Procedures like gastric bypass have been around a long time; long enough that their effects are measured by virtue of their impact on overall health. If your goal with weight loss is to lose weight, and not perform a ritual of self-actualization or make scientific discoveries, you should probably seriously consider it.

From wikipedia (emphasis added):

Long-term studies from 2009 show the procedures result in significant long-term loss of weight, recovery from diabetes, improvement in cardiovascular risk factors, and a mortality reduction from 40% to 23%.[12] A meta-analysis in 2021 found that bariatric surgery was associated with 59% and 30% reduction in all-cause mortality among obese adults with or without type 2 diabetes, respectively.[13] This meta-analysis also found that median life-expectancy was 9.3 years longer for obese adults with diabetes who received bariatric surgery as compared to routine (non-surgical) care, whereas the life expectancy gain was 5.1 years longer for obese adults without diabetes.[13] A 2013 National Institute of Health symposium summarizing available evidence found a 29% mortality reduction, a 10-year remission rate of type 2 diabetes of 36%, fewer cardiovascular events, and a lower rate of diabetes-related complications in a long-term, non-randomized, matched intervention 15–20 year follow-up study, the Swedish Obese Subjects Study.[14] The symposium also found similar results from a Utah study using more modern gastric bypass techniques, though the follow-up periods of the Utah studies are only up to seven years. While randomized controlled trials of bariatric surgery exist, they are limited by short follow-up periods. The risk of death in the period following surgery is less than 1 in 1,000.[15]

Yes, the above are observational studies, and they probably overestimate the benefits to some degree. Nevertheless, the proposed mechanism of action here seems so obvious, and the effect sizes are so large, that I think it's an overdetermined choice above a BMI of 35. The up-front payment and recovery periods are not a serious blocker for most people when compared against the reduced healthcare costs and QALYs, setting aside any social or romantic benefits of being thinner. 

I'm confused that surgery is not a more heavily discussed option for weight loss, given that it's the only thing that's been shown to reliably work. Most morbidly obese people in my social circle are programmer-adjacents who are desperate to lose weight and can afford the procedure. They are not the type of people to fall for some sort of naturalism bias, and they'd not indicated to me ever considering these options. I assumed they had good reasons for not doing so, and asked them about it. 

One of two things happened when I did:

  1. I had to explain away a mistaken impression that bariatric surgery was simply cosmetic, like liposuction. Liposuction, which is not bariatric surgery, removes fat from your body without fixing your appetite, so ceteris paribus you regain the weight later. Gastric bypass (in addition to other things) physically modifies your stomach so that your metabolic set point moves down.
  2. They told me that they thought that weight loss surgery was "cheating" and should be an absolute last resort. They seemed angry that I brought it up, not because I suggested they wanted to lose weight (this is a frequent conversation topic) but because they thought it sounded "weak".

To put it frankly, number two seems like a really stupid reason to kill yourself, and I'm curious if anybody in the comment sections has any actually good objections. I get the sense that some people feel a bizarre sort of shame about fixing this particular medical problem with medicine; possibly they anticipate that others will judge them if they spend a lot of money on a surgery that has a cosmetic component, also possibly they've invested so much mental or physical energy in pursuing weight loss that finishing they don't want to finish the journey in a narratively unsatisfying way. Regardless, those feelings should take a backseat to not dying at fifty of heart disease. There is basically one somewhat-consistently effective weight loss intervention and that's surgery. Not keto, not intermittent fasting. Even if diets worked, surgery seems plainly better to me than any diet, because it simply reduces your need for food instead of requiring you perform a sispyhian task of self-regulation.

If I had never tried to diet before, and I qualified for one of these surgeries, I would try to diet for six months, and then immediately attempt it if nothing worked. I've personally shed a lot of weight on a very-low-calorie rice diet in recent months, but if I rebound (as most people seem to do) I will try to convince a doctor to perform it, even if I'm under the normal weight of people undergoing gastric bypass. 

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It's been a while since I looked into weight loss surgery, but when I did the rate of complications was enormous. "People should treat this as a series of surgeries and consider themselves lucky if it only takes one" level. Even then it was still worth it at a certain risk level, and >35 may be the right cut-off. But the discussion feels incomplete without a hard look at the risks.


This source here suggests complication rates between 15 and 5 percent, readmission rates between 6 and 3 percent, and reoperation between 3.5 and 1.5 percent of the time, depending on the skill of the surgeon. Empirically, broad overall health outcomes improve, so while it'd be good to do a deeper dive on accidents, my prediction is that it will not change the calculus (except perhaps how much hard to look for good doctors).

Wait, do lesswrongers not know about semaglutide and tirzepatide yet? Why would anyone do something as extreme as bariatric surgery when tirzepatide patients lose pretty much the same amount of weight after a year as with the surgery?


Two things:

  • Sometimes semaglutide doesn't work
  • There's less information about it. I've heard lots of anecdotal reports of semaglutide inducing tolerance and losing its effects over time. If this means spending 2k/month forever to maintain the same weight then that's pretty bad.

