Why so much variation in pre-op diets?

I'm curious if anyone knows why there's so much variation in pre-op diets between surgeons. It seems to vary more by surgeon than by patient or surgery type. When I was originally scheduled to have VSG in 2012 (which ultimately didn't pan out), my doc prescribed no pre-op diet at all. For my RNY next month, I have to stick to a high-protein, low-carb diet of meat and vegetables and cottage cheese (very similar to post-op) for 1-2 weeks. Then I read about people on month-long liquid diets that sound downright miserable! Why is there so much variation?

Surgeons have their own ideas of what they believe works best for their patients, usually based on their past experiences.  There's no guideline published on post op dietary considerations.  The best advice is to follow your surgeon's plan.

My surgeon varies his pre-op protocol based on Surgery type and patient's medical condition.

If he suspects fatty liver, he requires more of a pre-op regimen ---

Some feel that a strict pre-op diet helps to shrink the liver -- others think it makes little difference.

In my case, with no indication of fatty liver, my doctor preferred to have a well-nourished, well-hydrated patient on the morning of surgery.

I wondered that myself. My surgeon didn't prescribe a pre-op diet either.

My opinion, pre and post diets are detailed more by ancillary staffing...nutritionist.  There are few physicians that do surgery and focus on diet too.  I am sure there are clinics with very hands-on physicians and maybe they are well versed in dietary needs of the bariatric patient.  In my research, I did not find a clinic that staffed less than 2-3 nutritionist for 4-6 doctors in surgical group.  Just my experience.

It is just surgeon preference based on the surgeon's individual experience, overall medical approach, and belief about the value of pre-op diets.  

Some surgeons believe that a 2-week liquid diet will shrink the liver (which makes it easier to do the surgery - since the liver has to be lifted up out of the way).  Accidentally nicking the liver can be a serious surgical complication. Other surgeons don't believe that, for someone who has been MO/SMO for years, a 2 week liquid diet results in any significant liver reduction.  Some of those therefore require a 4-week pre-op diet to accomplish the liver reduction they are looking for.

If the surgeon -- like mine -- doesn't believe in liver reduction can be accomplished in only 2 weeks, or is planning an open surgery (in which the liver doesn't pose as much of a problem as in laparoscopic surgery), (s)he may prefer that patients be as strong as possible at the time of surgery and don't want patients to go into surgery with their body already being under stress from a drastic pre-op diet.

Some surgeons don't even base it on either of the above things; they just want patients to start their carb detox before surgery rather than after.

Lora