Adult obesity management in New Zealand general practice: a review

KEYwords: Weight loss; obesity intervention; health-care professionals; primary care; obesity health care.

Obesity is an important health issue with New Zealand having the third highest obesity rate globally, behind America and Mexico.¹ Currently, 32% of New Zealand adults are classed as obese.¹ The most at-risk populations nationally are adults living in high deprivation areas and of Māori or Pasifika descent.² Obesity is a risk factor for several other conditions, including type 2 diabetes, cardiovascular disease, cancer and reproductive abnormalities.¹ Obesity is a socially discriminated health issue and correlates with psychological disorders such as depression, anxiety, social isolation and identity changes.^3–6 Obesity can also cause poor mobility, often because of joint strain, and collectively, these comorbidities can lead to loss of employment and an overall lower quality of life.^7–9 The health-care costs attributable to obesity and excess weight in New Zealand were estimated to be NZ$624 million in 2006 with this figure expected to increase.¹⁰ High rates of obesity and related comorbidities are causing economic strain on the health system through increased costs of time, resources, health-care demand, and loss of productivity.^10–12 Obesity reduction measures are urgently required.

Reducing obesity rates is achieved through effective weight management intervention and prevention strategies.¹³ The Ministry of Health’s Clinical Weight Management Guidelines for adults¹⁴ align with encouraged international approaches^15–18 which suggest that primary care professionals are best positioned to measure, monitor, advise, and intervene with their patients’ obesity risk.^14,17 The Ministry of Health advise that effective weight management is achieved through a combination of food control, increased physical activity and behavioural changes actioned in culturally appropriate ways,¹⁴ but there are multiple psychosocial, cultural, environmental and economic factors that influence the effectiveness of weight loss attempts.^19–21 Although there are many options for people to attempt to autonomously manage their weight outside primary care (using commercial weight loss programmes such as Weight Watchers and Jenny Craig, self-determined low-calorie diets such as Ketogenic or Optifast meal replacements, available over-the-counter meals, increasing exercise, or self-funded medication), primary care has been tasked with the job of delivering care for people living with obesity.¹⁴ Weight is related to many other health issues that primary care professionals treat (such as diabetes) and therefore is an integral part of primary care, yet little is known about how best to deliver this care. Regardless of how individuals engage with weight management, obesity is a complex health issue¹³ and there is minimal information about effective primary care weight loss interventions, or best practice approaches, for the unique New Zealand population.

Quality overseas reviews suggest that a combination approach of health-care professional counselling, meal replacements, commercial weight loss programmes or pharmacotherapy provides effective intervention.^22–25 The purpose of this review is to identify the range of interventions tested for use in New Zealand general practice, and to report on the effectiveness of these studies. This review aims to identify knowledge gaps, evaluate the research, and shed light on a significant health issue facing individuals, families and their primary health-care providers.

This review was based on the protocol detailed in the Cochrane Collaboration handbook for systematic reviews for interventions.²⁶ Due to the complex nature of obesity as a health risk, a stigmatised health condition, and a major public health issue, a review synthesis of quantitative literature was adapted to generate a comprehensive understanding of what is known about the management of obesity in primary care in New Zealand. Obesity was defined in this review as the clinical measurement of body mass index (BMI) >30, and BMI >25 for people with comorbidities.²⁷

Inclusion criteria were: original research, focused on weight loss intervention in general practice, published in English language, with a New Zealand adult sample aged 25–64 years who had a BMI >30 (or >25 BMI for participants with obesity-related comorbidities); and weight loss (kg) as a measurable primary or secondary outcome. Evaluations of weight loss programmes and interventions that also aimed to reduce comorbidities, such as HbA1c levels for diabetes, were included if weight change was also measured.

Excluded were: studies based on institutionalised participants, people with mental illness, cancer or pregnant participants, post-menopausal women only, and older (aged >65 years) adults only; family, child or adolescent-focused interventions; community-based or secondary care interventions with no involvement of primary health care; research where weight measurement was not an outcome; digital or web-only interventions; protocols.

The primary outcome measure was difference in bodyweight (kg) at baseline and after an intervention. Bodyweight could be measured by health-care professionals or self-reported. Studies were categorised into short (<12 months) and long-term (≥12 months): length of time interventions varied within each group.

In September 2020, we searched six major electronic databases for peer-reviewed papers published between 2000 and 2020: Scopus, PubMed, Web of Science, Cochrane Reviews, APA Psych Net, and AlterNative. Keywords used in the search strategy were variations of ‘food’, ‘weight’, ‘diet’, ‘weight loss’, ‘general practice’, ‘primary care’, ‘general practitioner’, ‘obesity’, ‘overweight’, ‘BMI’, ‘New Zealand’, and ‘nurse’. The AlterNative journal was included to elucidate quality research, give voice to minority groups, and generate a comprehensive review.