Separate note, but I downvoted this post because it's unclear to me from reading the post that it justifies the strength of the claim title (or at least the strength of the claim as I interpret it). Rather than "Bariatric surgery seems like a no-brainer for most morbidly obese people", something like "Bariatric surgery recommended" or "Unclear why more people don't get bariatric surgery".

General anesthesia might be neurotoxic, which might permanently cost you IQ points due to brain damage. Surgery near vital organs always has a chance of killing you. Even if it doesn't, complications from botched surgery can permanently impair your quality of life, even past the point you might rather be dead.

Bariatric surgery should be seen as a last resort. Alternatives should be tried first. Unfortunately, modern diet advice seems to mostly not work for obese people. Fortunately, Semaglutide is now available and seems effective. The risks seem to be lower, but I'm mostly going off of base rates of drugs vs surgery and could change my mind with better data. This was a relatively recent development. There's a lot more research in progress that could bear fruit if one can afford to wait.

That said, a last resort is still a resort, and there has got to be some point where it wins a risk/benefit analysis, even given the best available knowledge. However, I don't trust doctors to understand statistics. BMI is statistically useful at a population level, but too imprecise to make this kind of decision. There are more informative tests that can give a more accurate sense of individual risk.

Liposuction is not just cosmetic, but counterproductive, because it removes not just fat, but fat storage capacity (i.e., adipose tissue). Overweight only becomes a serious health concern once fat storage capacity is exhausted, because then fat starts building up where it doesn't belong. How "fat" a person looks, how much they weigh, or their BMI doesn't account for this capacity, which varies quite dramatically with individual genetics. Again, these are useful measurements on a population level, where capacity averages out, but an "obese" person by BMI with capacity to spare is taking a bigger risk with surgery.

The mechanism of action for bariatric surgery was originally thought to be simply reduced stomach size causing reduced caloric intake, however, later research seems to indicate the mechanism of action is instead a change in gut flora.

Epistemic status: I am not a doctor or any other kind of medical expert. This has been a second-hand knowledge dump intended to be used as a starting point for further discussion or research, not as medical advice. I may be misremembering what I've heard, or those I've heard things from may have been ignorant or lying. I'm still confused about what caused the obesity epidemic, because there many plausible hypotheses.


General anesthesia might be neurotoxic, which might permanently cost you IQ points due to brain damage.

Sources on this? I'm not understanding if you're saying "sometimes general anaesthesia turns out to be neurotoxic" (which is reasonable, I know it can go awry in a number of ways, up to and including killing you) or "it is possible that general anaesthesia is always neurotoxic, and we just haven't figured it out for sure yet". The latter seems a pretty serious claim that I'd never heard before.

I can't recall the source I heard this from, sorry. It's been too long.

It might have been related to this issue:

Summarizing, animal models show the neurotoxicity of anesthetic drugs, particularly on developing brains. In humans that would be up to about 3 years old. I didn't remember that part, but I expect that candidates for bariatric surgery would be older than this. Also, humans have somewhat unusual brains as animals go, meaning the results might not generalize, and medical anesthesia appears to be more controlled than the animal experiments. The link cited a few studies in humans tempering the concern.

I also found this one: suggesting that postoperative delirium is due to the anesthesia itself, not the physiological stress of surgery, and side effects can persist for years. The elderly appear to be more at risk. But perhaps most candidates don't survive long enough to become elderly. I'm not sure of the age/obesity demographics.


Ah, thanks! I'm not sure if I should actually look too far into this rabbit hole or treat it as a infohazard since if I'll ever need general anesthesia it probably won't be like I'll have much choice, and if I can't do anything about it, I'd rather not have additional worries on top. I definitely already was of the opinion that I'd rather avoid it unless it's for something truly life-threatening, but that's just because surgery in general always comes with its own share of risks of either death or permanent side effects. I've had one total anesthesia surgery suggested for a problem that is merely quality of life, can be somewhat managed pharmacologically AND has a high relapse rates after a few years, plus the surgery itself has something like a 1/1000 or so risk of complications like blindness or death. My answer to that was "yeah no thanks". It's difficult to assess precisely risks when discussing with some doctors but I really don't see how that's a decent trade off.

I am a physician trained in bariatric surgery but do not do it as part of my practice. That being said, on a population level and until the recent introduction of the GLP drugs bariatric surgery is the only thing that actually results in long-term weight loss for morbidly obese people. It does, however, have significant risk of early and late complications and vastly changes behavior, which some people find it hard to deal with. Early complications include leak with about a 2% risk, death with about 1/500 or so, and various and sundry other minor complications that have a risk of about 10%.

I would absolutely undergo sleeve or bypass if my BMI went over 35 with any comorbidities if I did not get adequate results from the new GLP medications, which, in my opinion, should definitely be first line for people without contraindications.

I'm not sure it's so clear cut anymore thanks to the existence of semaglutide. It seems likely to provide better tradeoffs than surgery for weight loss.

(Not medical advice)

While most of these points are very good, there is a downside-for-many-people of gastric bypass in particular, that should be noted. Not only does it make you feel full sooner (good), but it drastically restricts the amount of food one can ever eat in one sitting/digestive cycle/whatever. Further details on this on the Mayo Clinic site.

Gastric bypass is still probably worth it for a lot of the people who'd do it. Just noting this.