The role of physical activity in obesity: let's actively manage obesity

Definitions

Physical activity: as any bodily movement produced by skeletal muscles that requires energy expenditure.⁹

Obesity: overweight and obesity are defined as abnormal or excessive fat accumulation that presents a risk to health. A body mass index (BMI) over 25 kg/m² is considered overweight, and over 30 kg/m² is obese.¹⁰ Caution is required when interpreting BMI, with consideration given to muscle mass, ethnicity, age and central adiposity.

Sedentary behaviour: defined as any waking behaviour characterised by an energy expenditure of ≤1.5 METs, while in a sitting, reclining or lying position.⁴

The benefits of physical activity and reducing sedentary time in obesity

The benefits of increasing physical activity and reducing sedentary time for individuals are wide reaching and well established. The UK Chief Medical Officers (CMOs) provide guidelines of the recommended minimum amounts of weekly physical activity (Fig 1).⁸

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Fig 1.

UK chief medical officers' (CMOs') physical activity guidelines for adults and older adults.

The use of BMI as a practical tool to define obesity has resulted in a focus on weight when assessing the success of physical activity programmes. Physical activity alone has a small but favourable effect on weight loss and overall fat percentage reduction for individuals with obesity. When considering exercise alone for weight loss in individuals with obesity, aerobic exercise and high intensity-interval training (HIIT) are preferable, although it is not possible to recommend one modality over the other.¹¹ The duration and intensity of the activity appear to be the most important factors of success.^12,13 Diet together with exercise appears to be more effective in inducing body compositional changes compared with either exercise or diet alone.^14,15 Ultimately, the most successful weight loss and weight maintenance programmes incorporate physical activity alongside other interventions where appropriate, as demonstrated in a summary of 48 studies, including 30 randomised control trials (RCTs).¹⁶

The role of GLP-1 analogues in assisting individuals with obesity to achieve weight loss is important. Unfortunately, much reporting of this has omitted that these medications are part of the toolkit rather than a singular solution. A strategy combining exercise (predominantly vigorous intensity cycling and running) and liraglutide therapy improved healthy weight loss maintenance more than either treatment alone.¹⁷ In fact, this combined strategy reduced the body weight and body-fat percentage approximately twice as much as the single-treatment strategies did. This was also associated with additional health benefits, including improved cardiorespiratory fitness and physical functioning.

Improvements in cardiorespiratory fitness and physical functioning can be achieved by a variety of exercise modalities. Aerobic, resistance, combined aerobic and resistance and HIIT increase VO₂ max, with HIIT having a slightly larger effect.^18,19 Resistance training improves muscle strength, with higher intensities conferring a greater effect. Limited evidence has shown that resistance combined with aerobic training improves other aspects of physical fitness profile, such as flexibility, balance and walking speed. Despite this, it has been demonstrated that exercise programmes improve quality of life for individuals with obesity. The challenge is that these outcomes are often not reported in trials, or at most included as a secondary outcome. A large systematic review, including 56 trials, investigated the impact of lifestyle and physical activity interventions on quality of life in obese individuals.²⁰ Only two of the included trials formally measured quality of life outcomes, but did show improvement in physical function and multiple other quality of life indicators at short-term follow-up.

Resistance training has been demonstrated to be effective at increasing fat-free mass in patients who are overweight or obese and this effect might also be present in older individuals.^14,21 This is particularly effective when the resistance training is progressive in nature, a process where the exercise prescription is altered to maintain or advance specific training goals and to avoid overtraining.²² The effect is less clear when resistance activity is pooled with aerobic exercise, because no significant difference in muscle mass was found. Aerobic training alone can induce loss of lean body mass and high-load resistance training might attenuate this, particularly when individuals are in a caloric deficit.^14,23 A similar affect for resistance exercise in reducing loss of femoral neck bone mineral density (BMD) during diet-induced weight loss has been observed. There was the suggestion on subgroup analysis that these findings are limited to patients aged >60 years of age.^24,25 Therefore, it is likely that a successful exercise programme might require both resistance and aerobic exercise modalities.

