Hormonal changes after gastric sleeve surgery are significant, wide-ranging, and often surprising. Most people go into surgery focused on the mechanical changes: smaller stomach, reduced appetite, weight loss. The hormonal picture is more complex than that, and understanding it helps explain many of the physical and emotional experiences that come with recovery and long-term life after surgery.
Ghrelin: the hunger hormone
The most well-known hormonal change after gastric sleeve surgery involves ghrelin. Ghrelin is produced primarily in the fundus of the stomach, the rounded upper portion that is removed during the procedure. Because much of the ghrelin-producing tissue is taken away, levels of this appetite-stimulating hormone drop significantly after surgery.
This is one of the key mechanisms that makes gastric sleeve effective beyond pure physical restriction. The dramatically reduced appetite that most people experience in the first year is substantially driven by lower ghrelin rather than just stomach size. Many people describe being surprised that they are not hungry in the way they expected, particularly in the early months.
Ghrelin levels do tend to rise gradually over the following years as the body adapts and the remaining stomach tissue compensates to some degree. This is part of why hunger typically increases in year two and beyond compared to year one, and why continued attention to diet and habits remains important even when the restriction feels less pronounced.
Insulin and blood sugar regulation
One of the most remarkable early changes after gastric sleeve surgery is in blood sugar regulation and insulin sensitivity. For James, whose pre-diabetic markers and metabolic risk had been building for years alongside his non-alcoholic fatty liver disease, the improvement in insulin sensitivity was rapid and significant.
Within weeks of surgery, before major weight loss has occurred, blood sugar regulation typically improves substantially. This happens faster than can be explained by weight loss alone and points to direct hormonal and metabolic effects of the surgery rather than purely the mechanical restriction. The improvement in type 2 diabetes and pre-diabetic states after bariatric surgery is one of the most robust findings in the surgical literature.
Sex hormones
Adipose tissue, fat, is hormonally active. It produces oestrogen, among other hormones, and in larger quantities stores and releases various hormones. As fat tissue reduces significantly and rapidly after gastric sleeve surgery, the hormonal landscape changes substantially.
For women, menstrual cycles often become more regular after surgery, particularly in those who had irregular periods related to conditions like PCOS. Fertility can increase significantly. This is important practically: the risk of unplanned pregnancy rises after bariatric surgery, and the first 12 to 18 months post-surgery is not recommended as a time to become pregnant due to the nutritional demands of rapid weight loss. Effective contraception in this window is essential.
For men, testosterone levels often improve as weight is lost, since excess adipose tissue is associated with lower testosterone. Improved energy, mood, and libido can follow.
Thyroid hormones
The relationship between weight loss and thyroid function is complex. Some people find that thyroid medication doses need adjustment after significant weight loss, as the dose prescribed at a higher weight may be too high for their new body weight. If you are on thyroid medication, regular monitoring and communication with your GP is important during the weight loss phase.
Stress hormones and mood
Cortisol, the primary stress hormone, is affected by both the physical stress of surgery and the rapid hormonal changes that accompany major weight loss. Elevated cortisol can contribute to the mood changes, irritability, and low mood that many people experience in the early post-operative weeks.
As fat cells shrink and release stored hormones into the bloodstream, this creates a temporary hormonal flux that affects mood in unpredictable ways. Some people feel euphoric. Others feel flat or emotionally volatile. Both are documented responses. Understanding that this is hormonally driven rather than a sign of psychological crisis makes it easier to manage.
Long-term hormonal health
Two years on, our hormonal health has stabilised considerably compared to the first year. The dramatic changes of early weight loss have settled into a new baseline. Blood sugar regulation is consistently better. Energy levels and mood are more stable. The hormonal chaos of early recovery has resolved into something much more manageable.
Regular blood testing, including thyroid function and relevant sex hormones where appropriate, remains part of ongoing monitoring. Hormonal health after gastric sleeve surgery is not something that can be assumed to take care of itself.
Sources
British Obesity and Metabolic Surgery Society (BOMSS): Clinical guidelines. Peterli et al: Improvement in glucose metabolism after bariatric surgery. NHS: Hormones. NHS: PCOS and weight loss surgery.
About this content
This blog is written by James and Kirsten, a couple from the UK who had gastric sleeve surgery together in March 2024.
We started this blog because we couldn't find any sources of content that details before surgery, the surgery and then life post surgery - so we decided to write one ourselves.
Everything on this site is based on our own experience and the research we have done along the way. It is not medical advice. Gastric sleeve surgery is a serious procedure and every patient's journey is different. Please always consult your own bariatric team or GP before making any decisions about your health or treatment.
Some posts on this site may contain featured or sponsored content, or affiliate links. Where this is the case, it will always be clearly stated at the top of the article. Our opinions are always our own.
Publish Date: 17 April 2026 | Last Reviewed: 7 June 2026 | Next Planned Review: 7 December 2027