Pre‐Operative Management of a Bariatric Patient (Nutritional)

Pre‐Operative Management of a Bariatric Patient (Nutritional)

Lindsay Parry

It is now widely appreciated that with increasing rates and complexity of obesity and obesity‐related co‐morbidities, bariatric surgery is the most clinically and cost‐effective treatment. It is not however without risks. Nutritional risks being a major consideration. This chapter focuses on the nutritional management of a patient preparing for surgery. It is worth noting that pre‐operative preparation for bariatric surgery is managed by a Tier 3 service.

There are 3 main roles of nutritional management when preparing individuals for bariatric surgery: assessment, education and treatment (Figure 10.1).

Schematic illustration of three main roles of nutritional management.

Figure 10.1 Roles of nutritional management.


Pre‐operative nutritional status should be thoroughly assessed for anyone considering bariatric surgery. In‐depth history taking, to include information about previous weight loss attempts, social circumstances, cooking abilities, support networks, employment status and state of dentition will assist in building a picture of the individual and helping to highlight where support may be required; or, if indeed, bariatric surgery would be appropriate. Bariatric surgery requires a lifelong commitment and specific eating behaviours. It is widely recognised that approaching this alone yields less favourable outcomes than if an individual has support. Encouragement should therefore be given to engage the support of family and/or friends at this early stage. There are specific dietary requirements following bariatric surgery, so a basic level of nutritional knowledge and cooking abilities are essential to succeed. It is necessary therefore to establish this in order to be able to signpost individuals with gaps in skills or knowledge to the relevant education before embarking on bariatric surgery. As mentioned later on in this chapter, certain behaviours are vital for success with bariatric surgery so assessing lifestyle and motivation to change will assist in identifying those ready for surgery.

A higher prevalence of nutritional deficiencies is reported in the obese population. This is considered to be the result, primarily, of an unbalanced diet. It is recognised that pre‐existing nutritional deficiencies can result in poorer prognosis and more post‐operative complications. These deficiencies should therefore be investigated and corrected appropriately prior to any surgical intervention.

A verbal detailed dietary assessment can be useful to recognise eating habits and behaviours as well as macronutrient deficiencies; in particular, protein. However, blood tests will be required to screen for micronutrient deficiencies (see Table 10.1).

Additional blood tests, such as fat soluble vitamins and zinc, copper and selenium, may be useful if individuals are being considered for more malabsorptive procedures, such as biliopancreatic diversion, duodenal switch or single anastomosis duodenal‐ileal bypass with sleeve (SADI‐S) due to the increased risk of post‐operative deficiencies. These procedures are not routinely performed at all bariatric centres in the UK and require experienced specialist input.

In view of the prevalence of vitamin D insufficiency and deficiency in the UK population generally, all pre‐operative patients should be advised to take an over the counter vitamin D3 supplement daily of at least 400 IU (10 μg) per day.

Additionally, assessment should include consideration of any existing medical history or dietary restrictions that may impact on nutritional status further down the line, for example, coeliac disease, renal disease, liver disease, vegetarian/vegan diet or lactose intolerance.

Table 10.1 Preoperative nutritional assessment

Preoperative nutritional assessment

  • All people should have a comprehensive nutritional assessment prior to bariatric surgery

  • Check full blood count including haemoglobin, ferritin, folate and vitamin B12 levels
Vitamin D, calcium and parathyroid hormone

  • Check serum 25‐hydroxyvitamin D levels

  • Check serum calcium levels

  • Check serum/plasma parathyroid hormone levels

  • Seek advice from a specialist with expertise in primary hyperparathyroidism if primary hyperparathyroidism is suspected
Vitamin A, zinc, copper, selenium and malabsorptive procedures

  • Consider checking serum vitamin A levels in individuals going forward for malabsorptive procedures such as BPD/DS or where vitamin A deficiency may be suspected

  • Consider checking serum zinc, copper and selenium levels in individuals going forward for malabsorptive procedures such as BPD/DS or if a deficiency is suspected

  • There is insufficient evidence to support a recommendation to screen an individual’s thiamine levels pre surgery; however, some individuals may have low levels

  • There is insufficient evidence to support a recommendation to screen an individual’s magnesium level pre‐surgery
HbA1c, lipids, liver and renal function

  • Routinely screen HbA1c, lipid profile, liver and kidney function tests and treat as necessary
Correction of nutritional deficiencies preoperatively

  • Treat and correct nutritional deficiencies preoperatively as individuals have an increased risk of deficiencies postoperatively


Prior to surgery, it is essential for an individual to understand the importance of certain dietary behaviours to prevent complications.