Cardiovascular disease is a specific concern for individuals with obesity and particular focus is given to risk factors in the research and clinical setting. Numerous studies have demonstrated the role of physical activity in the improvement of blood pressure,²⁶ lipid profile²⁷ and insulin resistance^25,28 in individuals with obesity. Those with the greatest derangement in these risk factors appear to have the most dramatic improvement. In terms of exercise type, aerobic training has many well-known benefits on cardiometabolic health and was the most frequent type of exercise assessed in studies. However, broadly speaking, no one exercise type can be conclusively deemed beneficial on risk factor reduction compared with others.²⁵ Obese individuals with higher physical activity levels and/or physical fitness have a lower all-cause mortality, highlighting the important role of physical activity in reducing cardiovascular disease.²⁹

Obesity can have a negative impact on the psychological health of individuals, and associations have been found between obesity and anxiety, depression, somatoform disorders and poor quality of life.^30–33 Numerous meta-analyses have shown that exercise is linked to lower levels of depression and anxiety, and improved quality of life in the general population.^34–37 The current literature investigating these benefits specifically for individuals with obesity shows a trend of small positive psychological effects of exercise training on psychosocial outcomes in overweight or obese individuals.³⁸ A recent meta-analysis showed a non-significant effect of exercise on depression scores, with one study reporting positive effects of exercise on anxiety.³⁹

Epidemiology

The response between amount of physical activity and its benefits is nonlinear, with those who are inactive with the most to gain. As outlined in Fig 1, CMO guidelines recommend at least 150 min of moderate-to-vigorous physical activity (MVPA) or 75 min of vigorous physical activity (VPA) per week with muscle strengthening activities on 2 days per week. There is no minimum amount of physical activity required to achieve some health benefits (Fig 2). In addition, sedentary time in adults is associated with all-cause mortality, cancer risk and survivorship. In all groups, the relationships of sedentary behaviour and health occur independently of MVPA for some health outcomes.⁴⁰ The curvilinear dose–response relationship between physical activity and health outcomes suggests that the proportionately greatest benefits come from progressing from being inactive to achieving moderate levels of activity, which are still below the threshold of the guidelines. Threshold recommendations might appear as a barrier to many, particularly those starting from low levels of physical activity, and discourage them from seeking to become more active. This is particularly important to consider because individuals with obesity in the UK have higher rates of sedentary behaviour and are two to three times more likely to report low levels of physical activity compared with normal-weight adults.⁸ The authors analysing UK biobank data noted that the differences were greatest in the higher obesity classes.

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Fig 2.

Dose–response curve of physical activity and health benefits.⁸

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Fig 3.

Infographic benefits outweigh the risks: a consensus statement on the risks of physical activity for people living with long-term conditions.⁵⁵

An association with physical activity levels and deprivation has been well documented. Physical activity levels decrease as deprivation increases, from 73% active in the least deprived areas, to 57% in the most deprived areas.⁴¹ Significant differences in activity levels are seen among ethnic groups, with people that identified as White British most likely to be physically active (47.7%), and those that identified as Black (35.7%), Other (38.0%) or Asian (38.7%) least likely to be active.⁴¹ These inequalities are mirrored in obesity levels. There has been a significant increase in obesity in the most deprived communities in England in recent years, leading to a widening gap between the most and least deprived areas. The latest figures demonstrate that those who live in the most deprived areas in England have a prevalence of excess weight 14 percentage points higher compared with the least deprived areas. Furthermore, an educational difference is observed among people with no formal qualifications, who have rates of excess weight 12 percentage points higher than among people with level four qualifications or higher.⁴¹ A difference is seen among people with disabilities, with 12 percentage points higher than among those without disabilities, and an ethnic variation is observed, with people in Black ethnic groups having the highest rates of excess weight.

Differences in obesity and physical inactivity rates translate to worse health outcomes for people in more deprived areas and contribute to health inequalities. The reasons for lower levels of physical activity in more deprived areas are multifactorial, cutting across economic, social, geographic and cultural factors. There is an important, yet underdeveloped, role for integrated care systems and local place-based partnerships in coordinating action.

