How does bariatric or bypass surgery change your body to help you lose weight? Is it just a smaller stomach so you eat less? In short the answer is hunger hormones!

I’ve been looking forward to writing this post, and I am very excited to share some knowledge about the hormones in our bodies that affect our appetite.

Before I started my own journey with weight loss surgery, I like many others, thought surgery was successful because mechanically you have a smaller stomach and you eat less – therefore you lose weight. Something I feared about having surgery was the crushing hunger pain I had pre-op would continue after, and I wouldn’t be able to eat enough to satisfy the perceived need. After experiencing a drug called Saxenda and researching more about hunger hormones I realized that surgery itself, and the subsequent weight loss has a huge affect on appetite regulating hormones, thus taking away my fear of feeling forever hungry.

First a few definitions….

Roux-en-Y Gastric Bypass (RYGB) makes up 70-75% of bariatric surgical procedures. This is the procedure I had, and for the purposes of this post I will focus mainly on how hormones are affected in this procedure. This is how the RYGB procedure works….


Glucagon-like peptide – 1 (GLP-1) is secreted from the distal ileum and colon in response to food intake. This hormone regulates your appetite by reducing hunger and increasing satiety. Some of the functions GLP-1 is responsible for are :

  • Slowing gastric emptying of food into small bowel
  • Promoting insulin release
  • Inhibits glucagon secretion
  • Inhibits gastric acids secretion
  • and Works on the nervous system to induce satiety – therefore decreasing food intake (feeling full)

GLP-1 is like a brake mechanism that helps your body regulate the movement of food through the GI tract.

But how does GLP-1 change after RYGB surgery?

Studies show that levels of GLP-1 are much higher in patients after RYGB when compared to the same patient before surgery and other normal weight patients. The reasoning for this is thought to be related to the speed at which food enters the small bowel (GLP-1 is released) after surgery. With higher levels of GLP-1 your hunger cues will be lessened and you will feel full sooner.


This is a perfect time to talk about Saxenda. The generic name for this drug is Liraglutide. This drug mimics GLP-1 so by giving a daily dose, hunger will be decreased, as well, insulin availability and sensitivity which are both increased. Saxenda is injected subcutaneously and is approved in Canada for use in type II diabetes. I will definitely discuss my experience with Saxenda in a later post – I wanted to loop it in with the hormone it most mimics for future reference.


Peptide tyrosine-tyrosine (PYY) is also secreted from the distal ileum and colon but only AFTER a meal. Like GLP-1 this hormone promotes satiety, delays gastric emptying and inhibits gastric acid secretion.

But how does PYY change after RYGB surgery?

Again, like GLP-1, levels of PYY measured in persons after RYGB surgery are higher than those pre-surgical or in other types of bariatric procedures. Food will enter the lower GI tract faster post operatively, therefore the theory is PYY levels are increased.


Leptin is secreted from fat cells and influences appetite by acting on the hypothalamus in the brain. Leptin signals the hypothalamus to decrease food intake and increase energy expenditure. The amount of Leptin circulating in the body is in proportion with the amount of fat cells one has.

So wait? Did I just say that the MORE fat cells you have the MORE leptin you should make? How does that make sense in obesity?

Progression of obesity is thought to be a product of leptin resistance rather than a deficiency of leptin. That explains how more fat cells = more leptin , but if the body is resistant to the leptin it will not reduce food intake.

Sleep is also really important for the regulation of leptin. The less sleep you get the less leptin you will produce – leading to more of an appetite and increased food intake.

But how does Leptin change after RYGB surgery?

Unfortunately the results of a scientific review were not consistent in regards to how leptin changes after RGYB surgery. The working theory is weight loss increases the body’s acceptance of leptin and decreases resistance, but this is a hard process to measure.


Last, but certainly not least is Ghrelin. Ghrelin is a little different from the first 3 hormones discussed. While GLP-1, PYY and leptin induce satiety or fullness – ghrelin tells your body its hungry!

Ghrelin is released from both the pituitary gland in the brain and from the lower part of the stomach. It’s main job is to stimulate appetite, telling the body to take in food/energy when the body is in a negative energy balance (eg. in a fasting state or during a restrictive diet). As you can imagine this is an evolutionary protective measure to keep us from starving to death. However in obesity, studies show that eating food, or the intake of energy does not suppress the action of ghrelin.

Sleep is also an important factor for ghrelin regulation. I use this fact all the time when talking to teens about sleep hygiene, and the importance of a good nights sleep. The less sleep you get the MORE ghrelin you release – therefore sleepless nights can lead to a higher hunger drive and more food intake.

But how does Ghrelin change after RYGB surgery?

Ghrelin is significantly lower post operatively and sustained at a lower level for up to a year post op. It is most likely that ghrelin is suppressed because the area where it is released (the lower stomach) is bypassed in RYGB and no food comes into contact with that area. So overall your hunger drive is turned WAY down after RYGB surgery.

So, what has been my experience so far?

As of today I am 3 weeks out from my RYGB surgery and down 30.4 lb since my pre op diet began. To say I have’t felt hunger in 3 weeks would be absolutely true. I know as time goes on, my new stomach gets used to “real” food (not liquid or puree) that some of those hunger hormones will change further.

While my hunger cues have changed significantly, so have my full cues. Big porition sizes were truly my downfall pre operatively but that was alongside extreme hunger (headaches, stomach pain, nausea). I know that what I was eating and how much all played a big role in that hunger but the point I’m trying to make is – I remember the hunger more than the fullness. Feeling full was usually a huge over exageration on the other end of things – feeling STUFFED, over eating. Now, I eat very slowly (1 tsp of food every 5 minutes) and usually around the 40-45 minute mark I start feeling like I need to burp. This is what I am now calling my fullness cue. Again, I’m sure that will changes as my intake/diet changes but I will just continue to listen to my body!

Thank you for taking the time to read this post. All of the information was from a review written by Beckman et al. (2010). If you have any questions at all – or anything you would like to comment on – please leave a public comment or use the contact me page to reach out!



Beckman et al. (2010). Changes in gastrointestinal hormones and leptin after roux-en-y gastric bypass procedure: A review. J. Am Diet Assoc. 110(4); 571-584

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