Obesity and Its Surgical Treatment

Obesity is a chronic disease in which fat accumulates in the body to a degree that harms health, and which requires long-term follow-up. It is not simply a matter of appearance or willpower.

Obesity can develop through the combined effect of genetic predisposition, appetite and satiety mechanisms, hormones, medicines being taken, sleep, stress, the food environment, physical activity and social circumstances. For this reason, treatment should take an individualised and sustainable approach rather than one that blames the patient.

The treatment of obesity does not aim solely to reduce the number on the scales. The real aim is:

• To bring conditions such as diabetes, high blood pressure and sleep apnoea under control
• To improve mobility and quality of life
• To reduce the risk of cardiovascular disease
• To help keep the lost weight off in the long term
• To build healthier and sustainable lifestyle habits.

Treatment may involve considering dietary changes, physical activity, support for behaviour change, medicines and, in suitable patients, metabolic and bariatric surgery together. Surgery is not a sign that other treatments have failed; it is one of the evidence-based options in the treatment of obesity [1–3].

Why does obesity develop?

Taking in more energy than is used is an important factor in weight gain; however, this alone does not explain everything.

Factors that may contribute to the development of obesity include:

• Genetic and family predisposition
• Differences in the mechanisms that regulate appetite and satiety
• Easy access to calorie-dense and processed foods
• Reduced physical activity
• Irregular sleep and sleep apnoea
• Stress, depression and certain eating behaviour problems
• Certain hormonal disorders
• Cortisone, certain psychiatric medicines and certain diabetes medicines
• Stages of life such as pregnancy and the menopause
• Changes in appetite after stopping smoking
• Working conditions and social environment

An underactive thyroid gland can contribute to weight gain; however, it is neither the only nor the most common cause of obesity. Whether there is an underlying hormonal disorder is determined by a doctor’s assessment.

Which health problems is obesity associated with?

Over time, obesity can increase the risk of developing the following conditions:

• Type 2 diabetes
• High blood pressure
• Raised cholesterol and triglycerides
• Cardiovascular diseases
• Sleep apnoea
• Fatty liver and fatty-liver-related inflammation of the liver
• Heartburn and reflux
• Knee, hip and back pain
• Polycystic ovary syndrome and fertility problems
• Urinary incontinence
• Depression and reduced quality of life
• Certain types of cancer

Not every person with obesity develops all of these conditions. The risk varies according to how fat is distributed in the body, age, genetic characteristics and coexisting conditions.

How is the body mass index calculated?

The most commonly used measure in assessing obesity is the body mass index (BMI).

BMI = Body weight (kg) ÷ Height squared (m²)

The general classification in adults is as follows:

• BMI 18.5–24.9: Range considered healthy
• BMI 25–29.9: Overweight
• BMI 30–34.9: Class 1 obesity
• BMI 35–39.9: Class 2 obesity
• BMI 40 and above: Class 3 or severe obesity

BMI is a useful screening measure; however, it does not directly show the amount and distribution of fat in the body. On its own it can be misleading in people with high muscle mass or in older age. For this reason, treatment decisions are not made on the basis of BMI alone.

What else is looked at during the assessment?

The following are taken into account when assessing the patient:

• Waist circumference and body fat distribution
• The course of weight gain and previous treatments
• Eating and physical activity habits
• Medicines being taken
• Blood sugar and HbA1c
• Cholesterol and triglyceride levels
• Liver and kidney function
• Thyroid tests
• Nutrients such as iron, vitamin B12, folate and vitamin D
• Symptoms of sleep apnoea
• Heart and lung health
• Reflux and stomach complaints
• Psychological state and eating behaviours

Where necessary, a sleep study, a cardiology assessment, an abdominal ultrasound scan or an upper gastrointestinal endoscopy may be carried out. The need for endoscopy is determined by factors such as reflux, stomach pain, difficulty swallowing, anaemia and the type of operation planned.

Obesity treatment is planned individually. It is not right to apply the same diet, the same medicine or the same operation to every patient.

When the treatment plan is drawn up,

• BMI
• Obesity-related conditions
• Previous treatments
• Eating behaviour
• Daily life and working conditions
• Medicines being taken
• The patient’s preferences and adherence to treatment

are all assessed together.

Diet and lifestyle treatment

The foundation of treatment is sustainable eating habits, regular physical activity, adequate sleep and behaviour change.

The aim is not to lose as much weight as possible in a very short time, but to establish a routine that suits one’s state of health and can be maintained for a long time.

