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Obesity in adults is an important risk factor for a number of chronic conditions, including hypertension, coronary heart disease, stroke, type 2 diabetes and some cancers. Furthermore, it is directly related to increased mortality and lower life expectancy.
In May 2017, the World Obesity Federation published a Position Statement declaring that obesity is a chronic, relapsing, progressive disease process (Bray et al, 2017). This adds to the weight of opinion from other authorities, including the World Health Organization (WHO, 2000), the American Medical Association and the Canadian Medical Association, that define obesity as a disease, whether or not it is a social problem as well.
As the prevalence of obesity increases, it is expected that the associated medical problems will also increase.
In 2015, 27% of the adult population in England were classified as obese, with a BMI >30 kg/m2 (NHS Digital, 2017). In total, 58% of women and 68% of men were classified as either overweight (BMI 25–30 kg/m2) or obese. This suggests that the majority of the population, and the people who are seen in primary care on a daily basis, are more likely to have a weight problem than be of a healthy weight. The prevalence of morbid obesity (BMI >40 kg/m2) has reached 2% of men and 4% of women, triple that observed in 1993. If current trends continue, by 2050 nine out of every 10 adults will be overweight or obese, and 50% will be classified as obese by BMI (Butland et al, 2007).
More than calories in, calories out?
Genetic factors have long been recognised to be associated with obesity. However, it is only recently that investigators have learnt how the key gene, FTO (fat mass and obesity-associated protein), actually works. A faulty version of FTO causes energy from food to be stored as fat rather than burned (Claussnitzer et al, 2015). However, the genetics of obesity should not be a distraction to effective management. A recent study concluded that genetic predisposition to obesity associated with the FTO minor allele can be at least partly counteracted through diet, physical activity and drugs (Livingstone et al, 2016).
For some time now, short sleep duration has been associated with gut and brain hormone changes associated with increasing risk of obesity (Taheri et al, 2004). Further studies since then have shown similar effects in childhood, stressing the importance of regular bedtimes and sufficient sleep duration and quality. However, more recently, there has been research showing that any “abnormal” sleep – either too much or too little – can be linked with obesity in those with a genetic predisposition (Celis-Moralis et al, 2017).
Recent developments in our knowledge of the gut microbiome and its effects on metabolism in humans have arguably raised more questions than answers (Munro, 2016). Further research into this field may provide important new strategies for the management of obesity and diabetes, but at present this is outside of the scope of this article.
Defining obesity and identifying risk
If a person expresses an interest in adopting a healthy lifestyle and losing weight, the first step should be to measure height, weight and waist circumference to establish whether he or she currently has a problem relating to weight and degree of risk.
Body mass index
The WHO (2000) has standardised the definitions of weight and obesity with its well-established classification based on BMI (Table 1). However, on the individual level, BMI can be inaccurate, with particularly muscular people being classified as obese when, in fact, they are healthy with no significant risk of cardiometabolic conditions. BMI measurements should, therefore, be supplemented by measurements of waist circumference.
There is a strong correlation between increasing waist circumference and levels of central, or visceral, fat (as distinct from subcutaneous fat), which is deposited in and around central organs and increases cardiometabolic risk (Pischon et al, 2008). For every 5-cm increase in waist circumference, there is a 17% increased relative risk of death for men and 13% for women, independent of BMI (Pischon et al, 2008). However, analyses of prospective studies suggest that the “pear” shape may not convey any lower risk than the “apple” shape, which implies that waist circumference should supplement, but not replace, other indicators of risk (Emerging Risk Factors Collaboration, 2011; Huxley and Jacobs, 2011).
Central obesity in the Caucasian population is defined as a waist circumference of ≥94 cm in men and ≥80 cm in women (NICE, 2014). Further details on waist circumference are presented in the first version of this module (Capehorn, 2011; available at: https://is.gd/capehorn).
The best assessment of a healthy weight in the Caucasian population is a BMI of 18.5–25.0 kg/m2, and a waist circumference of ≤80 cm in women and ≤94 cm in men. As Hill (2013) has observed, however, the “evidence to give specific cut-points for BMI and waist circumference for individual ethnic minority groups is still not available.” For the time being, NICE (2013) recommends that 23 kg/m2 can be applied as a BMI cut-off point for high risk in ethnic minority groups.
