dr daniel mafi

Weight Loss Surgery Tauranga

weight loss surgery

What is obesity?

Obesity is a chronic, relapsing, debilitating, life-long disease, recognised by the World Health Organisation as a global pandemic.”  

In 2016 more than 1.9 billion people worldwide were overweight or obese. In New Zealand 32% of the adult population are obese. Being obese carries an increased risk of diseases (such as Diabetes) and death compared to normal weight individuals.   

Obesity tends to be defined by Body Mass Index(BMI) – a calculation that takes into account your weight (mass) and your height. Click here for our calculator.

body mass index
Risk of developing obesity-related disease*
Normal weight
18.5 - 24.9
18.5 - 24.9
30.0 – 34.9
35.0 – 39.9
Very high
> 40.0
Extremely high
*This includes: Type 2 Diabetes, high blood pressure,and heart disease

weight loss surgery

How is obesity treated?

Obesity results from too many calories consumed compared to calories burned. Treating this therefore simply involves either reducing calories in (dieting) or increasing energy expenditure (exercise) or both. Simple! Except, of course, that this is far from simple. Dieting and exercise (lifestyle changes) have long been the traditional methods of thinking about weight-loss – and very occasionally these efforts are successful.

However, for people who are morbidly obese (BMI > 40) this rarely produces sustained long-term results. Research shows that people using lifestyle changes alone may lose up to 10% of their body weight initially but most will regain two-thirds of that within the first 12 months of losing it, and all of it by 5 years.  In contrast, surgery for obesity alters the gastrointestinal system (the stomach and intestines) directly so as to reduce calorie intake into the body.

Click here to how weight loss surgery works?  This results in significant weight loss(typically of 60 – 70% of excess weight) sustained for the long term.

weight loss surgery

Is weight loss surgery right for you?

The decision of whether weight loss surgery is right for you (and if so, which surgery!) can be a difficult one. This decision is a joint one that can be made during your weight loss surgery consultation in Tauranga.

However, the Australian and New Zealand Metabolic and Obesity Surgical Society (ANZMOSS) offer the following criteria as guidelines for adults who may be suitable for weight loss surgery:  

  • Weight greater than 45kg above the ideal body weight for sex, and height.
  • BMI > 40 by itself or >35 if there is an associated obesity illness, such as diabetes or sleep apnoea
  • Reasonable attempts at other weight loss techniques
  • Obesity related health problems
  • No psychiatric or drug dependency problems
  • A capacity to understand the risks and commitment associated with the surgery

Weight loss SURGERY

How does weight loss surgery work?

1. Restriction

By reducing the capacity of the stomach to hold food (resulting in patients feeling full very quickly ie. early satiety)

2. Malabsorpation

By reducing the intestines ability to absorb calories 

Sleeve Gastrectomy

Weight loss SURGERY

What are my options for weight loss surgery?

Sleeve Gastrectomy

This operation, also known as Gastric Sleeve Surgery, is performed in Tauranga, involves reducing the size of the stomach by about 85% from a sac to a narrow tube. It is performed laparoscopically (keyhole surgery). It is the most common weight-loss operation currently performed in New Zealand.

The stomach usually functions as a reservoir that holds food and releases into the intestines in a controlled fashion. It allows us to eat big meals (eg 3 main meals / day).  Its usually capacity is about 1000mls.

Following gastric sleeve surgery, the stomach’s capacity is reduced to about 150mls. This means that a person will “feel full” very quickly, after only very small amounts of food.  In other words, a sleeve gastrectomy works mainly by a Restrictive mechanism. It also causes a reduction in some appetite-inducing hormones, and improves the way in which the body handles glucose and fats (less insulin-resistance).

Gastric Bypass

Gastric Bypass

Gastric Bypass has often been considered the “gold standard” for weight-loss surgery. It is a technically demanding operation that involves re-arranging the anatomy of the stomach and small intestines so that food “bypasses” (never comes into contact with – ) a significant portion of the small bowel.  Gastric bypass surgery results in less food (nutrients) being absorbed into the body – effectively and drastically reducing the number of calories consumed.

