This involves placement of an adjustable ring-shaped device at the top of the stomach. Such a procedure can help regulate hunger but often results in food intolerances and reflux of swallowed food together with stomach acid back into the throat, if it is overtightened.

This procedure removes over 85% of the stomach, turning it from a volume of about 1.5 litres to the size and shape of a banana, with an initial volume of approximately 120-150 mL. The remaining smaller stomach leads to faster gastric emptying, which changes small bowel function and prolongs appetite control after a meal. Reducing the ability to mix acid with food means that minerals (iron, calcium, magnesium etc) and some vitamins (vitamin B12, folate, thiamine and others) will not be absorbed well and need to be supplemented.

Roux-en-Y Bypass (RYGB); Single Anastomosis bypass, Omega Loop bypass (OAGB) or Mini Gastric Bypass (MGB). All these operations involve bypassing at least 95% of the stomach, creating a sleeve-like stomach that is about half the size or less than a laparoscopic sleeve gastrectomy; combined with a bypass of a variable portion of the small bowel. The more that small bowel is bypassed with surgery, the easier it may be to lose weight; however, it is also the more likely to cause malabsorption and diarrhoea. Most commonly, a 1-2-metre segment of the small bowel is bypassed. All patients who have had a bypass operation require lifelong vitamin and mineral supplementation regardless of their diet quality, to help them avoid illness from malnutrition.

The Loop Duodenal Switch or SADI (Single Anastomosis Duodenal–Ileal Bypass with Sleeve Gastrectomy)/SIPS (Stomach Intestinal Pylorus Sparing) is the most common version, but there are others include the SASI (Single Anastomosis Stomach–Ileal Bypass with Sleeve Gastrectomy) and Transit Bipartition surgeries. These operations involve the combination of a Sleeve Gastrectomy with bypass of between one-half and two-thirds of the small bowel. Patients having longer bypasses are likely to run into nutritional problems if they don’t take more complex vitamin and mineral supplementation following surgery, while patients with shorter bypasses will often be satisfactory with simpler supplements.

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