Viewpoint - Dietary issues and weight loss surgery

Weight-loss surgery works best when patients adhere to dietary advice, both preand post-operation, as well as undertaking lifestyle changes.

All procedures require patients to make dietary changes as well (Photograph: SPL)

The cost of obesity in terms of quality of life and health and economic costs in society is increasing.

The WHO predicts that by 2015, 700 million people globally will have a BMI of 30kg/m2 or greater. In the face of such staggering statistics, weight loss surgery is being used as a financially viable option. But it is not a quick fix and diet remains a pivotal part of weight management.

Surgical procedures leading to weight loss originated in the 1950s but it is only recently that they have become an integral part of obesity management.

A recent study reported a 10-fold rise in bariatric surgery in the past decade in the UK, from 238 procedures in 2000 to 2,543 in 2007.1 This may be due to increased patient demand and surgical expertise.

Risk of mortality
Indeed, bariatric surgery does reduce risk of all cause mortality, hospital admission and long-term cost to the health service. Patients have been shown to have an improvement or resolution of comorbidities after bariatric surgery. Consequently, a procedure costing around £7,000 could be cost-effective if it reduces a need for long-term management.

Furthermore, a systematic review concluded that surgery is superior to conventional weight-reducing treatment in terms of effective weight loss. However, one surgical technique has not been singled out as being superior to the others.

NICE published guidance on bariatric surgery as part of its clinical guideline on obesity.2 The guideline recommends surgery as a treatment option for adults with morbid obesity (BMI more than or equal to 40kg/m2) or a BMI of 35kg/m2 accompanied by coexisting disease that could be improved by weight loss.

The guidelines say that surgery should be considered only when all non-surgical weight loss treatments have failed.

Crucially, patients must also commit to long-term follow-up, ideally in a comprehensive patient pathway, which can involve dietician-led clinics.

For patients with a BMI of 50kg/m2, surgery can be considered as a first-line treatment.

Surgical procedures
Traditionally, surgical procedures for weight loss have been described as restrictive or malabsorptive, although with greater understanding of the pathophysiology of obesity it is known that gut hormones play an important role.

No bariatric surgical procedure is an easy option and success depends, in part, on the commitment of the patient.

The procedures available include: adjustable gastric band, sleeve gastrectomy and Roux-en-Y gastric bypass, which are all restrictive procedures with little or no nutrient malabsorption; long-limb gastric bypass and duodenal switch (biliopancreatic diversion with duodenal switch), are both restrictive procedures which also cause malabsorption.

Dietary issues pre-surgery
For many people, bariatric surgery is considered when diet has been an issue for many years and various dietary means of weight reduction have been tried without success.

Patients may therefore be surprised to learn that even with surgery, diet remains an important part of treatment to ensure success. Patients being considered for bariatric surgery need to understand the lifestyle changes involved.

Consequently, it is important for patients to be well prepared before surgery. Dietitians have a crucial role to play in care pathways. In Leeds, for example, specialist bariatric dietitians lead community-based weight-loss programmes, which prepare patients for surgery.3

Studies have shown it is useful to follow a pre-operative diet, which is low in calories and carbohydrate for seven to 10 days. These diets reduce the size of the liver, making it easier to perform the surgical procedure.4

Dietary issues post-surgery
Depending on the procedure, the dietary advice given post-surgery can vary. However, all procedures require patients to make significant changes to their diet initially.

Texture needs to be modified, progressing from liquid to purees and then more normal foods. Certain textures may remain a problem for some time, for example tough roasted meat and bread may get stuck.

Patients must learn to slow down and chew well to lessen the risk of regurgitation. The input of the dietitian at this stage is crucial.

Longer term, procedures leading to malabsorption may require specific advice on nutritional supplements. For example, the Roux-en-Y gastric bypass can affect calcium, iron and vitamin B12 absorption and requires a multivitamin and mineral supplement and vitamin B12 injections. In contrast, the gastric band does not lead to malabsorption, but a well-balanced diet is vital to ensure the smaller quantities of food eaten are still nutritionally adequate.

In the case of a gastric band, patients return for band fills until the band is sufficiently restrictive to eat a balanced diet and lose weight. Over-restriction can lead to a poor diet.

For all procedures to succeed, improving quality of life and cutting the cost of managing comorbidities, short-term and long-term support is needed to achieve the best results.

Useful websites

1, Burns EM, Naseem H, Bottle A et al. Introduction of laparoscopic bariatric surgery in England: observational population cohort study. BMJ 2010; 341: c4296.

2. NICE. Obesity: guidance on the prevention, identification, assessment and management of overweight and obesity in adults and children. CG43. London, 2006.

3. O'Kane M, Barth J, Dexter S et al. Improving the bariatric surgical pathway, the Leeds approach. Br J Surg 2008; 95: (Suppl 7).

4. Fris R. Preoperative low-energy diet diminishes liver size. Obes Surg 2004; 14: 1165-70.

  • Dr Phillips is an independent registered dietician

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