Re-arranging the anatomy involves:

(1)  The stomach being converted into only a very small pouch (50mls) by disconnecting the rest of the stomach

(2)  The small bowel is then divided and reconnected to both the stomach and to itself further downstream in a “Y” configuration.  This creates a segment of small bowel (usually 100 – 150cm in length), into which the food will flow first, that will have little-to-no absorptive function. The new route that the food takes “bypasses” the stomach and the area where important enzymes are usually added – enzymes that enable absorption of things like sugars and fats.  Effectively, this means that very few calories will be absorbed in the first 100 – 150cm of small bowel that the food travels down.

(3)  This initial segment is then rejoined to the usual (normal) circulation – where food will once again mix with those enzymes necessary for absorption. However, this “normal” segment that food travels down next is, now, much shorter.  This allows the body to absorb some nutrients (enough to live on) but not too many – thereby ensuring weight loss.  

The first part of the gastric bypass operation (the creation of the small stomach pouch) causes weight loss by restriction –limiting the amount of food that can be consumed and causing early satiety 

The second part of the operation (the bypass) causes weight loss by malabsorption. The body has less time (less length of small bowel) to absorb calories.

BMI Calculator

BMI stands for Body Mass Index and is an objective way of measuring body fat taking into account both weight and height. Different categories of BMI have been associated with varying health risks. Indeed a BMI below 18.5 or above 30 has been clearly associated with an increased risk of death (all-cause mortality). To calculate your BMI adjust each slider to the appropriate point and your BMI will be displayed.

0 - 15: Very severely underweight
15 - 16: Severely underweight
16 - 18.5: Underweight
18.5 - 25: Normal Range (healthy)
25 - 30: Overweight
30 - 35: Obese class I - Moderately obese
35 - 40: Obese class II - Severely obese
40: Obese class III: Very severely obese

weight loss surgery

What results can I expect after weight loss surgery?

A Sleeve Gastrectomy typically results in weight-loss of 60 – 70% of excess body weight, while a Gastric Bypass achieves 65 – 75%.  The majority of this weight loss occurs in the first 12 months after surgery – although weight can continue to fall for up to two years. Weight is usually fairly stable by 18 months.  

Occasionally a minor degree of weight regain can occur over time.  While the figures noted above are the expected and typical results, it is important to note that no specific degree of weight-loss is guaranteed. All weight loss surgery should be seen as a tool that enables the successful introduction of healthy lifestyle changes (diet and regular exercise) that will improve the long-term positive results achieved by the surgery.  Bay Surgery's weight loss surgery in Tauranga provides wrap-around care with pre- and postoperative consultations with a dietician and psychologist that help facilitate these changes.  Apart from weight loss both Sleeve Gastrectomy and Gastric Bypass surgery greatly improve (and sometimes “cure”) many of the obesity-related health problems, including Type 2 Diabetes, high blood pressure, and obstructive sleep apnoea. Joint pain from arthritis is also often greatly improved.

Potential complications of surgery

No surgery is risk free. Both Gastric Sleeve and Gastric Bypass are major operations that require a general anaesthetic and at least two nights in hospital. Though uncommon, these risks are real and must be seriously considered and understood prior to consenting to surgery.  The procedure and its risks will be thoroughly discussed with you during your consultations but please ensure that you clarify with Dr Mafi any aspect that you are unclear about prior to embarking on the surgical journey.

The risks of Obesity Surgery are:

General risks of any abdominal surgery

Bleeding: There is a 1 – 4% risk of bleeding during or immediately after surgery, to the extent that a blood transfusion is required.

Infection: All surgery carries risk of infection, ranging from minor infection of wounds to serious infections within the abdomen. With laparoscopic obesity surgery these risks are very low – although deep abdominal infections are serious if they occur.

Injury: The insertion of laparoscopic ports and instruments can result in injury to bowel or other organs (eg spleen).

Risks specific to Obesity surgery

Leak: A leak from a staple line (where bowel has been divided or joined to another piece of bowel) is a major and serious complication that increases the risk of death, might result in further surgery, and significantly increases the length of stay in hospital.  The risk of a leak is 1 – 2%.

