Common FAQs

Your Body Mass Index (BMI) is the ratio of your weight (in kilograms) to the square of your height (in meters). For example, if you weigh 140 kg (22 stones) and your height is 1.75 meters, your BMI = 140 / (1.75 × 1.75) = 45.7 kg/m². You may be more comfortable to think about your weight in stones and pounds (1 stone = 6.35 kg), and your height in feet and inches (1 meter = 3 feet and 3 inches).

Use a BMI calculator

You can have healthy weight, overweight or obesity based on your BMI. Your BMI is healthy if it is 18.5–24.9 kg/m². If your BMI is 25–29.9 kg/m² you are overweight. You are obese if your BMI is more than 30. You have morbid obesity if your BMI is more than 40, or if your BMI is more than 35 and you have comorbidity. If your ethnic origin is Asian or African, the BMI limits are lowered because you are likely to have higher genetic risks than Caucasians.

Weight loss after bariatric surgery is talked about usually as ‘percentage excess weight lost’. You may see this written as %EWL. Your excess weight is the weight that is over and above your ideal weight. Your ideal weight is taken as the weight that would give you a BMI of 25. Your excess weight is calculated by subtracting your ideal weight from your actual weight.

For example, if you are 5 feet 6 inches tall and you weigh 19 stones, your BMI is 43. For your height, your ideal weight is about 11 stones (this would make your BMI 25). So, your excess weight is 19 − 11 = 8 stones. If you were to lose 4 stones, then you have lost 50% of your excess weight. If you lose 6 stones, then you have lost 75% of your excess weight, and so on.

Comorbidity means any medical condition that is caused by obesity. Common comorbidities are high blood pressure, diabetes, dyslipidemia (high cholesterol), heart disease, obstructive sleep apnea, asthma, fatty liver disease, acid reflux, joint problems, polycystic ovarian syndrome (PCOS), and depression. Also, obesity increases the risk and the aggressiveness of several types of cancer. Obesity shortens your life expectancy.

Bariatric surgery is the proper name for weight loss surgery. The word ‘bariatric’ is derived from the Greek word ‘bar’, which means weight. ‘Bariatric’ is the branch of medicine that deals with problems of overweight and obesity.

Diabetes, high blood pressure and lipid disorder (high cholesterol) are together called the metabolic syndrome. The metabolic syndrome increases your risk for heart attacks. Bariatric surgery is also called Metabolic Surgery because it can reduce the severity of the metabolic syndrome, or even cure this condition, and reduce your risk for heart disease.

Almost all medical conditions (called comorbidity) caused by obesity are improved or even cured by bariatric surgery. About 3 in 4 patients with diabetes get normal blood sugar levels and are able to stop taking anti-diabetes medicines. About 2 in 3 people with high blood pressure and disordered lipids (high cholesterol) will get normal blood pressure and lipid levels, and will not need to take drugs. For others, the conditions may not disappear but the severity may reduce and fewer medicines may be needed.

Also, substantial improvements may be seen in obstructive sleep apnea, polycystic ovarian syndrome (PCOS), asthma, joint pains, sexual dysfunction and quality of life. Some women with infertility are able to become pregnant. Several studies have shown that obese people who have bariatric surgery live significantly longer than obese people who do not have bariatric surgery.

All weight loss operations reduce the working size of the stomach. This is called the restrictive effect of bariatric surgery. But there is much more than restriction. With the gastric bypass and the gastric sleeve, there are changes in the levels of many hormones that control your hunger, fullness and blood sugar levels. These hormones are released from special cells in the lining of the small bowel and the stomach. Because of these changes in hormone levels, you can feel as if a switch has been turned off in your head. Your hunger is reduced and you feel full quickly after eating.

With the gastric band, the effect appears to be through the nerve endings in the wall of your stomach. When the band is properly inflated, stimulation of the nerve endings controls your appetite and gives fullness with small meals.

Q: Is bariatric surgery safe?

Performed in hospital with specialist teams; risks discussed in consent. For many, it’s safer than remaining with severe obesity.

Q: Will I still enjoy food?

Yes. With support, patients enjoy balanced meals and food freedom.

Q: How long is recovery?