Dietary assessment should consider an individual’s current nutritional knowledge and knowledge of bariatric surgery. Dietary intake, habits and behaviours should be explored to consider types, frequency and balance of meals, fluid intake and snacking behaviours. Ideally, this should be performed alongside psychological assessment to consider motivation, readiness and ability to make relevant changes and to rule out eating disorders. It is pertinent to establish anticipated weight loss and other patient expectations of surgery, and provide individuals with realistic statistics, for example, expected excess weight loss for each of the offered procedures, what surgery will and will not change (for example gastrointestinal surgery affecting anatomy, gut hormones and appetite will not change mindset), and the risks of being left with significant amounts of excess skin. This should help manage patient‐led goal setting and determine realistic expected outcomes from surgery.

Main considerations are as follows.

Regular Meals

Education about eating regularly is important to ensure adequate nutrition post‐operatively. Although the full mechanisms of the most common bariatric procedures are complex and multifactorial, we understand that surgery physically reduces the size of the stomach pouch and causes biochemical changes in hormone profile, bile acids and microbiome. This results in reduced hunger signals, as well as influences on taste changes making certain food less appealing. Overall volume of intake therefore reduces as does the calorie density of foods eaten. Satiety is reached earlier and lasts longer.

It is therefore very important that a regular meal pattern is established prior to surgery and any barriers that have prevented this are addressed in order to prevent under nutrition and malnutrition post‐operatively.

Portion Size

Overeating is commonly reported by individuals attending weight management services and is often related to portion control and perceptions of a ‘normal’ portion. Whilst this may be improved by encouraging eating regular meals, there are often other influencing factors.

It is commonly reported that individuals have been brought up to clear the plate and will therefore finish any food that has been presented to them disregarding satiety. It is also common for individuals to eat more than is required if they are enjoying the food or not concentrating on the meal – mindless eating.

With the knowledge of how bariatric procedures influence appetite, and the human body’s incredible ability to adapt, it is important to address these behaviours and look at strategies to manage them pre‐operatively to reduce the risk of weight regain following surgery.

Strategies to help individuals slow their eating down such as 20:20:20 (cut food to the size of a 20 pence piece, chew each mouthful 20 times, after 20 minutes of eating discard any remaining food), putting cutlery down between mouthfuls of food to encourage more mindful eating and sitting at a table away from distractions are often helpful approaches.

Slower more mindful eating practices will also help reduce complications, such as food blockages, reflux and regurgitation after surgery.

Meal Balance

The balance of meals is equally important. Reducing overall portion may be less effective if the foods eaten are calorie dense. Establishing an estimate of which macronutrients contribute what percentage to the overall intake is a useful starting point. In order to promote weight loss prior to surgery, the aim is to increase low‐calorie dense foods such as salad and vegetables whilst decreasing amounts of high‐calorie dense foods such as carbohydrates and fats. Focus is also placed on protein in order to ensure a good variety is eaten, in large enough quantities to be sufficient after surgery. It is useful to try and help an individual visualise what they are aiming for, for example, half a plate of salad and vegetables, a quarter of a plate of protein food and a quarter of a plate of complex carbohydrate (Figure 10.2).

Schematic illustration of meal balance.

Figure 10.2 Meal balance.

Source: Africa Studio / Adobe Stock; Source: mates / Adobe Stock; Source: smokedsalmon / Adobe Stock.

By reducing overall energy intake and ensuring intake of complex carbohydrate and more salad and vegetables, the aim is to improve satiety from less overall calories, creating an energy deficit resulting in weight loss and improved glycaemic control.

This is also pre‐emptive of any potential problems that may occur after surgery with dumping syndrome or rapid transit. Dumping syndrome, rapid transit and rebound hypoglycaemia all are commonly recognised complications after bariatric surgery, in particular following gastric bypass (however symptoms can be seen after sleeve gastrectomy). Various terms used to describe the symptoms are often interchanged.

Dumping syndrome includes gastrointestinal and vasomotor symptoms that occur following a meal, in particular carbohydrate rich meals. Symptoms occurring 15 minutes to 1 hour after a meal are considered ‘early dumping syndrome’ and are mainly gastrointestinal (symptoms of diarrhoea, nausea and abdominal cramps). The cause is considered to be due to osmotic effects owing to larger than normal volumes of undigested foods reaching the small intestine too quickly. Symptoms occurring one to three hours after a meal are considered ‘late dumping syndrome’ and are considered to be vasomotor (sweating, lethargy, shakiness, hunger, hypotension and hypoglycaemia). They are caused by reactive hypoglycaemia that is induced by an exaggerated insulin response that overcompensates for the carbohydrate load ingested.

