Introduction

For many decades, it has been known that the dietary health of a population is associated with the incidence of disease. International guidelines produced by the World Health Organisation and other governmental bodies advise a balanced diet. Bariatric and metabolic surgery can alter this balance through inhibiting the absorption of nutrients and altering an individual’s choice of food. Therefore, all post‐bariatric surgical patients require lifelong monitoring and appropriate nutritional supplementation to prevent deficiencies that could lead to disease.

Each metabolic and bariatric surgical procedure poses a separate nutritional challenge in regard to nutrient absorption or food avoidance. Therefore, post‐surgical dietary recommendations and supplementation are tailored to each surgical procedure.

It is important to consider an individual’s presurgical nutritional status in order to avoid making pre‐existing nutritional deficits worse in the post‐operative period. All pre‐operative patients should be screened for nutritional deficiencies prior to bariatric surgery, and all identified deficiencies should be corrected. Occasionally, pre‐surgical nutritional deficiencies require further investigation to determine their aetiology, e.g. iron deficiency anaemia, which could be due to dietary iron insufficiency from veganism or due to gastrointestinal malignancy (Figures 23.1 and 23.2).

The incidence of multiple nutritional deficiencies in the obese population is relatively high due to the combination of the consumption of high‐calorie foods that have low nutritional value and immobility. Immobility leads to the lack of natural light that in turn results in vitamin D deficiency. As vitamin D, iron and B12 deficiencies are common in pre‐surgical candidates, it is advisable to commence multivitamins with mineral supplements prior to bariatric surgery.

Peri‐Operative Nutrition

Prior to bariatric surgery, it is recommended that patients undergo a pre‐operative diet that helps reduce the fatty content of their liver in order to reduce its size by 10–20%. A reduction in the size of the liver aids the ability to lift the liver during surgery and reduces the risk of peri‐operative complications. Liver‐shrinking diets usually involve a very low calorie diet with limited nutritional content so prophylactic vitamins and mineral supplementation are required. These pre‐operative low‐calorie diets can be particularly problematic for people with type II diabetes. The sudden reduction in the total oral intake of carbohydrates could potentially lead to hypoglycaemia in those patients on medications.

In the post‐operative period, there is a gradual reintroduction of a nutritionally balanced diet. Initially, patients are started on a liquid diet moving up to a pureed diet and then soft solids, before hopefully moving onto a normal balanced diet. Advice and guidance is usually required from a specialist dietitian to ensure adequate intake of all major food groups and nutrients occurs with a special focus on fluid intake. This is because there is a high incidence of post‐operative nausea, vomiting and constipation. Without adequate fluid intake, patients can then easily get dehydrated, which is a particular risk to those patients on antihypertensive agents or who have pre‐existing conditions, such as diabetes or chronic kidney disease.

The majority of post‐operative nutritional complications usually occur within the first 12 months post‐surgery. It is therefore essential that patients are regularly followed up by a specialist MDT team with access to specialist dietitians, physicians, surgeons and nutritional support nurses. Usually, nutritional deficiencies are mild and can be corrected by oral supplementation, but occasionally nutritional deficiencies can be so extreme that parenteral nutritional support is required.