Frequently Asked Questions about Gastric Bypass

How much weight will I lose with a gastric bypass?

The national average weight loss following a gastric bypass is 60-70% of excess body weight over a 12-18 month period. Weight loss is generally quite fast initially but will settle into a regular pattern.

Will I lose weight quickly?

Weight loss commences when the liver reducing diet is introduced prior to surgery. Post operative weight loss can be quite rapid in the first six to eight weeks but then will settle into a steady monthly reduction until around 18 months. Long term success is related directly to a patient's motivation and their commitment to following the dietary guidelines provided.

How long will I have to stay in hospital after surgery?

You will normally stay in hospital for two nights for this type of procedure. The first night you will be in our High Dependency Unit.

Will I have to take medication after surgery?

Yes. All gastric bypass patients will need to take nutritional supplements and medication to protect the stomach. Calcium, multivitamins, iron, B12, folic acid and a protein pump inhibitor will be prescribed by your GP to commence two weeks after your operation. These medications will be discussed during your consultation and pre-assessment prior to surgery.

How will my diet change after surgery?

It is vital that only liquids are consumed for the first two weeks to reduce the risk to the stitches and healing in the stomach. Then there is a need to restrict the consistency and type of foods that can be consumed in order to progress the healing and because of the presence of swelling between the opening of the new stomach pouch and the intestine. The new stomach pouch is much smaller and subsequently has a smaller capacity to store anything that you eat. This means you won't be able to eat large volumes of food. You will feel full very quickly (after only a few teaspoons initially) and your appetite should decrease. As the body adjusts and swelling settles there will be some give allowing for more solid food to be consumed.

You will not be able to eat the same volume of food as you do now. By the end of the first year you should be able to eat a child sized portion of food. This will gradually increase as your weight stabilizes and your tolerance increases.

Due to dietary restrictions, it is important to protect against nutritional deficiencies. Following surgery you should have a multivitamin, calcium and iron supplement which will protect against the risk of osteoporosis and anaemia. Occasionally a zinc deficiency may occur and you may be prescribed a further supplement. An anti-acid tablet will help to reduce stomach acid and prevent the formation of ulcers. Immediately following surgery, the body is healing, so it is important that you still consume adequate calories and protein to promote recovery.

What if I am still hungry after surgery?

Most patients experience a reduction in hunger following a gastric bypass though some patients continue to feel hungry at times. It is important to make lifestyle changes and change eating habits to best manage those symptoms. 'Head hunger' and 'stomach hunger' can be different and it is important to learn to recognise the difference at the early stages. Habit and food dependence may need to be addressed to reduce those symptoms.

What are they potential problems after surgery?

Although unlikely, the stomach could "leak" where it has been stitched. This would be evident within the first 24 hours after surgery and is the reason patients stay in the High Dependency Unit for the first night so they can be continually monitored. You may experience "dumping syndrome" if you eat the wrong type of foods after bypass surgery. The food goes straight into the small intestine and if you eat something sweet and high in calories the body may react to having this type of food "dumped" directly there. A patient may feel shivery, sweaty, tired and unwell. Symptoms last an hour or two and is a side effect which gives the patients the incentive to make sensible food choices.

Following successful weight loss surgery, some people experience thinning of the hair. This is a temporary side effect, normally occurring between three and six months after surgery. The hair does thicken up again.

You will require regular blood tests to ensure your supplements are adequate and you do not become anaemic as food is no longer fully absorbed.

Can the surgery be reversed?

No. It is vital that a lifetime commitment is made by the patient prior to proceeding to surgery.

Find a treatment, test or scan available at:


Find a consultant

Use one or more of the options below to search for a consultant and link through to view their Spire profile.


Let us help you

fill out this form and we will get back to you:

Please select a hospital

We can call you

Please enter your details below and we will call you back.

What is the aim of your enquiry?

Please select a hospital

If we are unable to reach you by phone, please include your email address so that we can get in touch...

Calculate my BMI

1. Enter your height



2. Enter your weight



© Spire Healthcare Group plc (2016)