Obesity shortens life expectancy and is associated with a wide range of serious medical problems, ranging from diabetes and heart disease through to infertility and cancer. Losing weight can significantly improve or cure these conditions and, in the long-term, reduce the chances of future health problems developing. Mr David Kerrigan is a weight-loss surgery consultant based at Spire Murrayfield Hospital in Wirral, one of several Gravitas clinics (www.gravitas-ltd.co.uk) in the UK.

Q What type of person do you think benefits most from weight-loss surgery?
A You would be considered suitable for bariatric surgery if you have a body mass index (BMI) of over 40, as this level of obesity is associated with a risk of serious health problems. If you suffer with medical problems that might improve with weight loss, such as diabetes or high blood pressure, the minimum cut-off for surgery is lowered to a BMI of 35. 

Q What are the different types of bariatric surgery?
A Gastric banding: a soft, adjustable collar (the band) is clipped around the top of the stomach. When inflated, the band will grip and squeeze gently on the stomach wall. This pressure delays the passage of solid food through the upper part of the stomach, creating a sensation
of fullness, even with small portions.

Gastric bypass: controls portion size, by creating a small pouch of stomach at the bottom of the gullet. This is completely separate from the rest of the stomach. Swallowed food can't enter the stomach any more and is redirected into the intestine. This stops patients from absorbing some of the calories they've consumed, because food is kept away from the stomach's digestive juices.

Duodenal switch (DS): Surgically separates food from the digestive juices. A shorter length of bowel is left with which to absorb food. This means they can lose weight without drastically reducing portion size. All three types of bariatric surgery can be performed with keyhole (laparoscopic) surgery.

Q How will my eating habits change following bariatric surgery?
A Gastric banding: chew food carefully and eat slowly, but you can eat most foods in small amounts.
Gastric bypass: eat slowly, chew food carefully and stick to small portions but sugary foods can cause 'dumping syndrome' (fainting, cramps and diarrhoea).
Duodenal switch: eat normal-size meals after about a year, but you have to stick to a high- protein diet and take vitamin and mineral supplements.

Q How can having a  weight-loss operation change people's lives?
A For people with Type 2 diabetes, with gastric bypass and duodenal switch operations around 70-90% of patients can expect to come off all treatment. Weight loss also improves numerous medical conditions, including angina, high blood pressure, high cholesterol, asthma, sleep apnoea, painful joints, weight-related depression, polycystic ovaries and infertility.

Q What risks are associated with weight-loss surgery?
A Gastric banding: initial risk is minimal (there is a low mortality rate of about one in 2,000). But after five years, at least one in 10 gastric band patients will have to undergo further surgery to fix a band problem. 

Gastric bypass: involves cutting and rejoining sections of the bowel, if the joins don't heal properly, food and gastric juices can leak out in the first three or four days. This can lead to peritonitis.This occurs in 2-3% of cases.
Duodenal switch: shares many of the same risks of a gastric bypass and it can also lead to nutritional problems unless care
is taken to stick to a high-protein diet, and to take vitamin supplements. Too much fatty food can lead  to loose, foul-smelling stools.