The role of very low calorie diets

Can these controversial diets have a role in the complex problem of obesity, asks Dr Frankie Phillips.

Studies suggest that patients can lose between nine and 26kg during the VCLD course
Studies suggest that patients can lose between nine and 26kg during the VCLD course

Very low calorie (or energy) diets (VLCDs) are defined, according to the international Codex standardisation and the European Union, as total diet replacements with an energy content between 450 and 800kcal/day.1, 2

They are intended as a complete source of nutrition to be consumed as the sole dietary intake and contain all essential vitamins, minerals, electrolytes and fatty acids.

VLCD formulations are usually liquid or powders made up with water, but solid bars are also available. VLCDs are different from meal replacements, which are intended to replace one or two meals per day only.

Recommendations for use
According to NICE clinical guidelines, VLCDs (less than 1,000kcal/day) may be used continuously for a maximum of 12 weeks, or intermittently with a low-calorie diet.3

Any diet of less than 600kcal/day should be used only with clinical supervision.

The guidelines recommend that VLCDs should only be used by adults who are obese (BMI> 30kg/m2) and have reached a plateau in weight loss.

Certain groups and those with some medical conditions are advised not to use VLCDs (see box below). In the longer term, healthy eating advice should be followed to achieve a balanced diet. A typical diet plan includes three or four products to be consumed every day. The supervision of a healthcare professional is recommended.

Contraindications for VLCD use
  • Infants and children
  • Adolescents
  • Pregnant and lactating women
  • Elderly
  • Unstable cardiac or cerebrovascular disease
  • Acute and chronic renal failure
  • Severe or end stage liver failure
  • Acute psychiatric disorder
  • Gout

 

DRUG MANAGEMENT DURING VLCD USE6
Drug categoryAction
Insulin or hypoglycaemic agentReduce or stop then check control (normally at the lower dose)
Antihypertensives Stop diuretics initially; reduce dose of other antihypertensives depending on monitored values
Oral anticoagulantsContinue pre-diet dose but monitor INR frequently and modify dose if necessary
Lipid-lowering drugs Stop or decrease (except familial conditions)
Drugs for angina, asthma, epilepsy, depression and anxietyContinue as normal

Benefits and concerns
VLCDs are controversial, but if used appropriately, they can lead to rapid weight loss compared with conventional low-calorie diets. Such rapid weight loss might be desirable if an obese patient needs to lose weight urgently, for example, in preparation for surgery.

Studies suggest that weight loss of 1.5-2.5 kg per week in the short term may be expected, with 9-26kg being possible during the course of a VLCD programme.4-6

In addition to rapid weight loss, VLCDs can be effective at improving other conditions, in particular cardiovascular disease risk factors. Improvements have been observed in triglyceride and LDL-cholesterol as well as improved glycaemic control and insulin resistance.7

However, a Cochrane systematic review found VLCDs were no more effective than conventional non-pharmacological weight loss interventions in type-2 diabetes management.8

Early versions of VLCDs were associated with the danger of total starvation owing to very restricted diets (400kcal/day) and the 1970s saw cases of cardiac dysrhythmias and sudden unexpected death.

VLCDs are unlikely to cause harm in otherwise 'healthy' obese people. However, they are only intended to be a short-term option when other weight loss attempts have not succeeded.

The main disadvantage of VLCDs is that they do not necessarily incorporate behaviour modification to develop a healthy long-term relationship with food; consequently, many patients regain weight.

Long-term sustained weight loss after VLCD has been questioned and studies have shown that 25-35 per cent of individuals maintained a clinically significant 10 per cent weight loss up to seven years, but most returned to pre-treatment weight.9-11

A systematic review of studies has shown that maintenance of weight loss is improved by using VLCD as part of a weight management programme including behaviour modification as part of follow up.12

In a meta-analysis of more than 400 studies of VLCD, side-effects were generally considered to be minor in those who were otherwise healthy.2

Typically reported side- effects include dry mouth, constipation, diarrhoea, nausea, headache, muscle cramps, hunger, cold intolerance and dry skin. However, other more serious side-effects have been reported with VLCD, including acute gout, cholelithiasis and acute psychosis.

