The main reason is that while the size of your new stomach plays a role in how hungry and full you feel, it’s not the star of the show. Instead, just like mood, sleep, heart rate, reproduction, and more, hormones take the lead in determining how full and hungry you feel. Changes in these hormones after surgery differ from person to person, as we talked about in our article about factors other than behaviors that influence your weight after WLS. The hormonal changes are a bit complex, so we’ll touch on the basics here and point you to where you can find out more.
The Hunger Hormone – Ghrelin
Ghrelin is the hormone that our bodies make to tell our brains that we’re hungry, and it’s often the one that gets talked about the most as a mechanism for weight loss after WLS. Ghrelin is produced in the stomach and stimulates hunger, fat deposition, and the release of growth hormone, among other things. With both the gastric bypass and gastric sleeve, reducing the size of the stomach also reduces the amount of ghrelin thus reducing hunger. During weight loss without surgery, the body produces more ghrelin to try to prevent weight loss. By reducing ghrelin, the surgery overrides the body’s desire to keep weight on. Much like before surgery, ghrelin levels and hunger will still vary from person to person after surgery. This is also true for the factors that lead to satiety.
Satiety after WLS
By having a small pouch for a stomach, food enters your intestine pretty quickly after WLS. This causes your body to produce an exaggerated amount of hormones from your gut that make you feel full. One of these hormones is glucagon-like peptide-1 (GLP-1). For people that don’t have the expected response to bariatric surgery and still feel hunger, there is research into using medications involving GLP-1 to improve satiety and weight loss.
Another hormone involved in satiety is leptin. Leptin tells your brain that you’re full, but some people don’t produce enough of it. Also, many people that have obesity have developed a resistance to it, so even if the body makes enough, the signal isn’t getting to the brain. Thinking you haven’t eaten, the body then produces more ghrelin to tell you to eat more. But after WLS, the body produces more leptin than it did before which is great if you don’t have resistance to it. If you do have resistance, having less ghrelin after surgery means that you can override the leptin resistance.
There is much more involved in hunger, satiety, and even the food you crave after WLS, and researchers still don’t fully understand a lot of it. If you like the science and biology of what’s happening in your body, check out the Food Intake and Eating Behaviour after Bariatric Surgery article from 2018. It discusses the interactions of the different changes in your body that promote weight loss after bariatric surgery. Like we said before, it’s about far more than just a smaller stomach.