Consequences of obesity
Obesity in adults is an important risk factor for a number of chronic conditions, including hypertension, coronary heart disease, stroke, type 2 diabetes and some cancers (Kopelman, 2007). Furthermore, it is directly related to increased mortality and lower life expectancy (Lee et al, 1993; Adams et al, 2006).
Obesity increases the risk of developing type 2 diabetes by 12.7 times in women and by 5.2 times in men (National Audit Office, 2001). Adipose tissue is now established as a highly metabolically active organ, and its link to the development of insulin resistance, inflammatory markers and dyslipidaemia is becoming clearer. Excess fatty acids and the adipocytokines released by adipose tissue impair the action of insulin. Visceral fat causes low-grade inflammation, with oxidative stress – in particular pancreatic beta-cell stress – leading to further insulin resistance. A cycle then develops, with further beta-cell dysfunction resulting in excess glucose production, impaired glucose uptake and utilisation and, ultimately, further insulin resistance, impairment of glucose homeostasis and the development of type 2 diabetes (Brewster, 2008). One way to break this cycle is to prevent the development of the central adiposity.
Recent fresh evidence has also linked adiposity with multiple different cancers (Kyrgiou et al, 2017). Obesity is most strongly associated with oesophageal adenocarcinoma, multiple myeloma, and cancers of the gastric cardia, colon, rectum, biliary tract system, pancreas, breast, endometrium, ovary and kidney.
An obesity paradox?
Over the years, many have questioned whether the “obesity paradox”, whereby low-grade obesity appears to be beneficial in certain people, is a real phenomenon. However, in 2017, a large study of 22 5000 people was published that disputes this theory and adds more conclusive evidence that, without exception, adults who become overweight or obese have a higher risk of dying from heart disease, cancer or other illnesses (Yu et al, 2017).The authors used 16-year weight history, rather than a single baseline measurement, and observed an increased risk of death from any cause in all groups of excess weight, even those with a BMI of 25.0–29.9 kg/m2.
The highest risk of death occurred in participants who had substantial decreases in weight, which most likely reflected unintentional weight loss from disease and complications (Yu et al, 2017). This may explain the J-shaped curves observed in other studies. Morbidly obese participants were twice as likely to die from any cause, more than three times as likely to die from heart disease and 50% more likely to die from cancer when compared with normal-weight individuals.
Management of obesity
Comprehensive guidance on the prevention and management of overweight and obesity in adults and children was published by NICE in 2006. This guideline (CG43) has since been partially updated to CG189 (NICE, 2014), which adds guidance on bariatric surgery and very-low-calorie diets (VLCDs). Individuals should ideally be managed by a multidisciplinary team (MDT).
It is important to appreciate that obesity is a chronic, relapsing condition. Instead of focusing on managing the consequences of obesity, the causes should be tackled, and the person who is motivated to address any unhealthy weight issues should be appropriately managed.
Many people may feel uncomfortable about raising and discussing the issue of body weight; therefore, because it is such an important health concern, the clinician may be required to broach the subject. However, a 2015 review of 91 000 medical records where the GP had recorded excess weight found that 90% of obese patients were not documented to have been given lifestyle or dietary advice, referred to weight management services or offered anti-obesity drugs by their GP (Booth et al, 2015).
With regard to people with diabetes, the IntroDia study, which interviewed over 10 000 patients and nearly 7000 physicians regarding initial and subsequent conversations in diabetes, demonstrated that physician respondents in all of the 26 participating countries felt that good diabetes care was approximately 50% about the choice of drug and 50% about lifestyle/behaviour change (Capehorn et al, 2017). Physicians do not focus on the latter enough. In my opinion, encouraging people to make small, manageable changes to their lifestyle is likely to be more successful than attempts to radically alter their diet and physical activity.
