• entries
  • comments
  • views

How does WLS actually work?



Today is my six weeks week out surgiversary. Happy six weeks to me. Not sure what the traditional gift for that milestone is. Protein shake, probably.


I lost no weight at all while away from the scale last week. I've lost only about 2 pounds in the last two weeks. This does not reflect my changing body, however, so I will ignore what the &#*%@ scale says. We are not required to wear our scale numbers on name-tags, after all. My clothes are getting looser and I feel *thinner*. I'm down 37 pounds from my pre-op and 18 pounds from op, which seems glacially slow to me, but it would, of course, seem amazing before surgery. I'm totally on-plan, getting all my protein and water, keeping carbs low, and eating between 500-800 calories a day, so I know I'm not doing anything wrong.


Today's topic: How does WLS actually work? 


WLS does a lot of weird things to your body, and scientists and surgeons only understand a little bit about the mechanisms that go on afterwards, apparently. I like to research this stuff because it's really fascinating how little we know about weight loss/gain, metabolism, nutrition, and how they all come together with WLS. Here's my understanding of the science, through the eyes of an English teacher, not a scientist. I've got some links here, and many are to boring medical study reports. Also, please note that this is a pretty new field of study, and there are many studies whose results don't agree with the below information. Science is pretty messy, and medical/nutritional science seems especially messy - it's full of complicated factors that are difficult to exactly reproduce, and clear answers don't come until studies can be reliably repeated with the same results. We're not there yet. Example: Here's a study laying out two opposing views and the research to back them up *warning: boring medical research paper*


Most people think that WLS is all about restriction, i.e. not allowing the body to eat much because of restricted stomach size (and for RNY/DS patients malabsorption, i.e. bypassing some of the intestine where nutrients are absorbed). Makes sense. However, researchers are finding that this only accounts for a small portion of the changes our bodies go through, and some good evidence comes from comparing sleeve and bypass patients with lapband patients: lapband patients don't experience the same metabolic changes as other WLS patients. For the purposes of the rest of this post, when I use "WLS" I'm not referring to lapband because lapband patients don't see these effects. (Sorry, lapband people. I know there are many people who enjoy successful lapband experiences, but they apparently aren't successful for these particular reasons!)


Hormonal changes


One effect of WLS: a decrease in several key hormones that deal with metabolism: insulin, leptin, ghrelin, and chemerin (well, and like 40 others, but I've found less info on them). Insulin regulates blood sugar and how cells either use or store glucose (sugar) from food we eat. Leptin is secreted by fat cells and is responsible for making you feel full after you eat. Ghrelin is secreted and makes you feel hungry when your stomach is empty, and secretion stops when your stomach is full. Chemerin plays a role in insulin resistance and breakdown of fats. These hormones get thrown out of whack by obesity. Or hormones being out of whack causes obesity. Researchers are not sure. Being out of whack and obesity go hand in hand, anyway. They should be self-regulating: more food makes you feel full, increased body fat makes you want to eat less, etc. However, with "metabolic syndrome" all of this is messed up. Fat people crave more food, not less - not because they're gluttons, but because they are driven to by their out of whack hormones. This is part of why even successful dieters usually gain weight back - their hormones are still messed up and drive them to eat.


RNY and sleeve operations seem to fix this, or reverse it, and it's not entirely clear why. This is connected to the reasons that most patients with diabetes go into remission in after surgery - the body just suddenly gets better at dealing with blood sugar regulation because insulin secretion has been changed. This happens before patients actually lose much/any weight - so it's not a result of weight loss, but the surgical changes to the GI tract. This is also connected to why most patients don't feel hungry after surgery (at least initially) - the ghrelin is not being secreted as before (besides that stomach nerves are healing!). 


Microbiome changes


Another effect of weight loss surgery is a change in the gut bacteria in the patients' intestines. This bacteria, known as the "microbiome," may play a large role in weight regulation as well as many other body regulation systems, but the research on this is fairly new. Doctors can "transplant"* microbiome from a healthy person to someone with an unhealthy imbalance (such as a Clostridium difficile infection, which causes horrible diarrhea and colon damage) and the transplanted microbiome will take over and fix the problem. In doing these, doctors noticed that if the "donor" suffered from obesity, the patient receiving the transplant might also begin to suffer from obesity. The different varieties of bacteria in the microbiome can lead to leanness or obesity. Studies of the microbiota of WLS patients show that the varieties of bacteria change after the surgery and the new microbiota show a larger number of varieties. In fact, in lab studies, researchers have been able to take rats who've had gastric bypass surgery (poor little rats!) and transplant their microbiota to obese rats and the obese rats lose weight! 

*if you are interested in how a transplant might work, and you have a strong stomach, here you go. There are also capsules that have been developed...


Resting Metabolic Rate changes


A huge problem when undergoing weight loss is that the the patient's metabolism adapts (slows down) as weight is lost. This is because the body wants to preserve the status quo - in evolutionary terms, it's a good idea to respond to famine by hanging onto weight instead of losing it. Unfortunately, we can't tell our bodies that they're not experiencing famine - just trying to lose weight! From the studies that I can find, it seems that WLS patients experience a less severe experience with this, or perhaps their RMR improves. In a study comparing Biggest Loser competitors with RNY patients, the resting metabolic rate of the RNY patients was higher - they were burning more calories per day - than the Biggest Loser competitors at one year out, even though the Biggest Loser competitors lost less lean mass or gained more muscle than the RNY patients. (The authors of that study see merit in eating lots of protein and exercising to help out with this) The science is not totally settled on this as studying it is difficult due to many factors that can confuse the results.