With the support of a dietitian,

• Adjusting portion sizes
• Eating enough protein and fibre
• Reducing sugary drinks and high-calorie processed foods
• Recognising emotional eating and uncontrolled snacking
• Planning a meal pattern suited to the individual

can all be achieved.

Physical activity should initially be suited to the person’s joint, heart and breathing condition. The amount of activity should be increased gradually.

Losing even about 5–10 per cent of body weight can bring meaningful improvements in blood sugar, blood pressure, fatty liver and exercise capacity [2,3].

Who are obesity medicines suitable for?

In suitable patients who have not achieved adequate results with lifestyle changes, obesity medicines can be used under medical supervision.

Today there are various options, including GLP-1 or GIP/GLP-1-based medicines that reduce appetite, increase the feeling of fullness and help regulate blood sugar. In some patients these medicines can lead to marked weight loss.

However:

• Not every medicine is suitable for every patient.
• Side effects such as nausea, vomiting, diarrhoea, constipation and gallbladder problems may occur.
• The choice of medicine should take into account coexisting conditions and other medicines being taken.
• They should not be used during pregnancy.
• Weight may be regained when treatment is stopped.
• They should not be obtained from the internet or from anyone other than a doctor.

The current approach of the World Health Organization recommends that these medicines be considered not as a short-term slimming measure but as part of long-term obesity treatment, together with nutritional, physical activity and behavioural support [2].

Obesity surgery is also referred to as “metabolic and bariatric surgery”. This is because these operations do not only lead to weight loss; they can also have beneficial effects on blood sugar, blood pressure, sleep apnoea and other metabolic problems.

Current scientific evidence shows that metabolic and bariatric surgery is one of the treatment options that is effective and gives long-lasting results in severe obesity [1].

Who is surgery an option for?

According to the 2022 ASMBS/IFSO guideline, metabolic and bariatric surgery:

• may be recommended in people with a BMI of 35 or above, regardless of whether they have an obesity-related condition.
• may be considered in people with a BMI between 30 and 34.9, particularly if there is a metabolic disease such as type 2 diabetes, or if adequate and lasting weight loss or disease control has not been achieved with non-surgical methods [1].

These are current international guideline criteria. Countries’ health systems, reimbursement rules and hospitals’ practice conditions may differ.

BMI alone is not enough to decide on an operation. When the decision is made,

• The patient’s general state of health
• Coexisting conditions
• Presence of reflux
• Previous operations
• Eating habits
• Smoking and alcohol use
• Plans for pregnancy
• Ability to attend regular check-ups
• The benefit the operation will bring and its possible risks

are all assessed together.

Older age on its own is not an absolute barrier. General health, frailty, organ function and the expected benefit of the operation matter more than age.

Who is obesity surgery an option for in Türkiye?

The 2026 Clinical Protocol for Obesity and Metabolic Surgery of the Ministry of Health of the Republic of Türkiye recommends that the decision to operate should take into account not only the body mass index but also the effects of obesity on the person’s health [7].

According to the protocol, in adults who have not achieved adequate weight control with diet, physical activity, behaviour change and appropriate medical treatments applied for a sufficient period, metabolic and bariatric surgery may be considered in the following situations:

• BMI of 40 kg/m² or above: Surgical treatment may be carried out even if there is no obesity-related condition.
• BMI between 35 and 39.9 kg/m²: Surgical treatment may be carried out in people with a significant obesity-related health problem such as type 2 diabetes, high blood pressure, sleep apnoea, fatty liver or restricted mobility.
• BMI between 30 and 34.9 kg/m²: Surgery may be considered in patients with type 2 diabetes whose blood sugar cannot be adequately controlled with other treatments, or in selected people with serious obesity-related organ damage and significant health problems.
• BMI below 30 kg/m²: According to the Ministry of Health protocol, metabolic and bariatric surgery is not performed [7].

What is the Edmonton Obesity Staging System?

The Edmonton Obesity Staging System assesses not only a person’s weight but also the extent to which obesity affects their health and daily life.

In simplified form:

• Stage 0: There are no significant obesity-related risk factors, diseases or limitations in daily life.
• Stage 1: There are mild changes in blood sugar, blood pressure or liver values, or mild complaints in daily life.
• Stage 2: There is a significant obesity-related disease such as type 2 diabetes, high blood pressure, sleep apnoea, fatty liver or joint problems.
• Stage 3: There is obesity-related organ damage, significant restriction of mobility or health problems that markedly affect daily life.
• Stage 4: There are advanced or end-stage complications of obesity-related diseases.

