07 January 2021

Section 3: How does a gastric band work?



The Gastric Band is an inflatable silicone ring that is placed approximately 1-2cm below where the oesophagus (pipe that leads from the mouth to the stomach) meets the stomach.



Figure 3: Illustration of where the band and port are situated in relation to internal organs




Figure 4: Model of the stomach, band and port. (Exact appearance of port and band will vary depending on brand of gastric band).


The band requires ‘adjustment’ by inflating or deflating its inner surface. A sterile saline fluid (a salty solution like other fluids in your body) or sometimes contrast solution (which can be seen on an x-ray) is used to inflate the band.


A syringe attached to a special needle is inserted into a port attached to the band by thin tubing. The access port is placed just under the skin and fat and stitched to a muscle. It is usually positioned close to the breast bone or ribs.








Figure 5: Illustration of the needle and port during a band adjustment (exact appearance of port will vary depending on brand of gastric band)


Your surgeon may or may not inject some fluid into the band at the time of surgery. This can cause a reduction in appetite and portion sizes. However, this reduction is not expected to last and you are likely to find that your appetite returns any time from a few days to 2-3 weeks after surgery. This is normal.


After a minimum of five weeks, the band is adjusted for the first time. In most cases, this is performed by one of our Specialist Bariatric Nurses or Specialist Bariatric Dietitians in clinic. You will need to attend clinic regularly for assessment and possible further adjustment of the band.


It is usual to need between 4 and 6 adjustments to the band in the initial 6 months post-surgery before it is appropriately/optimally adjusted. You may find that you feel a change after band adjustments, but it eases off within 1-2 weeks; this is normal and due to the loss of fat around the stomach. It is important to remember that everyone is different and a small minority of people can even feel the effects of the band with only 1 or even 0 adjustments. It is not the case that the more adjustments you have, the more weight you lose.


You may need any amount of fluid in your band to achieve the desired effects described below,  as the amount needed is individual.  It is important to trust the judgement of your Specialist Dietitian and Specialist Nurse with regards to the amount of fluid that you need for your band to be at its optimum.


See Section - Gastric Band adjustments for further information on band adjustments.


How A Gastric Band Works


Remember, the band only starts working once it is adequately adjusted.  How much fluid needed for this to be the case is entirely individual.


In the past, it was assumed that the band caused meals to pile up in the small pouch of stomach above the band, thereby “restricting” the volume consumed to whatever would “fit” into the small pouch. This small volume of food was thought to stretch this area of the stomach and make you feel full. The gradual emptying of the food into the remainder of the stomach was thought to be what prolonged this fullness/satisfaction between meals.


Studies performed in 2010-2011 confirmed that the mechanism is actually a lot more complex than this. They showed that the band, at the optimal volume of fluid, does not cause food to rest above the band. Rather, it works in two main ways:


  1. It compresses the top of the stomach. This is why it is placed so high up. This compression causes certain nerve endings in your stomach wall to be stimulated, which effectively ‘tricks’ your brain into thinking your stomach is full.  In other words, it means your appetite is permanently reduced.



Figure 6: Illustration of the band’s position at the very top of the stomach and its compression of the specific nerve endings found in that area (exact appearance of band will vary depending on brand)


    2. It creates a small 1-2cm space above the band (space for just one small mouthful of food) and a small gap between this             space and the bottom of the stomach.


When it is time for a meal, you naturally begin to feel hungry. You then need to eat, but in a very specific way – the ’20, 20, 20, 20 rule’:


  • Take a bite of food the size of a 20 pence piece (using children’s cutlery can help). Chew it for at least 20 seconds, and then swallow.


  • Wait at least 20 seconds before taking your next mouthful.


This is because the oesophagus (the tube running from your mouth to your stomach) needs a minimum of 40 seconds, and up to 60 seconds, to squeeze a mouthful of food entirely through the band. 


With each squeeze of the muscles in the oesophagus, some of the mouthful of food will push its way through the band. This stimulates the nerve endings described above even more.