Conversion to open (non-laparoscopic) surgery: Very occasionally (<2%) technical difficulties or complications encountered during the procedure may require conversion from a key-hole (laparoscopic) operation to an open operation requiring a large abdominal incision.  Were this to occur this would significantly prolong both in-hospital and subsequent recovery.

Vomiting / dehydration: This can occasionally occur (<5%) due to the new small stomach volume or twisting of the narrow stomach tube (Sleeve).  It is usually self-limiting.

Medical and Anaesthetic Risks

Deep Vein Thrombosis (DVT) / Pulmonary Embolus (PE): A DVT is a blood clot that can form in the leg veins causing pain and leg swelling.  The risk of this occurring is approximately 1%. Very occasionally these clots can break off and travel up to the lungs (PE) which can cause death. Multiple precautions are taken to prevent DVTs but the risk cannot be eliminated altogether.

Pneumonia / Chest infection: Rare. Severe chest infections require breathing support in an Intensive Care Unit.

Heart attack or abnormal heart rhythm


Urinary tract infection





While obesity surgery is safe – it is a major operation. Published mortality (death) rates range from 0.05 – 0.2%.  The risk of death is slightly higher for Gastric Bypass compared to Sleeve.

Long-term concerns

Nutritional problems: All obesity operations reduce the intake of nutrition into the body.  This of course, is the desired outcome – but needs to be monitored carefully.  Too much weight-loss is dangerous. Additionally, nutrition and water are essential for life! Problems can arise if not enough fluids are being taken in, or vomiting continues longer than expected, or if the body is not receiving nutrients that are absolutely essential (eg vitamins). Each problem might have a variety of causes, and following surgery, you will be carefully monitored out to two years. Nutrition related risks include:

  • Excessive or inadequate weight loss
  • Nausea and Vomiting: It is not uncommon for patients to temporarily have episodes of vomiting after surgery. Occasionally this may continue intermittently for 2 – 3 months.  Vomiting is usually due to the new, much smaller, stomach capacity. It fills up very quickly! Changes in how you eat are essential and will be extensively discussed with both Dr Mafi and your dietician.  Following their advice should largely prevent this from occurring.  However, if you are not keeping anything down for more than 12 hours you must notify your surgeon. Occasionally, other reasons can cause vomiting (such as twisting or swelling of the narrow stomach tube) which occasionally require intervention.
  • Nutritional deficiencies: All weight-loss surgery can cause deficiencies of essential nutrients such as vitamins.  This is especially true of Gastric bypass.  The most common deficiencies are Calcium, Iron, vitamin D, and vitamin B12. All bariatric patients should have lifelong routine nutritional monitoring (via blood test).  Multivitamins (+/- Vitamin B12 injections) are recommended for all patients – but are especially important in the first year following surgery.
  • Dehydration and/or electrolyte disturbances: Typically results from inadequate fluid intake. Rarely may require admission to hospital to correct.
  • Lethargy and tiredness

Altered bowel habit: This is common.  Often bowel motion frequency is reduced – you might only go once every few days.  This will be especially true prior to reintroducing solid food back into your diet. Sometimes laxatives might be required.

Acid reflux (Gastric Sleeve only): Approximately 20% of people who undergo a Sleeve will get worsening reflux symptoms.  

Bowel obstruction from Internal hernia (Bypass only): A gastric bypass involves rearranging the normal anatomy of the gastrointestinal tract. This creates potential areas that bowel can slip into and “kink” off – causing obstruction.  This complication is uncommon (1-2% risk in the first 2 years after surgery).

Gallstones: Rapid weight-loss sometimes cause formation of gallstones which occasionally cause problems.  If symptomatic this might require removal of the gallbladder.

Psychological: Undergoing obesity surgery is a major operation that results in drastic lifestyle changes.  The surgical journey is universally accompanied by an emotional journey – and it is not uncommon for patients, 1 month down the track, to wish they had never gone through with it. The good news is that 12 months after the operation the vast majority of people report satisfaction and significantly improved quality of life.  