This system shows that two people with the same BMI may differ in their state of health and in the benefit they would gain from an operation.

Are there differences between the international guidelines and the Turkish Ministry of Health guideline?

The 2022 ASMBS/IFSO international guideline recommends metabolic and bariatric surgery in people with a BMI of 35 kg/m² or above, even if they have no coexisting condition. For a BMI between 30 and 34.9 kg/m², it supports considering an operation in people who have a metabolic disease or who have not achieved adequate and lasting results with non-surgical methods [1].

The 2026 protocol of the Turkish Ministry of Health, on the other hand, takes into account the severity of obesity-related diseases together with Edmonton staging, particularly in the BMI range of 35–39.9 kg/m² [7].

These criteria do not mean that the decision to operate is made automatically. The decision to operate should be made by a multidisciplinary team, taking together into account the patient’s general state of health, eating habits and behaviours, psychological state, anaesthetic risk, previous treatments and ability to keep to lifelong follow-up.

How is the pre-operative assessment carried out?

Before the operation, the patient’s entire state of health is assessed, not only their weight.

Depending on the patient’s needs,

• Metabolic and bariatric surgeon
• Specialist in endocrinology or internal medicine
• Dietitian
• Anaesthetist
• Psychiatrist or psychologist
• Specialist in respiratory and sleep medicine
• Cardiologist

may be part of the assessment team.

The psychological assessment is not carried out to exclude the patient from surgery; it is carried out to identify and provide support for uncontrolled eating behaviour, depression, addiction or problems that may affect adherence after the operation.

Smoking can impair wound healing and increase the risk of ulcers and lung complications in particular. For this reason, it is important to stop before the operation.

Which operations are performed?

Sleeve gastrectomy (tube stomach operation)

About 75–80 per cent of the stomach is removed, leaving behind a narrow, tube-shaped stomach. This reduces the volume of the stomach and changes the hormones associated with hunger and fullness.

Main features:

• It is currently one of the most commonly performed procedures.
• The route of the intestines is not changed.
• It can lead to weight loss and marked improvement in metabolic diseases.
• It is an irreversible procedure.
• In some patients, new reflux may develop or existing reflux may worsen.
• Regular follow-up is required because vitamin and mineral deficiencies may occur.

In patients with significant reflux or reflux-related damage to the oesophagus, a sleeve gastrectomy may not always be the most suitable option [1,6].

Roux-en-Y gastric bypass

A small stomach pouch is created in the upper part of the stomach and a new connection is made with the small intestine, shortening the path along which food travels, is digested and is absorbed in the small intestine. As a result, both the amount of food that can be eaten is reduced and there are changes in gut hormones and in the absorption of nutrients.

Main features:

• It can have a strong effect on weight loss and type 2 diabetes.
• In some people with reflux disease it may be more suitable than a sleeve gastrectomy.
• Deficiencies of iron, vitamin B12, calcium and other vitamins and minerals may be more pronounced.
• Procedure-specific problems such as ulcers, bowel obstruction, internal hernia and dumping syndrome may develop.
• It requires regular, lifelong follow-up.

Other surgical and procedural options

Although sleeve gastrectomy and Roux-en-Y gastric bypass are the most commonly performed operations, other surgical or endoscopic methods may be considered in some patients.

None of these methods is the best option for everyone. The decision should be made by considering together the body mass index, type 2 diabetes, reflux, previous operations, eating habits and the ability to keep to lifelong follow-up [1,7].

One-anastomosis gastric bypass

In this operation a small, long stomach pouch is created and a single connection is made with the small intestine. As a result, both the amount of food that can be eaten is reduced and the path food takes through the intestine is shortened.

It can be effective for weight loss and for controlling type 2 diabetes. However, procedure-specific problems such as bile reflux, anaemia and vitamin, mineral and protein deficiencies may develop. For this reason, appropriate patient selection, regular blood tests and lifelong nutritional follow-up are important [1,7].

SADI-S and duodenal switch

In these methods, in addition to a sleeve gastrectomy, the small intestine is rearranged in a way that changes the absorption of nutrients.

They may be considered particularly in selected patients with a very high body mass index, significant metabolic diseases, or a need for greater weight loss.

Their effects on weight loss and type 2 diabetes can be strong. However, the risk of protein, iron, calcium and vitamin deficiency is higher than with some other methods. After these operations it is essential to follow the recommended nutrition programme, take vitamin and mineral supplements and attend lifelong check-ups [1,6].