Diets or healthy ways of eating should be tailored to the individual. To encourage adherence, clinicians should avoid dictating to people what food they should eat, and food preferences must be taken into account. For most people, avoiding unhealthy food options will improve weight loss efforts greatly.
Management should still start with looking for obvious problems, such as portion control; changing snacks to less calorie-dense options; lack of understanding of the effects of a “day off the diet”; and alcohol and high-calorie, low-fat foods. An understanding of calories is also important; this is covered in greater detail in the first version of this module (Capehorn, 2011).
A hypocaloric diet with a 500–600 kcal/day deficit below a person’s daily requirement (as predicted by the Harris–Benedict or Schofield equations [Box 1], or by the use of specialist equipment) or that reduces calories by lowering the fat content (low-fat diets) or total carbohydrate intake, in combination with support and follow-up, is recommended to promote sustainable weight loss (NICE, 2014).
A change in diet may have significant impact on the treatment regimen of a person with type 2 diabetes, especially when they are taking numerous medications (particularly oral medications or insulin regimens associated with a risk of hypoglycaemia). This will require careful consideration and perhaps an MDT approach involving the diabetes specialist nurse and the dietitian.
What is a healthy diet?
Questions continue to be raised over what macronutrients are most responsible for obesity, and indeed what constitutes a “healthy” balanced diet. There is debate among experts as to whether sugar has a greater responsibility than fat for the obesity epidemic, with sound clinical arguments on both sides (Taubes, 2013; Watts, 2013). A meta-analysis and systematic review of 72 studies (45 cohort studies and 27 controlled trials) demonstrated that, with the exception of trans fats, which were associated with increased coronary disease risk, there was no evidence to suggest that saturated fat increases the risk of coronary heart disease or that polyunsaturated fats have a cardioprotective effect (Chowdury et al, 2014). However, current UK guidelines with respect to fat intake remain unchanged (men should consume no more than 30 g of saturated fat per day, and women no more than 20 g per day; NHS Choices, 2017).
Clearly, further research is required to establish the optimal macronutrient composition of a healthy, balanced diet, but it should at least be remembered that fat is calorie-dense (9 kcal/g) and that eating too much of it without curbing calorie intake from other food groups will lead to obesity.
In contrast to fat, guidelines and Government policy do seem to be changing with respect to sugar. Both the WHO (2015) and the UK Scientific Advisory Committee on Nutrition (SACN, 2015) have made policy statements aiming to reduce the intake of, specifically, “free” sugars (i.e. those that are added to food, such as table sugar and glucose), to 10% of our total daily dietary intake of calories, with SACN aiming to reduce it further to just 5% (i.e. 25 g or six teaspoons per day).
More recently, a debate has been opened regarding the role of artificial sweeteners in the management or risk of obesity and diabetes. A recent Swedish study suggested that as little as two “diet” drinks per day could double the risk of developing type 2 diabetes and latent autoimmune diabetes in adults (LADA; Löfvenborg et al, 2016), and researchers have argued that regular consumption could actually increase the likelihood of weight gain (Borges et al, 2017). However, current opinion continues to support switching to sugar-free beverages to help with the management of obesity and diabetes; indeed, a very large systematic review and meta-analysis has concluded that low-calorie sweeteners help people to reduce energy intake and can be a useful tool in weight loss (Rogers et al, 2016).
In a recent review examining the role of dietary sugar in type 2 diabetes, the authors concluded that sugar consumption can lead to type 2 diabetes, but the risk is substantially reduced when adjusted for BMI (Lean and Te Morenga, 2016). Surprisingly, in people with type 2 diabetes, there was little evidence that sugar consumption aggravates glycaemia; however, it does promote macrovascular and, to a lesser degree, microvascular complications associated with the condition.
The media has not helped by publishing conflicting evidence from different organisations and researchers recommending different diets made up from different macronutrients. Owing to the conflicting information on fats and the recent trend against sugars, supporters of the low-carbohydrate diet have been promoting it as the preferred choice for weight loss (and in some cases type 2 diabetes). However, the evidence suggests that the macronutrient composition of the diet does not make a significant difference and that it is the total energy (i.e. calories) consumed that matters the most.