A mouthful can need anywhere between 2 and 6 ‘squeezes’ to get it through the band. 


Generally, the more solid the food, the greater the number of ‘squeezes’ needed to get it through the band. 


More ‘squeezes’ = more nerve ending stimulation (see How to Get the Most Benefit from Your Gastric Bandbelow).


  • Repeat 1) and 2) for a period of 20 minutes (no longer) and then stop.  By this point, you will have consumed around 20 small mouthfuls of food and the nerve endings will have received up to 120 signals, if you chose solid, textured food.


  • Rest for a 10-15 minutes. If you chose solid, textured food, you should then find that you no longer feel hungry and so will have achieved ‘satiation’ (satisfaction). This is because the stimulation given to the nerve endings in the stomach wall will have been strong enough to make your brain think that your stomach is full.


It is crucial that you understand that this sensation is not a blocked up / “stuffed” feeling,that is the portion of stomach above the band is not filled with food. Because of this,  the band will never physically stop you being able to continue eating once no longer hungry. Focus on the fact you no longer feel hungry and therefore do not need to eat any more.


Smartphone apps such as “Bariatric Meal Timer” (Apple), “20 Minute Eating” (Apple) and “Time Your Bites” (Android) can be helpful in following the ‘20/20/20/20’ rule.


Figure 7: The oesophagus squeezing a mouthful of food through the band (exact appearance of band will vary depending on brand)


If the band is “over-adjusted” (tightened up too much), or you do not follow the ‘20/20/20/20’ rule, then food does accumulate in the pouch above the band.  Symptoms of this would include a “stuck” / heavy / tight feeling or pressure, which tends to be uncomfortable or even painful.  You may also feel the need to regurgitate the food. See: Common Problems.


If the band is “under-adjusted” (contains insufficient fluid), then the nerves are not stimulated enough. You won’t feel satisfied between meals and will be able to eat more quickly, take larger bites and therefore a larger volume of food in 20 minutes.



How to Get the Most Benefit from Your Gastric Band


Initially after the surgery, you must follow a special diet for 4 weeks, which consists of:


Weeks 1 & 2: fluid diet

Weeks 3 & 4: soft diet


This enables the band to settle into position whilst preserving its structure. Solid food must be avoided during the first 4 weeks as it may cause the very small portion of the stomach that is above the band to stretch and/or put pressure on the stitches, potentially resulting in band slippage (see Risks & Complications). 


Liquids and soft foods are squeezed very easily through the band, which gives the area around the band a chance to heal and reduces the risk of complications. 


However, because minimal ‘squeezing’ is required to get liquids and soft food through the band, minimal signals are sent to your brain to reduce your appetite.  Remember that this means it is normal to begin to feel hungry fairly soon after the operation. It does vary from person to person. Appetite can return any time from 1 day to several weeks after the operation.


From 5 weeks post gastric band surgery onwards, it is essential that you progress onto a diet of solid/textured foods.


In order to lose weight, the key messages at this stage are:


  • Choose chewable solid/ textured food



  1. Portions will be smaller (if you limit your meal to 20 minutes). This is because there is a greater chance that you will have to:
    • Take small mouthfuls
    • Chew properly
    • Rest between mouthfuls


  1. You will feel satisfied for longer. This is because it is thought that the number of times the oesophagus has to contract (i.e. the number of ‘squeezes’ that are needed) to get a mouthful of solid/textured food through the band is up to three times greater than with a mouthful of soft food/liquid food.


x    Avoid soft food or ‘liquid food’



  1. Portions will be larger. This is because there is much less need to follow the ’20, 20, 20, 20 rule' – you can manage larger mouthfuls, less chewing is needed and you can eat more quickly.
  2. You will feel satisfied for a shorter amount of time. This is because the oesophagus can squeeze this type of food through the band very easily and quickly and so up to two thirds fewer signals are sent to your brain.

REMEMBER: Even if you are eating solid foods, a reduction in appetite and portion size is unlikely to occur to any great degree until the band is optimally adjusted. On average, 4-6 band adjustments are needed for this to occur.





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