It is important to encourage a degree of healthy weight loss in anyone with type 2 diabetes who is overweight, except where there are other associated risks (eg in the frail and elderly, or those with eating disorders). Because a healthy body weight is sometimes not achievable, setting this as a goal might discourage patients from attempting any dietary change.
The Australian Obesity Management Algorithm is a practical clinical tool to guide the implementation of existing guidelines for the treatment of obesity in the primary care setting in Australia.
Assessing weight is typically done using BMI, which can be a difficult parameter to standardise between different population groups.
For those of European descent, a healthy BMI is 18.5–24.9 kg/m2, overweight is 25–29.9 kg/m2 and obese is ≥30 kg/m2.6 Different classification criteria may apply to other population groups. Some groups may have equivalent levels of risk of health problems at a lower BMI (eg these BMI thresholds should be reduced by 2.5 kg/m2 for patients of Asian ethnicity7) or higher BMI (eg Torres Strait Islander and Maori peoples).30
It is advisable to also assess waist circumference (in centimetres), as this is a good indicator of total body fat and a useful predictor of visceral fat. Waist circumference of ≥94 cm in men and ≥80 cm in women conveys increased risk of obesity-related complications; ≥102 cm in men and ≥88 cm in women convey high risk.31 As with BMI, these values may differ for other population groups.6
Measuring waist circumference in patients with a BMI >35 kg/m2 may not add any further to predictive disease risk classification.32
Lifestyle interventions for weight management
In overweight or obese people with diabetes, a nutritionally balanced, energy-reduced diet should be recommended if a lower, healthier body weight is to be achieved and maintained as part of a multi-component lifestyle intervention (including healthy eating, physical activity and support for behavioural change).
Very low energy diets (VLEDs) can be considered as an initial weight loss strategy, when supervised lifestyle interventions have been unsuccessful in reducing weight, or when rapid weight loss is required (eg prior to bariatric or general surgery that is conditional on weight loss).33 These diets may be considered in adults with diabetes with BMI >27 kg/m2, taking into account each individual situation.34 A primary care–based weight loss study, the Diabetes Remission Clinical Trial (DiRECT), showed that VLED with associated weight loss led to 46% of participants reducing or ceasing diabetes medications after 12 months of intervention.35
VLEDs require regular appointments with appropriate health professionals to support the progress of the individual. Caution should be exercised if hypoglycaemia is a risk (people taking sulfonylureas and insulin). Use of sodium glucose co-transporter 2 (SGLT2) inhibitors in people on VLEDs or any high-protein, low-carbohydrate diet is not recommended (due to raised risk of ketoacidosis, which might be euglycaemic).
Pharmacotherapy is licensed by the Therapeutic Goods Administration (TGA) for weight management, including for patients with diabetes, but is not currently reimbursed by the Pharmaceutical Benefits Scheme (PBS). There are now four drugs that can be used as adjuncts to dietary changes and physical activity improvement: phentermine (a sympathomimetic amine), orlistat (an inhibitor of intestinal lipase), liraglutide (a glucagon-like peptide-1 receptor agonist [GLP-1 RA]) and combined naltrexone and bupropion.
These drugs may be considered in adults with diabetes with BMI ≥27 kg/m2, taking into account each individual situation.33
Each drug has the potential for significant clinical side effects and contraindications associated with its use. They require careful clinical risk–benefit assessment when applied in practice. Refer to the TGA website for more information.
Surgery for weight loss, also called metabolic or bariatric surgery, may induce weight loss in people who have failed by other means. The following procedures are used in Australia.7,34
- Sleeve gastrectomy involves removing the greater portion of the fundus and body of the stomach, reducing its volume from up to 2.5 L to about 200 mL. This procedure provides fixed restriction and does not require adjustment like laparoscopic adjustable gastric banding (LAGB).
- Roux-en-Y gastric bypass is a combination procedure in which a small stomach pouch is created to restrict food intake and the lower stomach, duodenum and first portion of the jejunum are bypassed to produce modest malabsorption of nutrients and thereby reduce kilojoule intake.
- Biliopancreatic diversion is also a combination procedure that involves removing the lower part of the stomach and bypassing the duodenum and jejunum to produce significant malabsorption. This procedure tends to be performed in subspecialty centres.
Used in the past, LAGB is less used now in Australia and North America due to less sustained weight loss, fewer metabolic benefits and high surgical complication rates. This procedure involves placing a band around the stomach near its upper end to create a small pouch.6
Sleeve gastrectomy, Roux-en-Y gastric bypass and biliopancreatic diversion lead to sustained weight loss and normalisation (refer to ‘Practice Point’ above) of type 2 diabetes metabolic markers, although techniques vary in efficacy.6
The improvement in diabetes metabolic markers for Roux-en Y gastric bypass surgery at two-year follow-up was 52.7% in one meta-analysis, compared with 0.7% for medical management.36 For individuals who achieve improvement in diabetes metabolic markers with Roux-en-Y gastric bypass, the median period of sustained improvement is 8.3 years.7
Metabolic surgery in patients with type 2 diabetes is associated in non-randomised studies with reduction in microvascular and macrovascular complications as well as reduced mortality.7 Moreover, studies have also shown that metabolic surgery can prevent or delay the onset of type 2 diabetes in people with obesity.7
Taking into account each individual situation, metabolic surgery may be considered for people with a BMI >30 kg/m2 who have suboptimal BGLs, are at increased CVD risk and are not achieving recommended targets with medical therapy.7
GPs should assess the appropriateness of metabolic surgery for each individual patient and provide information on the risks, benefits and appropriateness of the type of procedure. Metabolic surgery performed in a high-volume specialist centre with an experienced surgical team may offer the lowest risks, and GPs should liaise with a specialised surgical team if there are concerns.33,34
Metabolic surgery, when indicated, should be included as part of an overall clinical pathway for adult weight management that is delivered by a multidisciplinary team (including surgeons, APDs, nurses, psychologists and physicians), and includes planning for surgery and continuing follow-up.33
Adverse events of metabolic surgery, particularly in the long term, need more research;37 however, suggested follow-up care includes monitoring for nutritional deficiencies and acid reflux disorders.38
Women of reproductive age who have had metabolic surgery need particular advice on contraceptive choices; those who plan to have a pregnancy need assessment, before and throughout pregnancy, regarding nutritional status, need for higher multivitamin dosages and close obstetric monitoring. Referral prior to pregnancy to appropriate specialty services is strongly advised, even if the diabetes appears well managed.