Most return to light work in ~10–14 days; full recovery varies.

Q: Is it “the easy way out”?

No—surgery is a tool. Success needs lifestyle change and follow-up.

Q: What if I have reflux?

We investigate and tailor procedure choice (often RNY preferred).

Q: Can I finance surgery?

Ask our team about payment options and staged planning.

Q: I had surgery before and regained weight—can you help?

Yes. We assess causes and consider revision options.

It is a common worry that bariatric surgery may cause malnutrition because food will not get absorbed. In fact, there is little malabsorption of carbohydrate, protein or fats after a standard gastric bypass, gastric sleeve or gastric band (a truly malabsorptive operation is called bilio-pancreatic diversion with duodenal switch). But you can get malnutrition if you do not eat properly or if you do not follow-up with your doctor.

After bariatric surgery, it is vital that you follow the dietician’s advice, take the prescribed nutritional supplements and have regular tests.

Please bear in mind that bariatric surgery is not a cure for obesity. No weight loss operation is a magic wand, and it is not an easy way out of the problem. You will have to work hard to get the benefit out of the operation. Think of weight loss surgery as a powerful tool for weight loss. Like any tool, it will work only as well as you use it and maintain it.

You will have support from our specialist dietician to help you to change your eating habit. But, ultimately, the responsibility is yours. Apart from healthy eating, regular physical exercise is very important for losing weight and for maintaining weight. You should make the time and put in the effort to exercise properly. You may not achieve satisfactory weight loss if you do not put in the effort that is needed. In the longer term, you can regain lost weight if you do not continue to take care.

Lifelong follow-up is essential after weight loss surgery. You can contact us at any time for advice. You can think of the follow-up care in 3 parts:

Advice about diet and life-style

You will be given advice by Dilek. It is vital that you listen to the advice and discuss any problems or concerns. The dietician is a particularly important person. She will give you detailed instructions. Please keep in regular touch with the dietician. 

Nutritional Supplements

After gastric sleeve or gastric bypass, you should take a multi-vitamin and mineral preparation daily. We recommend multivitamin one capsule daily. You can take whole capsules or tablets.

A detailed discharge summary will be sent to your GP, explaining the medicines and follow-up tests. Please make an appointment to see your GP soon after your operation.

Tests

You will need to have blood tests regularly at your GP’s centre. After gastric sleeve and gastric bypass, the tests should be done 3-monthly during the first year, and then one-yearly. 

For more information about follow-up medicines and tests, see http://www.bomss.org.uk/bomss-nutritional-guidance/

You will need to take a special diet, called a liver reduction diet, for 2 weeks before your weight loss operation (length various patient to patient). The liver overhangs the stomach, and it is necessary to move the liver out of the way during weight loss surgery. The liver can get quite heavy in obese people.

The purpose of the liver reduction diet is to make the liver lighter and easier to handle, and so make the operation safer. The liver reduction diet is rich in proteins and low in carbohydrates and fats, and it will deplete a substance called glycogen that is stored in your liver. You will be given written instructions about the liver reduction diet.

You need to stay in hospital for 1–2 nights after the operation.

There is no restriction on activity after the operation. You can take light exercise, within the limits of your comfort. There is no hard and fast rule about returning to work or driving. It is mainly common sense, and you should do what you feel you are able to do.

Care of bone health is really important after bariatric surgery, particularly after gastric bypass. There is increased risk of fractures after bariatric surgery. Bones are living, dynamic organs in the human body and bone health is critically dependent on calcium, phosphorous, vitamin D and parathyroid hormone.

Unlike carbohydrates and fats, the human body does not store proteins; regular intake is essential. Normal protein requirement is 30–60 g/day. Bariatric surgery can sometimes cause intolerance to protein-rich foods, leading to insufficient intake. Regular assessment and counselling by a specialist dietician is very important. With proper dietary advice, protein malnutrition is rare. Prioritize protein; carbohydrates and fats are secondary.

Iron deficiency is a main cause of anaemia after bariatric surgery (another is vitamin B12 deficiency). Anaemia = low haemoglobin; common symptom is fatigue. Iron exists as heme (meat) and non-heme (plant) iron; non-heme is less well absorbed, so vegetarians need almost twice the dietary iron. Healthy adults absorb only 10–15% of dietary iron.

