- Less volume: you are full after a few bites.
- Less hunger: after a sleeve the hunger hormone ghrelin falls.
- Different gut hormones: after a bypass the set point shifts.
- Weight loss holds well for up to about ten years.
- Some weight returns after five to ten years; behaviour matters.
How does the operation work?
The operation is keyhole surgery under general anaesthesia through four or five small incisions. In a sleeve the surgeon removes about 75 to 80 percent of the stomach. In a bypass the surgeon creates a small stomach pouch and connects it to a lower part of the small intestine; the rest of the stomach stays in the abdomen but is no longer used.
Operation times range from 45 to 75 minutes for a sleeve to 90 to 120 minutes for a classic bypass, usually followed by a hospital stay of one to three nights.
Why you are less hungry: the hormones
It is a misconception that weight loss surgery only works because less food fits. After a sleeve, the part of the stomach that makes ghrelin, the hormone that drives hunger, is gone. After a bypass, food reaches the part of the intestine that releases satiety hormones sooner. WeightWorks describes this as shifting the set point: the weight your body steers towards. With type 2 diabetes, blood sugar therefore often improves before much weight has been lost.
How long does weight loss surgery work?
The fastest weight loss is in the first six to twelve months; after one and a half to two years weight stabilises. According to Prof. Luc Van Gaal (Antwerp University Hospital), weight loss holds well for up to about ten years; there is less data about the period after that. WeightWorks reports that after ten years more than 90 percent of bypass patients have lost at least half of their excess weight, and that most still have a healthy weight after twenty years.
Some weight returns after five to ten years. That happens gradually, not suddenly, and eating behaviour plays a big role: grazing, liquid calories and eating without hunger undermine the result.
What helps and what undermines the effect
Advantages
| Advantage | Explanation |
|---|---|
| Six small meals | prevents big hunger and eating too fast |
| Half an hour between eating and drinking | food is not flushed through |
| High-protein food | keeps muscle mass during weight loss |
| Keeping check-ups | deficiencies and relapse spotted early |
Points of attention
| Point of attention | Explanation |
|---|---|
| Grazing | eating small amounts all day |
| Liquid calories | soft drinks, juice and alcohol pass easily |
| Skipping check-ups | deficiencies go unnoticed |
| Eating without hunger | emotional eating often returns after year one |
Cost and insurance (2026)
What weight loss surgery costs depends on coverage. The way it works is the same whether covered or self-paid.
| Item | Amount or arrangement |
|---|---|
| With referral and indication | €385 deductible 2026 |
| Self-pay | about €7,000-€11,000 |
| Vitamins | about €10-€15 a month, for life |
How weight loss surgery works: key figures
| Feature | Value |
|---|---|
| Weight loss sleeve | about 20-30% of total weight |
| Weight loss bypass | about 30-40% of total weight |
| Fastest loss | first 6-12 months |
| Stabilisation | after 1.5-2 years |
| Effect holds well | up to about 10 years |
How the procedures work, side by side
| Procedure | Works through | Effect on hunger |
|---|---|---|
| Gastric sleeve | smaller stomach | less ghrelin |
| Gastric bypass | smaller stomach + bypass | different gut hormones |
| Mini bypass | stomach tube + one bypass | different gut hormones |
| Gastric band | restriction only | limited |
| Gastric balloon | temporary volume | limited, temporary |
Step by step
- Operation. Keyhole surgery of 45-120 minutes.
- Liquid. The first weeks liquid and puréed.
- Build-up. Step by step to solid food in small portions.
- Weight loss phase. Fastest loss in the first year.
- Stable. After about two years; check-ups for at least five.
Read next
- Types of weight loss surgery — all options
- The operation step by step — duration and risks
- Long-term risks — after ten years
- When the effect declines — revision surgery
Why diabetes often improves before weight loss
After a bypass, food reaches the part of the small intestine that releases hormones regulating blood sugar much sooner. That is why many people with type 2 diabetes need less medication within days, long before they have lost much weight. Vitalys calls the bypass the first choice with type 2 diabetes for this reason. Type 1 diabetes, however, is not cured by surgery.
Frequently asked questions about how weight loss surgery works
Your stomach becomes smaller, so you are full sooner, and your hormones change so you are less hungry. With a bypass, part of the intestine is also bypassed, which strengthens the effect on weight and blood sugar.
For most people weight loss holds well for up to about ten years. There is less data about the period after that. Some weight gradually returns after five to ten years, often because eating habits change.
Not by itself. The operation is a tool. If you let go of the new eating pattern you can regain weight, even with a small stomach. Losing it again is often possible but takes more focus.
Right after the operation you eat much smaller portions. The fastest weight loss is in the first six to twelve months. With type 2 diabetes, blood sugar can improve within days after a bypass.
Especially the bypass influences gut hormones that regulate blood sugar. Many people need less or no diabetes medication afterwards. This applies to type 2 diabetes, not type 1.
The stomach tube or pouch can hold somewhat more over the years, especially with large portions. Small portions and eating slowly help limit that.
After a sleeve the part of the stomach that makes the hunger hormone ghrelin is gone. After a bypass the gut hormones change. Hunger usually returns gradually during the first year.
It is keyhole surgery under anaesthesia through four or five small incisions. The surgeon reduces the stomach with staples and, with a bypass, also connects it to the small intestine. It takes 45 to 120 minutes.
A band only restricts the top of the stomach and hardly changes hormones. That is why it works less strongly and for a shorter time, and why it is rarely placed in the Netherlands anymore.
A balloon temporarily fills part of the stomach to create a full feeling and is removed after six to twelve months. Nothing permanent changes in the stomach or intestine.
Call +31 6 38048347 (Mon–Fri 09:00–17:00) or email info@maagverkleining-info.nl. This page is also available in Dutch.
Sources
- WeightWorks: gastric bypass and how weight loss surgery works
- Prof. Luc Van Gaal (Antwerp University Hospital): long-term results
- Vitalys (Rijnstate): FAQ
- Máxima MC: the operation
Search terms leading here: how does weight loss surgery work, how long does weight loss surgery last, how gastric bypass works, gastric sleeve hunger hormone.
Author: Gijs Bodenstaff. Last reviewed: September 2026.