A total of 198 studies were retrieved and screened against the inclusion criteria, resulting in 22 full-text articles. From these, 11 were identified for inclusion in this review (Table 1).^28–38 The PRISMA flowchart in Figure 1³⁹ shows the selection process. Table 1 summarises the characteristics of the included studies. Table 2 summarises the intervention type, weight loss outcome and significance of results. Nine studies were found to have statistically significant weight loss from baseline, and two studies found no significant weight loss from baseline.

Table 1.  General characteristics and results of included studies

Figure 1.  PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2009 flowchart showing selection of articles.

Table 2.  Summarised results from included studies

Nine interventions produced statistically significant weight loss within their intervention timeframes. Two studies included a change in diet only,^32,36 one used diet changes and social support,³¹ one used diet and exercise changes,³⁵ one used exercise and behavioural changes,²⁸ three Māori approaches used exercise^34,37,38 and one included a Māori approach with behavioural changes, food education and exercise.²⁹

Interventions that included more than one weight management component (food, exercise, behavioural changes and culturally appropriate changes) all produced statistically significant weight loss results. The only interventions with an isolated component for weight loss that produced significant results was the changes in diet.^32,36

For Māori, in addition to the exercise, nutrition workshops and behavioural changes,^34,37,38 there was a strong cultural component,²⁹ which contributed to the statistically significant weight loss each intervention produced. The inclusion of whānau^29,38 and values such as whanaungatanga (support or connectedness),³⁷ pātaka mātauranga (sharing knowledge that leads to understanding and responsibility) and manaakitanga (enhancing the integrity of the person)³⁴ was integral to the weight loss achievements within these interventions.

Of the included studies in this review, four were randomised controlled trials (RCTs), three were cohort designs, one used convergent mixed methods, and three were Kaupapa Māori research. Six of the 11 studies included a diabetes component to their research. Weight loss ranged from no mean change³³ to 10.6 kg mean change.³² Intervention timeframes and weight loss measurements from baseline ranged from 9 weeks to 12 months. Three studies were long-term (measurements taken at baseline and at ≥12 months) and seven were short-term (<12 months).

Six of the 11 studies included a diabetes sample or focus and all produced significant weight loss. Three studies focused solely on patients with diabetes,^29,34,36 one on patients with prediabetes,³¹ and two with aims to reduce diabetes or heart disease in their study groups.^32,35

A survey found that the odds of losing weight were higher if patients changed both diet and exercise behaviours (17.5), as opposed to only physical activity (5.2) or only diet (7.2), and culturally appropriate interventions are vital for Māori and Pasifika populations.⁴⁰ No study included all three (or four for specific culturally tailored interventions) components in their weight loss interventions.

Two studies did not produce statistically significant weight loss within their intervention timeframes; one RCT used a medication-only intervention³⁰ and one cohort study used lifestyle behaviour changes only.³³ Neither study included a diabetes factor in their design.

This review of weight loss interventions in primary care among New Zealand adults identified only 11 studies, with heterogeneous study methodologies and mixed results. This review found that there are effective weight loss interventions available for patients in the primary care context, but they vary in strategy and suitability for individual patients. The intervention options tested align with the Ministry of Health best practice recommendations and included unique combinations of diet, exercise, and behavioural changes in culturally appropriate ways.¹⁴ Although the interventions did produce weight loss, the results ranged widely from 0.56 kg to 12.1 kg with variable follow-up times, leading to uncertainty that the findings are sustainable. These findings suggest that more comprehensive approaches are needed that include a combination of diet, exercise, and behaviour modifications conducted in culturally appropriate ways.

It was unsurprising to find that six of the studies in this review recruited patients with a diabetes diagnosis (an obesity comorbidity), as weight loss can reduce comorbidity risks.⁴¹ The weight loss results from these studies varied considerably (1.3 kg³¹ to 12.1 kg³²), highlighting difficulties in achieving weight loss while also controlling blood sugar levels. Weight gain prevention (and therefore diabetes prevention) could be more effective as an intervention due to the more achievable nature of weight management at a less severe obesity level.