In most cases, dietary adjustments will prevent these symptoms. Dietary advice should include the following:

  1. Smaller regular meals (up to six small meals daily).
  2. Separation of fluid and food (no fluid 20–30 minutes either side of a meal).
  3. Avoid simple carbohydrate and high sugar foods (for example biscuits and sweets).
  4. Include more complex carbohydrate and high fibre food choices (for example wholemeal and whole grain products) and low glycaemic index foods.
  5. Increase protein and fat* content of the diet to compensate for reduced calories from carbohydrate and to help slow down digestion.

    *The fat content of the diet should be increased with caution to prevent any malabsorptive symptoms

If an individual develops the symptoms of dumping syndrome, there is no immediate treatment other than to allow the symptoms to pass. They will resolve spontaneously with time. Symptoms can be so severe that individuals have been known to present at emergency departments believing they are having a heart attack. Prevention is therefore preferable which can be achieved with pre‐operative education; see Chapter 24 for more detailed discussion about dumping syndrome.


Bariatric surgery will result in biological changes, which will reduce appetite and restrict the amount of food an individual can consume in one sitting. It will not improve the nutritional quality of the foods an individual chooses or control how often or why the individual eats.

There is consistent evidence that grazing/snacking behaviour can lead to an overall increased energy intake and weight regain/poor weight loss after surgery. Snack foods tend to have high fat and sugar content but have a low nutritional value, for example biscuits, cakes, crisps and sweets. Often these are consumed for reasons other than hunger. Boredom, emotion, habit and comfort are reasons often cited by individuals engaging in the behaviour.

There are incidences where healthy, planned snacks are helpful, for example when work patterns or other responsibilities require long periods of time between one meal and the next. A planned and controlled snack can be helpful under these circumstances to manage appetite, speed of eating and future food choices and volume at the next planned meal.

Uncontrolled snacking, however, is not beneficial and will lead to weight regain after surgery. Both psychological and dietetic support will be helpful to manage this behaviour.

Fluid Intake

Fluid intake can be challenging following a bariatric procedure both due to the reduced capacity for volume in one sitting and due to the recommendation to separate fluid from food intake by 20–30 minutes.

Gulping fluids can lead to abdominal discomfort and regurgitation following bariatric surgery.

The separation of fluids from food intake is to prevent over fullness from non‐nutritious fluids leading to the potential for malnutrition and also to prevent complications such as dumping syndrome (discussed later).

Individuals are generally encouraged to aim for approximately 2 l of fluid daily assuming there are no medical conditions influencing this.

Inadequate fluid intake will negatively impact on an individual’s bowel and renal function, therefore learning to take regular, frequent sips of fluids between meals pre‐operatively is essential to enable them to consume sufficient fluid post‐operatively.

Types of fluid consumed should be considered. Fizzy drinks can cause bloating and fullness, which post‐operatively may reduce nutritional intake so these are best avoided.

High‐caloric fluids, such as sugary fruit juices and sugary milkshakes/lattes, are also discouraged. These types of fluids will contribute significant ‘empty’ calories towards a daily intake, whilst providing little nutritional value, impacting on weight regain/poor weight loss and are highly likely to trigger dumping syndrome after a gastric bypass.

Alcohol, another high‐caloric fluid, should also be discouraged for this reason. There is increasing evidence that problems with alcohol dependency can occur following bariatric surgery. Whilst it is recognised that more research is needed in the area, pre‐operative alcohol dependence and regular alcohol consumption are considered predictors and should therefore be assessed and flagged pre‐operatively. Additionally, anatomical changes following bariatric surgery combined with alcohol can result in irritation to gastrointestinal mucosa and potentially the development of ulcers. Recommendations therefore should be that alcohol intake is minimised or stopped altogether pre‐operatively, to reduce risk of post‐operative complications.

This information can be summarised for individuals. Special attention should be paid to areas they may need more support with.

The main dietary behaviours are summarised below (Table 10.2).

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May 14, 2023 | Posted by in GENERAL SURGERY | Comments Off on Pre‐Operative Management of a Bariatric Patient (Nutritional)

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