One Anastomosis Gastric Bypass

What is a One Anastomosis Gastric Bypass?

One Anastomosis Gastric Bypass (OAGB), previously known as Mini Gastric Bypass, is a modern weight loss procedure that combines elements of both the Gastric Sleeve and the traditional Roux-en-Y Gastric Bypass.


The OAGB is a restrictive and malabsorptive operation, meaning it limits the volume of food that can be consumed while also reducing the absorption of calories and nutrients. This combination makes it a highly effective bariatric option with good weight loss outcomes and a positive impact on quality of life (Lee et al., 2014, Musella et al., 2016).


Who Is a Candidate?

OAGB may be suitable for individuals who:

  • Have a BMI ≥ 40, or ≥ 35 with obesity-related comorbidities such as type 2 diabetes, hypertension, or sleep apnoea (Angrisani et al., 2015; Rubino et al., 2016)
  • Have failed to achieve and maintain weight loss through conventional methods such as diet, exercise, behavioural modification, and pharmacotherapy (Dixon et al., 2012)
  • In selected cases, have a BMI < 35 but present with significant metabolic disease (e.g., type 2 diabetes, insulin resistance) where surgery may be beneficial based on clinical judgment (Schauer et al., 2017; ASMBS, 2019)


How is the Procedure Performed?

OAGB is performed laparoscopically (keyhole surgery) under general anaesthesia.


Key Steps:

  • Five small incisions (5–12mm) are made for access.
  • The upper stomach is divided to create a narrow tube-shaped pouch (approximately 30–50ml in volume).
  • This pouch is then connected to a loop of small intestine, bypassing the duodenum and approximately 150–200 cm of the small bowel.


The rest of the stomach and bypassed intestine remain in the body but are no longer involved in food digestion.


How Does OAGB Work?

OAGB facilitates weight loss through:

  1. Restriction: The creation of a small gastric pouch significantly limits the volume of food intake, helping patients consume smaller, more controlled portions (Lee et al., 2014; Musella et al., 2016).
  2. Malabsorption: By bypassing approximately 150–200 cm of the proximal small intestine, OAGB reduces the absorption of calories and nutrients, enhancing the overall weight loss effect (Robert et al., 2019; Rutledge & Walsh, 2005).


Expected Weight Loss

Most patients can expect to lose up to 70% of their excess body weight within 12 to 18 months following surgery (Lee et al., 2014, Musella et al., 2016).


Advantages of OAGB

  • OAGB is particularly effective for patients with a higher BMI, providing consistent and reliable long-term weight loss outcomes (Lee et al., 2014; Musella et al., 2016).
  • Many patients experience rapid improvement or complete remission of type 2 diabetes, often shortly after surgery, due to hormonal and metabolic changes induced by the procedure (Rubino et al., 2016; Schauer et al., 2017).
  • Unlike gastric banding, OAGB does not require ongoing adjustments or device management, simplifying postoperative care (Rutledge & Walsh, 2005).
  • The procedure discourages consumption of high-sugar and high-fat foods through the development of dumping syndrome, which produces unpleasant symptoms after ingesting such foods (Lee et al., 2014).
  • OAGB involves only one anastomosis (surgical connection) compared to Roux-en-Y gastric bypass, which has two; this can result in shorter operative times and potentially fewer surgical complications (Magouliotis et al., 2017; Robert et al., 2019).


Disadvantages

  • OAGB is a more complex procedure compared to purely restrictive surgeries and is associated with a higher risk of serious complications, although these remain relatively uncommon (Lee et al., 2014; Musella et al., 2016).
  • Due to its malabsorptive component, there is an increased likelihood of nutritional deficiencies, necessitating lifelong vitamin and mineral supplementation to prevent complications such as anemia, osteoporosis, and protein malnutrition (Rubino et al., 2016; Mechanick et al., 2013).
  • Regular, long-term follow-up with the surgical team and dietitians is essential to monitor nutritional status, adherence to supplementation, and to optimize sustained weight loss and health outcomes (ASMBS, 2019; Schauer et al., 2017).


