Gastric bypass

What is gastric bypass surgery?

A gastric bypass is a type of bariatric (weight loss) surgery that works in two ways:

• Restriction: Your stomach is made much smaller, so you feel full after a few bites.
• Malabsorption: Part of your small bowel is bypassed, so you absorb fewer calories and nutrients.

Together, these changes help you lose weight and improve obesity related health conditions. Your hunger and blood-sugar hormones will also start to behave differently (in a good way).

What health conditions can improve after gastric bypass surgery?

Patients may see improvements in the following health conditions:

• Type 2 diabetes
• High blood pressure
• High cholesterol
• Obstructive sleep apnoea
• Fatty liver disease (NAFLD/NASH)
• Breathing problems
• Joint pain and mobility issues
• Heart disease risk factors.

What are the different types of gastric bypass surgery?

Roux-en-Y gastric bypass (RYGB)
This is the most common type. A small stomach pouch is created and connected to the small bowel in a Y-shaped formation.

One anastomosis gastric bypass (OAGB/mini gastric bypass)
This involves creating a small stomach pouch and attaching it to the bowel in a single join. It works similarly to RYGB, but it’s not suitable for everyone. Your surgeon will assess whether OAGB is appropriate based on your body anatomy, reflux history and long-term risk profile.

Who is suitable for gastric bypass surgery?

Suitability is usually based on your body mass index (BMI) and overall health.

You may be considered if:

• Your BMI is over 40, otherwise known as morbidly obese. Surgery may help you achieve long-term weight loss.
• Your BMI is over 35 and you have a weight-related condition (e.g., Type 2 diabetes, high blood pressure, sleep apnoea). Surgery may be recommended in this case.

If your BMI is over 30, lifestyle changes are usually recommended first.

Your surgeon will confirm your BMI and carry out a detailed assessment, including your medical history and your motivation to follow a long-term eating and exercise plan.

Who may not be suitable? You may be advised to delay or avoid surgery if you:

• Have severe heart or lung disease
• Have untreated mental health conditions or eating disorders
• Are pregnant
• Cannot commit to lifelong vitamin supplements.

What are the alternatives to gastric bypass surgery?

Lifestyle changes: Eating less or practicing portion control, improving your diet and increasing exercise remain the foundation of weight management. Your GP may also prescribe medication.

Other surgical options include:

• Gastric sleeve: Involves removing part of the stomach to create a narrow tube.
• Gastric balloon: A temporary balloon is placed in the stomach for 6–12 months.

A gastric balloon is non-surgical but offers less in terms of weight loss, and it’s seen as a temporary solution. It has limited benefit for adults with a high BMI.

Gastric bypass vs gastric sleeve: what’s the difference?

A gastric sleeve reduces stomach size but does not bypass the bowel. A gastric bypass reduces stomach size and reroutes the bowel. Bypass tends to produce slightly greater weight loss and better diabetes improvement.

How can I prepare for gastric bypass surgery?

Your consultation
You’ll meet with your surgeon and specialist team to discuss your medical history, weight-loss goals, and suitability. You may also meet a dietitian and psychologist.

Preoperative diet
Your surgeon will give you a specific low-calorie diet for 2 weeks before surgery. This reduces the fat content of your liver, making keyhole surgery safer.

Medication
It’s important to inform your surgeon and specialist team about all your medications, including:

• Blood thinners
• Herbal remedies
• Supplements
• Over-the-counter medicines.

For a few weeks after surgery, you may need liquid medication or crushed tablets because your bowel may absorb medicines differently compared to before the procedure. However, most patients can continue to have medications as normal.

Exercise
Regular exercise helps prepare your body for surgery and supports long-term weight loss. Your specialist team may give you tailored advice if you have other health conditions.

Reducing infection risk

• Don’t shave or wax the surgical area for a week before surgery
• Shower the day before or on the day of surgery
• Keep warm around the time of the operation
• Keep blood sugar controlled if diabetic
• Wash your hands regularly and wear a face covering if asked.

What happens during gastric bypass surgery?

Gastric bypass surgery is performed under general anaesthesia and typically takes between 2 and 4 hours. In most cases, the procedure is carried out using laparoscopic (keyhole) surgery, which involves making several small incisions (cuts) rather than one large cut.