Adjustable gastric band

An adjustable band is placed around the upper part of the stomach to limit the amount of food that can be eaten. No part of the stomach or intestines is removed.

However, in the long term, insufficient weight loss, slipping of the band, erosion of the band into the stomach or the need for further surgery may occur. For these reasons, the use of the gastric band has declined today [6].

What is revision surgery?

In some patients who have previously had obesity surgery, over time

• Insufficient weight loss
• Regaining a substantial part of the weight lost
• Reflux that does not respond to treatment
• Persistent vomiting or difficulty eating
• Narrowing, ulcer or another surgical problem
• Serious vitamin, mineral or protein deficiency

may develop.

In these situations the cause of the problem is investigated first. Eating habits, medicines being taken, psychological factors and the stomach and intestinal anatomy created by the operation are assessed together. Not every case of weight regain requires another operation; treatment can also be provided with nutritional support, behavioural therapy or obesity medicines.

If considered necessary, correction of the previous operation or conversion to another method may be planned. For example, in selected patients who develop severe reflux that cannot be controlled after a sleeve gastrectomy, conversion to a gastric bypass may be considered.

Revision operations can be more complex than the first operation. For this reason, they should be carried out by experienced teams after detailed investigation and an assessment of benefits and risks [1,7].

Are endoscopic methods operations?

The gastric balloon and endoscopic sleeve gastroplasty are methods performed with an endoscope passed through the mouth, without any incision in the abdomen. They are not the same as surgical operations.

Gastric balloon

A balloon placed in the stomach by endoscopy and removed after a certain period creates a feeling of fullness in the stomach and can help the person eat less. The balloon is a temporary method; if nutritional and lifestyle support is not continued after it is removed, weight may be regained.

Endoscopic sleeve gastroplasty

The stomach is made smaller by placing stitches from the inside with the help of an endoscope. No incision is made in the abdomen and no part of the stomach is removed. It may be considered in selected patients who are not suitable for surgery or who do not wish to have surgery.

According to the 2026 protocol of the Ministry of Health of the Republic of Türkiye, endoscopic methods may be considered, in addition to lifestyle treatment, in selected people who have not achieved adequate results with previous diet and exercise efforts and who have a BMI of 30 kg/m² or above, or a BMI between 27 and 29.9 kg/m² with an obesity-related condition [7].

The weight loss achieved with endoscopic methods is generally more limited than with metabolic and bariatric surgery. Diet, physical activity and regular follow-up are needed to maintain the result.

Important information: The most suitable method is not the one that leads to the most weight loss, but the one that best suits the patient’s health problems, expectations and long-term safety. Which operation is “the best” varies from person to person. Reflux, diabetes, BMI, eating behaviour, previous operations and the ability to keep to lifelong follow-up are considered together when choosing the method. The decision on an operation or endoscopic procedure should be made together with the patient after a multidisciplinary assessment.

What are the benefits of obesity surgery?

In suitable patients, surgery:

• Can lead to marked and long-lasting weight loss.
• Can improve the control of type 2 diabetes and, in some patients, reduce the need for medicines.
• Can improve high blood pressure and blood lipids.
• Can reduce sleep apnoea.
• Can lead to improvement in fatty liver.
• Can help reduce joint pain and restricted mobility.
• Can improve quality of life.
• Can reduce the long-term health risks associated with severe obesity [1].

These benefits do not occur to the same degree in every patient. Guaranteed results such as “the diabetes will definitely go away” or “the weight will never come back” should not be expected.

What are the risks of the operation?

As with any surgical procedure, metabolic and bariatric surgery has risks.

Problems that may occur in the early period:

• Bleeding
• Infection
• Leakage at the stomach or intestinal connection
• Blood clots in the leg veins and clots travelling to the lungs
• Nausea, vomiting and fluid loss
• Lung problems
• Anaesthesia-related complications

Problems that may occur in the long term:

• Vitamin, mineral or protein deficiency
• Anaemia
• Reflux
• Gallstones
• Ulcer
• Narrowing (stricture)
• Bowel obstruction or internal hernia
• Excessive or insufficient weight loss
• Regaining part of the weight lost
• Need for further surgery

The risks vary according to the patient’s general condition, the method chosen, the experience of the surgical team and adherence to post-operative follow-up. The decision to operate should be made by weighing the expected benefits against the possible risks.