Anyway, there are probably other mechanisms I haven't read about (reminder: I'm not a scientist!), and there are undoubtedly mechanisms researchers haven't identified yet, but this is a basic overview of the less obvious ways that WLS helps us lose weight. I'm pretty sick of reading the "calories in calories out" stuff that's out there - it's just not a complete way of thinking about how people lose or gain weight. 


Here are some more "fun" articles (non medical journals) if you're interested: 

Why You Can't Lose Weight on a Diet (nytimes) 

After "The Biggest Loser" Their Bodies Fought to Regain Weight (nytimes)

Bacteria in the Intestines May Help Tip the Bathroom Scale, Studies Show (nytimes)

Woman Becomes Overweight After Fecal Transplant from Overweight Donor (iflscience)

Most of Us Misunderstand Metabolism. Here are 9 Facts to Clear That Up (vox)

When You Lose Weight, Where Does It Go? (Scientific American) - lots of scientific jargon, but short









Recommended Comments

Really great read! Thanks for summarizing. I read that Biggest Loser article a while back. Such a depressing read. And one reason I'm choosing to have WLS.

Share this comment

Link to comment

Thanks - I spend a lot of time reading up on this stuff, so it was helpful to me to put it all in one place. I hope it may be of help to others when they're making this decision. I have to say that the article on BL was a major push for me - if these people can't do it, how could I??? Super depressing. 

On the positive side, I'm hoping that my WLS will be the tool that I need to get me where I want to be. So far, so good! And good luck on your surgery - the feeling I got when I finally made the decision to go for it was such a relief. You're in for a ride, but a manageable one :)

Share this comment

Link to comment

I've looked at all these kinds of studies over the years and get very annoyed by the calories in calories out advocates. It might make sense if all calories were indeed equal, but it doesn't take much to realise they aren't. When anyone brings that old standard into conversation I just laugh and suggest they do more homework before they spout that rubbish again. Said with conviction it tends to shut them up I find, and I don't even have to explain.

Share this comment

Link to comment

@Aussie H It's like thin people think they are subconscious math geniuses, always eating the EXACT amount of calories every day that they need to in order to not gain weight (it should only take an extra 95 calories per day for a year to gain 10 pounds!). Little more complicated than that. I like your response. I'll have to remember that :)


Share this comment

Link to comment

Exactly. I've also been fascinated by some of the not so thin people who like to comment that I'm getting too skinny. What a joke. I tell them I am still "obese" and they don't believe me. It isn't hard to see the fat especially since we are still coming out of summer in Australia, so still shorts weather especially where I live. The problem they seem to have is that I'm now smaller than they are. To accept that I'm still obese means accepting that they are.

I don't count calories and won't be. I find logging everything I eat makes me become obsessive about food and that becomes depressing and makes me very aware I'm depriving myself. I do watch out when it comes to carbs but even then I don't actually track them. I want this journey to be more about mindful eating than about tracking every little thing. So far it's working for me, if it ceases to then I'll look at tracking things for a while. I just don't want the rest of my life to be me being on a diet. 

Share this comment

Link to comment

I hear you on the "concerned" friends. Being a fat person and confronted with someone else's weight loss is hard, so it's not surprising they respond with a push-back, but it sure does make them difficult to listen to. I lost quite a lot of weight about a decade ago and experienced that myself from a few people (...and gained it all back plus a lot, which is why I'm here, of course). 

It sounds like you have a healthy attitude toward food intake - good for you :) I tend to obsess over data of all kinds, so I'm a tracker, but may give that a break once I find a routine (early days for me still - want to make sure I'm getting my protein, etc). 


Share this comment

Link to comment

I haven't had a chance to read the fecal transplant articles but from this little I know about this topic, it fascinates me. There is a fecal lab near my home and I tried to volunteer my poop because I find gross things super cool. Alas, I was rejected and have never gotten over it. :rolleyes:

Share this comment

Link to comment

The microbiome stuff is fascinating... but it is possible that the weight loss is due to many things all at once, and I doubt just the microbiome changes account for all the weight loss. Sometimes people who are brilliant scientists in one arena are (in other areas) just well read and can over-interpret their data. 

Share this comment

Link to comment

Ah no, the other way around.  The human microbiome science is usually associative and the conclusion is that it is causative when it might not be ... With humans the science is not experimental. (e.g. it is hard to do sham bariatric surgery on people, like you might in rats, and then look at the differences between real and sham surgery; no doubt people would complain).

I agree that the work done in mice is more conclusive! but ... the last time I was a mouse it was 6 lives ago. :) More seriously the mouse experiments are done with genetically identical mice, for example, to reduce variability, but WLS is done in people with a lot of background genetic variance. Plus age differences. Plus dietary differences. Plus... and the list goes on. 


Share this comment

Link to comment

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now