Vitamin C enhances absorption (take iron with a vitamin C-rich drink). Tannins (tea) and calcium reduce absorption and shouldn’t be taken with iron. RDA: men 8 mg/day; menstruating women 18 mg/day (8 mg after menopause). Poor-quality diets can be iron-deficient, and some patients are anaemic pre-op.

Iron absorption needs acid and occurs mainly in the duodenum/upper jejunum. About 50% of gastric bypass patients develop iron deficiency due to low gastric acid and bypassed duodenum; reproductive-age women are at highest risk. Ferritin reflects iron stores; low ferritin (< ~15 µg/L) implies deficiency.

Daily iron supplementation is recommended after bypass and sleeve. Multivitamins alone (e.g., 12 mg elemental iron in one Forceval®) are insufficient.

For iron-deficiency anaemia: 50–60 mg elemental iron twice daily for 3 months (e.g., 300 mg ferrous sulphate tablet ≈ 60 mg elemental iron). Split doses reduce absorption limits and side-effects (nausea, cramps, diarrhoea/constipation). Monitor reticulocyte count, ferritin and haemoglobin.

Use iron cautiously: overload can damage liver/heart, especially with haemochromatosis.

Vitamin B12 is necessary for red blood cell formation and nerve function. It’s naturally in animal products. In the stomach, acid and enzymes free B12 from proteins; it binds Intrinsic Factor (from lower stomach), and the complex is absorbed in the distal ileum.

After gastric bypass, low acid and diversion from the Intrinsic Factor-producing area predispose to B12 deficiency. With sleeve gastrectomy, B12 meets Intrinsic Factor, but reduced acid may still affect absorption.

B12 deficiency causes megaloblastic anaemia (fatigue) and neurological symptoms (numbness/tingling, balance issues, depression, confusion, poor memory). Levels < ~170–250 pg/ml indicate deficiency. RDA: 2.4 mcg. Start B12 supplements within 6 months post-op; intramuscular injections every 3 months are the most reliable.

Vitamin B1 (Thiamine) supports enzymes (e.g., transketolase) for carbohydrate metabolism and maintains nerve myelin. The body doesn’t store B1, so daily intake is required. A daily multivitamin after bariatric surgery is routinely prescribed and usually sufficient; routine thiamine testing isn’t necessary.

Mild deficiency: calf muscle pain after slight activity, tingling/numbness/weakness (peripheral neuropathy); treat with B-complex 2–3× daily. Severe deficiency can develop with prolonged vomiting post-op and can cause unstable gait, impaired consciousness and memory loss. Urgent hospitalization with IV thiamine (avoid glucose IVs) and correction of underlying issues is essential.

Obesity increases gallstone risk due to bile composition changes. Rapid weight loss after bariatric surgery further alters bile and can make silent stones symptomatic or form new stones. About 1 in 4 patients may need treatment for gallstones after weight loss surgery.

Dumping is a set of unpleasant symptoms after gastric bypass (and sometimes sleeve), especially with poor food choices. Sugary, fatty and fried foods trigger it. Early dumping (30–60 minutes after eating): sweating, flushing, palpitations, cramps, nausea, diarrhoea—due to rapid food entry into the small bowel and hormone release. It’s often mild and discourages unhealthy eating; it lessens over time. Avoid liquids with meals and increase starch, fibre and protein to minimize.

Late dumping (1–3 hours post-meal) is rarer and due to reactive hypoglycaemia (sweating, shakiness, poor concentration, fainting). A small amount of sugar about one hour after the meal usually helps.

Constipation can occur after any bariatric operation, usually from insufficient water and fibre. Calcium or iron supplements can contribute. Laxatives may occasionally be necessary.

As weight is lost, stretched skin may not regain tone, leading to loose folds—commonly in the lower abdomen, upper arms and thighs. For some, this causes minor discomfort; for others, it can cause embarrassment, hygiene issues or skin-fold infections. Plastic surgery may be required to deal with loose skin.

Q: I’m from the UK—what does aftercare look like?

Structured tele-follow-ups, UK-friendly pathways, and optional group support.