Related operationSleeve Gastrectomy →Read how the operation is performed and what recovery involves →

Related operationGastric Bypass →Read how the operation is performed and what recovery involves →

How long is the hospital stay after the operation?

The operations are mostly performed laparoscopically, that is, as keyhole surgery through small incisions. In patients without complications, the hospital stay is usually 1–3 days.

Current enhanced recovery protocols address effective pain control, prevention of blood clots, early mobilisation and starting oral fluids at the appropriate time together [4].

The length of the hospital stay may vary according to the type of operation, coexisting conditions and individual recovery.

How is eating resumed?

After the operation, eating is progressed gradually. Although the programme may differ between centres, it usually consists of

1. Clear or liquid diet
2. Protein-rich full liquids
3. Purée or soft foods
4. Well-chewed solid foods
5. Long-term balanced diet

as successive stages.

The transition usually takes a few weeks. Eating too quickly, not chewing well or drinking too much fluid with meals can cause pain, nausea and vomiting.

Protein and fluid targets should be set individually by a dietitian.

When can I return to work and daily life?

Most patients with desk jobs can return to work within about 2–3 weeks. For those doing heavy physical work, this period may extend to 4–6 weeks.

Starting light walking early is recommended. For heavy lifting and strenuous exercise, the surgeon’s approval should be awaited.

Why is lifelong follow-up necessary?

Although metabolic and bariatric surgery is a one-off operation, obesity is a chronic disease that requires lifelong monitoring.

During follow-up,

• Weight loss and possible weight regain
• Eating pattern
• Blood sugar and blood pressure
• Iron, vitamin B12, folate and vitamin D
• Calcium and bone health
• Liver and kidney function
• Psychological state
• Reflux and other digestive complaints

are assessed.

Vitamin and mineral deficiencies can also develop after a sleeve gastrectomy. This risk is more pronounced after gastric bypass and procedures that affect absorption to a greater extent.

Current guidelines recommend regular blood tests and lifelong continuation of vitamin and mineral supplements appropriate to the type of operation [5].

Vitamin supplements should not be stopped without a doctor’s advice, nor taken at random in high doses.

1. Eisenberg D, Shikora SA, Aarts E, et al. 2022 American Society for Metabolic and Bariatric Surgery and International Federation for the Surgery of Obesity and Metabolic Disorders: Indications for Metabolic and Bariatric Surgery. Surgery for Obesity and Related Diseases. 2022;18(12):1345–1356. https://pubmed.ncbi.nlm.nih.gov/36336720/
2. World Health Organization. WHO Guideline on the Use of GLP-1 Therapies in the Treatment of Obesity in Adults.2025. https://www.who.int/news/item/01-12-2025-who-issues-global-guideline-on-the-use-of-glp-1-medicines-in-treating-obesity
3. American Diabetes Association Professional Practice Committee. Obesity and Weight Management for the Prevention and Treatment of Diabetes: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1). https://diabetesjournals.org/care/article/49/Supplement_1/S166/163915/
4. Stenberg E, dos Reis Falcão LF, O’Kane M, et al. Guidelines for Perioperative Care in Bariatric Surgery: Enhanced Recovery After Surgery (ERAS) Society Recommendations: A 2021 Update. World Journal of Surgery.2022;46:729–751. https://pubmed.ncbi.nlm.nih.gov/34984504/
5. O’Kane M, Parretti HM, Pinkney J, et al. British Obesity and Metabolic Surgery Society Guidelines on Perioperative and Postoperative Biochemical Monitoring and Micronutrient Replacement for Patients Undergoing Bariatric Surgery—2020 Update. Obesity Reviews. 2020;21(11):e13087. https://pubmed.ncbi.nlm.nih.gov/32743907/
6. American Society for Metabolic and Bariatric Surgery. Bariatric Surgery Procedures: Sleeve Gastrectomy and Roux-en-Y Gastric Bypass. https://asmbs.org/patients/bariatric-surgery-procedures/
7. T.C. Sağlık Bakanlığı, Sağlık Hizmetleri Genel Müdürlüğü (Ministry of Health of the Republic of Türkiye, General Directorate of Health Services). Obezite ve Metabolik Cerrahi Klinik Protokolü (Obesity and Metabolic Surgery Clinical Protocol). Updated version, 2026. https://shgm.saglik.gov.tr/TR-117695/obezite-ve-metabolik-cerrahi-klinik-protokolu-2026-guncellendi-ve-yayimlandi.html