However, occasionally obesity surgery can lead to worsening, or the development of, mental health illnesses including Depression, Anxiety, Adjustment Disorder and very rarely suicide. It is mandatory for all patients considering bariatric surgery to meet with a psychologist at least once prior to deciding whether or not to proceed with surgery.  

Hernia: These are defects in the muscle wall of the abdomen where surgical incisions were made and can result in a lump developing under the skin that can sometimes be painful. Risk of this is low and hernias can be repaired subsequently if required.

“Dumping syndrome”: This is a number of symptoms that can result because food or fluids (especially if they contain high sugar content) moves too quickly (gets “dumped”) from the stomach into the small intestines. The sudden increase in volume in the intestines, along with the subsequent rapid absorption of (especially) a lot of sugar, results in a constellation of symptoms that may include abdominal pain, bloating, sweating, nausea, diarrhoea, and feeling faint or dizzy. Dumping Syndrome is more a risk after gastric bypass than gastric sleeve. It is largely avoidable with diet modification and the avoidance of certain trigger foods and drinks.

The patient journey

Recovery after surgery

In Hospital

Day of surgery:

You will wake up in the recovery unit. There will be multiple monitoring devices connected. You will also have two IV lines and sometimes a urinary catheter.

When recovery staff deem appropriate, you will be transferred to the ward (or occasionally the High Dependency Unit(HDU)

Key medical interventions on the ward (Day 0)

  • DVT (clot) prevention: This is achieved through compression (TED) stockings, Flowtron calf compression pumps, and Clexane injections
  • Pain relief
  • Regular anti-nausea medication
  • Regular anti-acid medication

Key patient objectives on the ward (day 0)

  • Encourage early mobilisation (up-to-chair)
  • Deep breathing exercises
  • Sips of water up to 30mls/hour

Day 1 post op:

The first day after surgery is primarily about increasing mobility and gradually increasing the volume of fluid you can tolerate

You will move to the ward if in HDU

You will be reviewed by Dr Mafi and by a physiotherapist during the day

Key medical Interventions (Day 1)

  • Physiotherapy and guided mobilisation
  • IV medication switched to oral medication (including pain relief)
  • Remove urinary catheter if present
  • Stop IV fluids once oral fluids reaches 60mls/hour
  • Continue all anti-blood clot measures

Key patient objectives on the ward (Day 1)

  • Aim to slowly drink 1L of water over the day (gradually increasing rate up to 100mls/hour)
  • By the afternoon introduction of milky fluids such as nutritional supplementation drinks
  • Increase mobility (short walks)
  • Continue deep breathing exercises

Sometimes, if patient comfortable and meeting all fluid targets, discharge on Day 1 may be possible

Day 2 post op:

This is about consolidating recovery progress and ensuring safe discharge

If not already reached, oral fluid intake should increase to 100mls/hour and nutritional supplementation drinks introduced

Increase frequency and distance of walks (Physiotherapist input)

Most patients will be ready for discharge on Day 2

At home:

Patients will be discharged with a prescription for a variety of medications:

  • Simple pain relief
  • Anti nausea medication
  • Anti acid medication
  • Multivitamin supplement
  • +/- laxative

All medications should be crushed (or capsule opened) during the first 4 post-operative weeks

Continue to take all your usual medications that you were on on before your surgery

TED stockings must be worn for a total of 10 days after your surgery

Refrain from alcohol and fizzy drinks for at least 3 months

Return to work:

Most people will be ready to return to work by 2 weeks

No heavy lifting (> 5kg) for 6 weeks

Dietary Instructions for when you get home:

Your post-operative diet will be dramatically different than before surgery. Over the first four weeks it will gradually progress from fluids, to pureed food, to a soft diet, to small modified meals. During all these stages it is important to:

  • Avoid drinking any fluid with meals
  • Aim for a diet that is high in protein and low in fat and sugar
  • Ensure that you are drinking enough water (1.5-2L/day)

The table below gives a limited overview of what can be expected.  The dietician will discuss in detail what foods are appropriate.

paying by insurance

I am a Southern Cross affiliated provider

If you are insured by Southern Cross then your surgery may well be covered under you plan. We can discuss options with you when we have our first consultation. Dr Mafi is a Southern Cross affiliated provider.

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