The existence of comorbidities can lead to complications and those on a range of drugs must be managed with some doses requiring adjustment (see box left).6 To minimise risks of VLCD, guidelines on using the product need to be adhered to.

Safety aspects such as making up 'drinks' with the correct amount of water will prevent electrolyte imbalance.

The role of the GP
It is vital GPs are aware that VLCDs are not appropriate for all obese patients. Nevertheless, VLCD products are available without prescription, and while monitoring by a healthcare professional is advised, it is not guaranteed.

Managing an obese patient on a VLCD is an important role and education and support can help with motivation and successful weight loss maintenance.

GPs should be clear that the initial rapid weight loss from a VLCD is only one step in tackling the problem of obesity.

Conclusion
Although generally safe in the short term, VLCDs should not be seen as a first-line treatment and are only suitable for those with a BMI greater than 30kg/m2.

VLCD should be used as part of a complete weight management strategy among the well-motivated. A more holistic approach is necessary for a complex problem such as obesity. Contraindications should be reviewed and manufacturers' guidelines adhered to.

  • Dr Phillips is an independent registered dietician based in Devon

MEDICO-LEGAL CONSIDERATIONS

The MDU is approached by GP members concerned about the medico-legal implications of providing medical supervision for patients taking part in slimming programmes involving a VLCD.

The GMC requires that doctors provide effective treatments based on the best available evidence and GPs are required to provide, under the NHS, all appropriate and necessary medical treatment of the type usually provided by a GP.

The GMC requires doctors to work within the limits of their competence. GPs who agree to supervise patients on VLCD must have the requisite knowledge and be familiar with any contraindications, possible adverse effects and requirements for adjustment to any medication the patient is taking.

'Referral' has a very specific meaning in the medical context.

GPs referring a patient to a nutritional specialist might wish to ensure the specialist is a healthcare professional regulated by a statutory regulatory body. If they are not, the transfer of care may be regarded as delegation, not referral, which means the doctor will remain responsible for the overall management of the patient (Good Medical Practice, GMC, paragraph 55).

  • Dr James Armstrong, MDU medico-legal adviser

References

1. CODEX STAN 203-1995. Standard for formula foods for use in very low energy diets for weight reduction. www.codexalimentarius.net

2. SCOOP report. Reports on tasks for scientific cooperation. Collection of data on products intended for use in very low calorie diets. Report of experts participating in task 7.3. September, 2002.

3. NICE Guidance on the prevention, identification, assessment and management of overweight and obesity in adults and children. 2006. www.nice.org.uk/CG043

4. Wadden TA, Stunkard AJ, Brownell KD. Ann Intern Med 1983; 99: 675-84.

5. Anderson JW, Konz EC, Frederich RC, Wood CL. Am J Clin Nutr 2001; 74[5]: 579-84.

6. Mustajoki P, Pekkarinen T. Obes Rev 2001; 2[1]: 61-72.

7. Capstick F, Brooks BA, Burns CM. Diabetes Res Clin Pract 1997; 36: 105-11.

8. Norris SL, Zhang X, Avenell A, et al. Cochrane Database of Systematic reviews 2005; 2. Art No:CD004095.

9. Wadden TA, Frey DL. Int J Eat Disord 1997; 22[2]: 203-12.

10. Pekkarinen T, Takala I, Mustajoki P. Int J obes 1996; 20: 332-7.

11. Andersen JW, Vichitbandra S, Qian W, Kryscio RJ. J Am Coll Nutr 1999; 18[6]: 620-7.

12. Ayyad C, Andersen T. Obes Rev 2000, 1: 113-9.

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