Interventions to promote of physical activity

There has been a considerable interest in the use of digital tools to increase physical activity, with recent work showing their ease of use and effectiveness in providing short-term benefits.^39–42 This approach fits within the long-term agenda for digital tools to support existing services in the NHS and more widely, and has been found to be cost effective for some services.^43–46 Digital tools might also be preferable to engaging with traditional services for some, given the flexibility of accessing support at a time that suits them, reducing transport-related issues.

A recent review looking at digital tools to promote physical activity for obesity identified six studies; most delivered via web browsers and four used wearable devices.⁴⁷ The review concluded that there was a clear gap in the availability of digital tools, a lack of longer term follow-up data and questions of effectiveness. Earlier reviews reported positive but often small effects with considerable variability, and revealed that interventions providing stress management and communication skills (used in few interventions) and using a greater number of behaviour change techniques, had larger effects on health-related behaviours.^48,49

Another aspect that has received attention is the use of artificial intelligence (AI) to support behaviour change. Recent published work explored the use of chat bots or coaches, which could provide personalised recommendations, motivational messages, gamification and emotional support.⁵⁰ Several products, including MyFitnessPal, Lose It!, Noom and HealthifyMe, have had commercial success. Such products quantify hard-to-track behaviours, generate awareness and mindfulness about individuals' food and exercise-related choices, build accountability for actions and motivate toward achieving their weight loss goals. An ahead-of-print publication appears to suggest that greater success for weight loss is seen with human coaches + AI as opposed to AI alone. The analysis of the daily tracking data of 64,688 consumers over 3 years showed that, on average, human + AI coach plans lose 2.12 kg over 3 months, whereas those on the AI alone lose ∼1.22 kg in the same time frame.

Face-to-face behaviour change techniques have demonstrated improvement in physical activity rates.⁴² Techniques using motivational interviewing prompting behavioural practice or rehearsal might lead to better outcomes.⁵¹ Healthcare professionals are uniquely placed in efforts to combat physical inactivity because of contact with inactive people living with long-term conditions who are receptive to health advice from a trusted healthcare provider. A review of the integration of physical activity promotion within primary and secondary care settings identified a key barrier was having the confidence to raise the issue with the patient and to implement changes in their care.⁵² Resources, such as Moving Medicine, styled as the ultimate resource to help healthcare professionals integrate physical activity conversations into routine clinical care, provides evidence-based conversation guides for specific conditions.⁵³

Moving Medicine is one example of work coordinated on a national scale by SEM consultants to enable healthcare professionals to embed physical activity into treatment pathways. Clusters of NHS patients across community and secondary care have benefited from SEM expertise for 15 years and, where they do exist, they are highly regarded and expanding. Work at a system level has provided locally competent microsites joining up healthcare and sports partnerships. This has developed into the Active Hospitals Programme; a multicomponent intervention in which each pathway has a protocol to suit the varying physical and cultural environments, each with the aim of increasing in-hospital and postdischarge physical activity levels.⁵⁴ Following a successful feasibility and acceptability testing at Oxford University Hospital Foundation Trust, the programme has expanded to multiple sites, with varied work streams and an expanded community of practice.

Case example

At the end of a clinic appointment, a patient asks you whether he can exercise because of his weight. He is a 56-year-old male taxi driver with a BMI of 32 and no medical history of note.

Summary

• Physical activity, both in the form of aerobic and resistance training, has an important role in the management of obesity.

• There are numerous additional health benefits with physical activity outside of weight loss, which include improvement in cardiovascular fitness, mental wellbeing and bone mineral density.

• There is a curvilinear dose–response relationship between physical activity and health, suggesting that, proportionately, the greatest health benefits are seen in those who go from being inactive to moderately active.

• Interventions to help promote physical activity have increased enormously over the past decade, including motivational interviewing, mobile applications and AI.

• Sport and exercise medicine as a specialty can have a key role in the MDT for patients seeking to better manage their weight and improve their overall health.