just a general lifestyle issue.
Gary Taubes book, "Good calories, Bad calories" does a great job of exploring various fat/carb/protein hypotheses, and examines the science and history behind them. https://www.amazon.com/Good-Calories-Bad-Gary-Taubes-ebook/dp/B000UZNSC2/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1490886787&sr=1-1&keywords=good+calories+bad+calories+by+gary+taubes