Weight management guidelines and the first law of thermodynamics
The first law of thermodynamics states that energy can be transformed (changed from one form to another), but cannot be created or destroyed.13 In the context of humans or other animals this means that the energy stored by the body must equal (over time) energy intake minus energy expenditure. This simple law of nature, often referred to as the energy balance equation, means that interventions aiming to reduce weight must either reduce calorie intake (metabolisable energy intake), increase energy expenditure (in practical terms by exercise), or both. NICE and all other past and future guidelines on weight management are thus bound by this equation. It is not surprising then that NICE guideline 43 and other guidelines on weight management and obesity contains evidence reviews across these key components of diet and exercise, and behavioural change methods that may help either or both.
How relevant are the NICE guidelines on obesity to UK primary care?
The NICE guidelines are the most comprehensive and thorough of recent guidelines, with the full guideline running to a daunting 1942 pages (which presumably few GPs or primary care staff have the time or energy to read). However, the summary guidelines for healthcare professionals offer a much more manageable information source, and NICE have gone to extraordinary lengths to make these guidelines accessible to a very wide audience, including the public. NICE have also issued guidance on how to try to implement guidelines into practice. Thus, on face value, NICE guideline 43 is extremely relevant and potentially useful in the fight against obesity from a public health and primary care perspective.
However, reading the full guidelines plus the evidence summaries that underpin them reveals some interesting facts. In terms of reducing energy intake (dietary manipulation) the recommendations are based on findings from 29 studies, but only two of these were conducted in the UK with the majority being carried out in the US. Similarly, for behaviour change, only two studies were conducted in the UK, and the majority were carried out in the US. The evidence on exercise was derived from 33 studies, 26 of which were based in the US, and none in the UK. Although one could argue that the first law of thermodynamics and the energy balance equation applies to all people irrespective of nationality, there are of course cultural differences between countries that may influence the outcomes of different interventions in different settings.
Perhaps more importantly, very few studies cited in NICE guideline 43 were actually conducted in primary care (two on diet, one on behaviour change, and two on exercise) and most studies were conducted on volunteers (presumably with high motivation to lose weight). As NICE guideline 43 concludes:
‘It is difficult, therefore, to know how generalisable the results of the included studies are to the UK population, particularly in primary care. One assumption could be that the effect size achieved in the included studies may be smaller in practice.’
NICE also adds:
‘The effectiveness of all interventions appears to change over time, with a trend for greater weight loss in the short term (up to 12 months), with a reduction in overall weight loss in the longer term (up to 60 months).’ [Evidence Grade 1++].
Given that the NICE guidelines are developed for the UK healthcare system, and a key stated aim of NICE guideline 43 is to improve weight management in primary care (Box 1), one could question the relevance of many of the studies used to develop the guidelines to UK general practice and primary care.
Possible ways forward and future research
Numerous studies have shown the problems of implementing guidelines in general practice and primary care, and there is no need to re-state this except to highlight a few key points. The most commonly reported barriers to effective treatment in the primary care setting14 include:
psychological complexities of cases;
high rate of relapse;
perceived lack of effective interventions;
lack of time;
lack of resources; and
lack of onward referral options.
A qualitative study carried out on GPs and practice nurses in Scotland found similar barriers and concluded that:
‘A comprehensive and integrative primary care-led approach to weight management may be possible but will need substantial shifts of resources, organisation, training, and attitudes in order to maximise its potential impact.’15
In this issue of the Journal, Turner and colleagues report similar views from primary care practitioners in terms of childhood obesity.16 Also in this issue, Winzenberg and colleagues report that, rather than assessing physical exercise in all patients, GPs vary their approach depending on the clinical and social context.17 This is perhaps unsurprising given that many patients with obesity have other comorbid long-term conditions (related or unrelated to obesity). In a recent UK primary care study, 74% of obese patients had one or more comorbid conditions, almost half had two or more, and weight loss was less in those with comorbidities such as diabetes and arthritis.18 One way forward could be the recognition that the management of a complex condition such as obesity requires complex interventions.19 Given that evidence-based guidelines are based on studies that largely exclude patients with multiple morbidity, the management of obesity may benefit from studies specifically targeted at patients with multimorbidity.20–23
Obesity is socially patterned, with higher levels of obesity (with more multimorbidity) in areas of high socioeconomic deprivation, but with services that do not match need.24 There is a dearth of research on obesity management in deprived areas, or on specific interventions for people of differing socioeconomic status. In one study quoted in NICE guideline 43, a subgroup analysis found that a low-carbohydrate/low-fibre diet tended to be more successful for weight loss among people in a lower social class (classes III–IV) than a higher-carbohydrate/higher-fibre diet.25 Clearly, more targeted research may be helpful, especially given recent evidence suggesting effectiveness of low carbohydrate diets.25–27
Social interventions aimed at tackling obesity also offer an alternative interesting approach.28 Evidence from interventions in ‘real life’ primary care are also much needed and approaches such as ‘Counterweight’ in the UK are being watched with interest.18
In conclusion, obesity management is influenced by a huge range of human, system, and environmental factors. As NICE guideline 43 states:
‘It is unlikely that the problem of obesity can be addressed through primary care management alone … the clinical management of obesity cannot be viewed in isolation from the environment in which people live.’
Tackling the social determinants of health and the obesogenic environment must be top priorities. However, primary care clearly has an important role to play, but in such a complex condition as obesity, clinical guidelines alone cannot lead patient and practitioner through the labyrinth of decisions that need to be made in prioritising and targeting which problem to address first and how. Individualised care, clinical wisdom, and decisions based on a trusting relationship can, however, perhaps begin to tackle such complexity,29 and the traditional holistic strengths of general practice in the UK — population coverage and contact, relational continuity and empathic relationships, and an ability to deal with complexity30 — may offer part of the solution if the additional resources and support required are made available.
