The One Anastomosis Gastric Bypass (OAGB), historically also known as the mini gastric bypass, is a metabolic and bariatric procedure combining gastric restriction with an intestinal bypass component.

Its main advantage is its ability to achieve substantial and sustained weight loss, making it particularly attractive for patients with higher BMI, severe obesity or inadequate results following previous bariatric surgery.

Particularly effective for patients with a high BMI

In patients with severe obesity, particularly those with a BMI ≥50 kg/m², OAGB can provide greater weight loss than sleeve gastrectomy.

A recent systematic review in this population reported approximately 37% total weight loss at one year, with excess weight loss around 68%.

Comparative meta-analysis in patients with BMI >50 has also demonstrated significantly greater total and excess weight loss following OAGB compared with sleeve gastrectomy.

For this reason, OAGB can be an excellent option when a more powerful metabolic and weight-loss procedure is required.

How does OAGB work?

During the procedure, a long, narrow gastric pouch is created and connected to the small intestine using a single gastrojejunal anastomosis.

The operation therefore combines two mechanisms:

Restriction: the smaller gastric pouch reduces food capacity.

Metabolic and intestinal effects: bypassing part of the proximal small bowel modifies nutrient absorption and several hormonal pathways involved in appetite, satiety and metabolism.

This combination explains why OAGB can achieve greater weight loss than purely restrictive procedures such as sleeve gastrectomy.

Who may benefit most?

OAGB can be particularly attractive for:

Patients with a very high BMI
when greater weight loss is required than would typically be expected after sleeve gastrectomy.

Patients with weight regain after sleeve gastrectomy
where initial weight loss has been inadequate or significant weight has subsequently been regained.

Patients with significant metabolic disease
where a stronger metabolic effect is desirable.

Patients requiring revisional bariatric surgery
after an unsuccessful previous bariatric procedure.

An excellent revisional option after failed sleeve gastrectomy

OAGB is increasingly used in patients who have previously undergone a sleeve gastrectomy but subsequently develop:

• significant weight regain;

• insufficient initial weight loss;

• persistent severe obesity;

• or recurrence of obesity-related metabolic disease.

Converting a sleeve to an OAGB adds a powerful intestinal and metabolic component to the existing restriction.

A systematic review including more than 1,000 patients undergoing conversion from sleeve gastrectomy to OAGB reported approximately 65% excess weight loss at one year, increasing to around 71% at longer follow-up.

Comparative studies also suggest that OAGB may achieve greater weight loss than Roux-en-Y gastric bypass when used as revisional surgery after sleeve gastrectomy, although the choice of procedure should always be individualised, particularly in patients with significant reflux disease.

Long-term weight-loss results

Long-term outcomes are encouraging.

Recent systematic reviews report approximately:

33% total body weight loss
74–75% excess weight loss

at five years following OAGB.

OAGB can also produce substantial improvement or remission of obesity-related conditions including type 2 diabetes, hypertension, obstructive sleep apnoea and dyslipidaemia.

Powerful treatment requires careful follow-up

The greater metabolic effect of OAGB also means that lifelong nutritional monitoring is essential.

Potential long-term complications include:

• iron, vitamin B12, folate and micronutrient deficiencies;

• anaemia;

• protein malnutrition in a minority of patients;

• marginal ulceration;

• and bile reflux.

Appropriate patient selection, tailoring of bypass length and structured long-term follow-up are therefore fundamental. Current international position statements recognise OAGB as an effective primary and revisional bariatric procedure while emphasising nutritional surveillance and appropriate patient selection.