The procedure involves the following:

1. Your surgeon will make several small cuts on your abdomen.
2. A thin tube with a small camera (a laparoscope) is inserted through one of the cuts, sending a magnified view of your insides to a screen. Long, slim surgical tools will go through the other cuts, allowing your surgeon to operate while watching the screen.
3. Your surgeon opens up the space behind the upper part of your stomach so they can safely divide it in the next step.
4. Using a stapling device, your surgeon separates the top of your stomach to create a small pouch. This pouch becomes your new, much smaller stomach, so you'll feel full after eating far less food. The rest of your original stomach stays in place, but no longer receives food.
5. The small bowel will be divided 100 to 200cm below where it normally joins your stomach. This creates two ends: one that will be joined to your new pouch, and one that carries digestive juices from the bypassed stomach and upper bowel.
6. The lower end of the bowel will then be attached to the new pouch. The food you eat will now travel from your mouth into the small pouch and directly into this lower section of bowel, skipping most of your stomach and the first part of your small intestine. This is what "bypass" means.
7. Finally, your surgeon reconnects the other end further down, so digestive juices can rejoin the food and continue breaking it down. Because food now spends less time in contact with the bowel, your body absorbs fewer calories and nutrients.

Clips, staples and implants used during surgery do not react with the body and can remain safely in place for life.

If keyhole surgery is not possible, the operation may be converted to open surgery.

How long does it take to recover from gastric bypass surgery?

In hospital

You’ll wake in the recovery area before moving to the ward. If you have other medical conditions, you may spend time in a high dependency unit.

You’ll start with a liquid-only diet, taking small sips to protect the new stomach pouch.

Most patients can go home the next day.

Diet progression

1. A liquid-only diet is administered for your first several weeks
2. After this timeframe, soft foods can be introduced
3. You’ll be able to consume solid foods after 4–6 weeks.

Your dietitian will guide you through each stage.

Vitamins and supplements

You will need lifelong vitamin and mineral supplements and regular blood tests, which will be done under the supervision of your GP. Your GP will be informed about you undergoing the surgery and the need for lifelong follow-up and care.

Activity

• Walking is advised from day one of your operation
• An exercise programme will be given to you after one week
• You’re able to go back to work around 2–4 weeks
• Avoid heavy lifting for several weeks
• You can drive once you can safely control your vehicle. Check with your insurer and surgeon before driving again
• You may need to delay flying – it’s best to check with your airline or national aviation authority about any restrictions.

Red flag symptoms

Contact your healthcare team immediately if you notice:

• Worsening or severe pain
• Fever or shivering
• Feeling faint or short of breath
• Persistent nausea or loss of appetite
• Not passing wind or opening your bowels

These may indicate a serious complication.

What are the risks and possible complications of gastric bypass surgery?

Gastric bypass surgery is generally safe, but all surgery carries risks. Your surgeon will discuss your individual risk profile.

General surgical risks

• Pain
• Bleeding
• Infection
• Scarring
• Hernia at the incision site
• Blood clots (DVT)

Keyhole surgery risks

• Hernia near one of the keyhole cuts
• Damage to the bowel, bladder or blood vessels
• Surgical emphysema (trapped gas under the skin)
• Gas embolism (very rare)
• Conversion to open surgery

Gastric bypass specific risks

• Pouch stenosis
• Staple line bleeding
• Anastomotic leak
• Internal hernia
• Change in bowel habit or diarrhoea
• Nutritional deficiencies (lifelong supplements needed)
• Anastomotic ulcer (higher risk if you smoke)
• Gallstones

Long-term expectations

A safe amount of weight to lose is around 0.5–1 kg per week for the first year, so you’re still maintaining muscle mass while losing body fat. Most patients lose 60–70% of their excess weight within 12–18 months.

How much does gastric bypass surgery cost at Nuffield Health?

For pricing information, please get in touch with your local hospital. The hospital or your healthcare team will provide you with a fixed, all-inclusive price for the treatment after your initial consultation.

Making the right decision

Choosing to have gastric bypass surgery is a personal decision. At Nuffield Health, you’ll never be rushed. Our surgeons will help you understand what’s achievable, what to expect and how to prepare, so you feel confident every step of the way.