Risks and Potential ComplicationsAcute Complications

  • Bleeding: Occurs in less than 1% of cases and may necessitate blood transfusion or, rarely, reoperation (Lee et al., 2014; Musella et al., 2016).
  • Infection: Postoperative infections can occur and typically require antibiotic treatment; severe cases may require surgical intervention (Rutledge & Walsh, 2005).
  • Anastomotic Leak: A serious but uncommon complication occurring in under 1% of patients, requiring urgent management due to risks of sepsis and prolonged hospitalization (Robert et al., 2019).
  • Ulcers: Marginal ulcers may develop at the site of the gastrojejunal anastomosis; routine postoperative use of anti-ulcer medication for at least six months is recommended to reduce this risk (Palanivelu et al., 2015).
  • Organ Injury: Though rare, inadvertent injury to adjacent organs during laparoscopic surgery may occur and sometimes requires additional surgical repair (Magouliotis et al., 2017).
  • Blood Clots: Deep venous thrombosis (DVT) and pulmonary embolism (PE) are recognized postoperative risks, with prophylactic measures employed to reduce incidence (Schauer et al., 2017).
  • Pneumonia or Chest Infection: Respiratory complications may develop postoperatively, particularly in patients with pre-existing pulmonary conditions (Mechanick et al., 2013).


Preventative strategies are employed to reduce these risks, including early mobilisation and prophylactic medications.


Long-Term Complications

  • Wound Hernia: Herniation can develop at incision sites postoperatively, sometimes necessitating surgical repair (Lee et al., 2014; Musella et al., 2016).
  • Anastomotic Stricture: Narrowing of the gastrojejunal anastomosis may occur, requiring endoscopic dilation to restore normal passage (Palanivelu et al., 2015).
  • Internal Hernia: Intestinal loops can become trapped internally, causing bowel obstruction that often requires prompt surgical correction (Magouliotis et al., 2017).
  • Adhesions: Formation of intra-abdominal scar tissue can lead to bowel obstruction or chronic pain (Schauer et al., 2017).
  • Gastroesophageal Reflux Disease (GERD): Reflux symptoms may persist or worsen postoperatively; OAGB is generally contraindicated in patients with severe pre-existing reflux (Robert et al., 2019).
  • Weight Regain or Inadequate Weight Loss: Frequently related to poor adherence to dietary and lifestyle recommendations following surgery (Rubino et al., 2016).
  • Severe Malnutrition: Rare but serious nutrient deficiencies may develop, sometimes necessitating intravenous nutritional support such as total parenteral nutrition (TPN) (Mechanick et al., 2013).


Dumping Syndrome

Dumping syndrome occurs when high-sugar or high-fat foods rapidly enter the small intestine, leading to a range of symptoms including nausea, abdominal cramping, dizziness, and fatigue (Lee et al., 2014; Mechanick et al., 2013). This condition acts as a natural deterrent against the consumption of unhealthy, calorie-dense foods (Rutledge & Walsh, 2005). Patients will receive dietary education and guidance to help minimize the risk and manage symptoms effectively (Palanivelu et al., 2015).


Pre-Operative Diet

Before surgery, patients follow a 14-day very-low-calorie diet, typically using Optifast™ meal replacements. This helps reduce liver size and improves surgical safety. Detailed instructions are provided by your dietitian.


Post-Operative CareHospital Stay

  • Usually 3–5 days
  • Clear fluids post-operatively, progressing gradually over 4–6 weeks


Post-Operative Imaging

  • An x-ray is performed to check for leaks and confirm pouch size


Diet Progression

  • Begins with fluids → pureed → soft foods → normal textured meals over weeks
  • A detailed dietary booklet is provided by the dietitian


Follow-Up CareSurgeon

  • First review at 1–3 weeks post-surgery, then periodically


Dietitian

  • Contact within the first week post-op
  • Regular follow-up at 3–6 weeks, then every 3–6 months


Long-term lifestyle changes and regular reviews are critical for lasting success.