When investigating the management and referral of obesity health care in a general practice, one study found that although obesity risk factors were managed appropriately by the general practice (following Ministry of Health guidelines), earlier identification and referral of high-risk patients could improve obesity health outcomes and act as an obesity prevention tactic.⁴² Effective interventions producing greater weight loss results could be better positioned at the time of a patient’s excess weight gain or identification of a high health risk, but before developing a comorbidity. This could enable individuals to reach weight loss and health goals faster and reduce additional health system strain. Further research is needed to determine the effectiveness of prevention as intervention for obesity and comorbidities at early stages of patients’ health journeys.

The low number and limited scope of New Zealand studies found for this review is surprising given the high obesity rates in this country,² and suggests that there are barriers to weight loss management in primary care. Obesity is a complex social, environmental, cultural and psychological health issue that also carries stigma and discrimination.^1,19,21,43 Previous studies have identified barriers to primary care obesity management, including ineffective conversational strategies, patients’ readiness to change, system limitations and inconsistencies in the general practice role in obesity management.^44–47

Some patients have beliefs that align with pro-obesity, believe that obesity is not a health concern for them or are unaware they are classified as obese, so do not seek obesity care.^48,49 These opposing views make obesity management a delicate and complicated issue for health professionals to deal with in their practice, as obesity is a significant issue both within and outside general practice. One study identified barriers to be lack of accessibility to effective interventions for their patients (including culturally appropriate interventions), stigma associated with obesity, and a lack of training, support or resources to support best practice obesity care.⁴⁵ These barriers could help explain failures to reduce obesity rates in recent years. Further investigation is needed to identify and mitigate barriers to obesity health care and generate support for primary care professionals who are tasked with providing this care effectively.

Primary care professionals are positioned as responsible for intervening in obesity care,¹⁴ yet there is limited information available to inform ‘best practice’ for this individualised and complex health issue. Overseas research has found that medications,²⁴ very low energy diets and meal replacements,^50–52 commercial weight loss programmes,^25,53 and dietitian referral⁵⁴ interventions produce positive weight loss outcomes, and they also support multileveled intervention approaches.^22,55 Primary health-care professionals can refer to previous New Zealand research that focuses on children, adolescents, older adults or secondary care,^56–59 but research does not directly assist with health-care professionals’ best practice options for patients outside these samples. Culturally appropriate interventions for high-risk populations, including Māori and Pasifika, have also been tested, but these interventions are actioned at the community or family level rather than in primary care.^60,61 Another recent study used a partnership methodology of an academic university team and a Māori community health provider who co-designed a lifestyle intervention programme with Māori men and community stakeholders and was not based in a general practice (or clinical) context.⁶²

Until more definitive New Zealand research is completed, it is reasonable for health professionals to use a combination of weight loss evidence from international samples, New Zealand-based evidence, and Ministry of Health guidelines¹⁴ to guide their practice. Using this available literature is recommended in conjunction with medical advice and tailoring to specific patient needs (including medical, cultural and psychosocial needs) for effective obesity health-care delivery.

This review is subject to publication bias and time lag. Further limitations were the inclusion of English-language articles only, exclusion of grey literature and hospital-based research, along with interventions that had no weight loss outcome measurement. General methodological problems, including participant dropout rates, participants’ compliance with interventions, and self-report bias, could skew the reported effectiveness of these interventions. The statistically significant weight loss found in 9 out of 11 studies was measured to the timeframe of each study and not checked beyond this for sustainability of effectiveness. Furthermore, diabetes intervention research was not purposely searched for, but due to the integrated nature of diabetes and obesity, some diabetes studies with weight loss measurements appeared from the searches. Although including diabetes-specific research could generate more studies, the aim of this review was to understand primary care interventions about all adults, including those without comorbidities.

In conclusion, the current evidence of effective primary care weight loss interventions in New Zealand is limited and based on a low number of studies. Nine out of the 11 studies identified achieved significant weight loss from their interventions, showing promise, although weight loss was not measured long-term for sustainability. The Kaupapa Māori studies achieved similarly significant weight loss results, demonstrating that the inclusion of a cultural component is effective and important for Māori people. The current literature is too sparse to allow for firm conclusions to be drawn as there is too much heterogeneity in participant populations, theoretical perspectives, and study designs. Primary care clinicians should draw upon the combination approach of dietary, exercise, and behavioural changes for effective obesity interventions in their practice. Until more research is done in New Zealand, primary care professionals may use international evidence for effective weight loss interventions, while offering tailored health advice that takes into account the medical, cultural and psychosocial needs of individual patients. Further research is needed to identify barriers influencing the effectiveness of primary care obesity interventions in New Zealand to improve health outcomes and reduce the burden of obesity on the health system.

This project was part of a larger PhD project for Kimberley Norman (University of Waikato), which is funded by the Waikato District Health Board Research Trust.

The authors declare no competing interests.