In 2012, a landmark systematic review and meta-analysis concluded that any changes in adiposity were mediated via changes in energy, not macronutrient composition, and the authors noted that substituting sugar with other carbohydrates of equal caloric value was not associated with weight change (Te Morenga et al, 2012). In a more recent meta-analysis, low-carbohydrate diets were compared with isoenergetic balanced diets for reducing weight and cardiovascular risk, and the conclusion very strongly showed that weight loss was unrelated to the macronutrient composition and was mostly only short-term, with little or no difference in weight loss or cardiovascular risk up to 2 years later (Naude et al, 2014).
With increasing evidence that weight management relates mostly to energy intake, starchy foods and other carbohydrates need to be considered in the same way as refined and other sugars. However, it is important to note that, while refined sugars are considered to have no nutritional value, starchy foods and other carbohydrates still form part of the dietary “Eatwell” Guidelines (Public Health England, 2016).
The use of very-low-calorie diets (VLCDs; also known as very-low-energy diets [VLEDs]), which comprise a caloric intake of 450–800 kcal/day, is supported by the National Obesity Forum (NOF, 2010) and NICE (2014), strictly as part of a multicomponent weight management strategy, for patients who are obese and who have a clinically assessed need to rapidly lose weight. The short-term use of a VLCD rapidly improves glycaemic control and promotes substantial weight loss in obese people with type 2 diabetes (Capstick et al, 1997).
There is an ongoing study, funded by Diabetes UK, titled DiRECT (Diabetes Remission Clinical Trial), which is examining the role of VLCDs in weight loss and their potential for diabetes remission (Leslie et al, 2016). Although the trial is not yet complete, looking at the provisional data, the investigators expect diabetes remission rates of 30–50% within the region of 15% weight loss, without the use of weight-loss medication.
The advantages of VLCDs include the rapid and significant weight loss which, if the VLCD is adhered to, results in weight loss comparable to that with bariatric surgery, without being invasive and without any subjective hunger once the patient becomes ketotic.
Recent research has outlined the benefits of rapid weight loss over the traditional “slow and steady” approach, as the rate of weight loss does not appear to affect the proportion of weight regained (Purcell et al, 2014; Rolland et al, 2014). This suggests the health benefits associated with weight loss can be achieved more quickly, and potentially for longer, with more rapid weight loss. In practice, there is still a common belief that a high rate of weight loss is not advantageous and will lead inevitably to weight regain, but this view is slowly being challenged (Johanssen et al, 2014; Christensen et al, 2017).
Meal replacements and total food replacement programmes represent alternative dieting options, and these are covered in the first version of this module (Capehorn, 2011). In my opinion, use of specific diets such as VLCDs will be more effective with full MDT support, and we may see use of this type of diet increasing over the next few years.
Although physical activity has proven cardiovascular health benefits and a role in maintaining weight loss, it is generally considered to be a less efficient intervention for actual weight loss than reducing caloric intake. The maxim that “you cannot outrun a bad diet” demonstrates this point (Malhotra et al, 2015). However, it is crucial to the maintenance of weight loss (Hill et al, 2005).
The WHO (2017) has updated its advice regarding physical activity, recommending that adults have at least 150 minutes of moderate-intensity activity per week. It stated that physically inactive people have a 20–30% increased risk of death compared with active people.
The current Government recommendation in England is for a minimum of 30 minutes of moderate-intensity physical activity on at least 5 days per week for general health; however, for weight loss or maintenance of reduced weight, physical activity should be increased to 60–90 minutes on at least 5 days per week (NICE, 2014). The level and type of physical activity will depend on what is achievable for the individual and should focus on what is acceptable within his or her normal lifestyle in order to improve adherence.
Being aware of the obesogenic environment in which we live may also be beneficial. Encouraging individuals to take the stairs instead of a lift or escalator, and parking further away from the entrance to the supermarket, for example, can be as beneficial as planned physical activity. More walking should be encouraged, especially for the short distances normally travelled by car, as should reducing sedentary behaviour such as watching television.
A meta-analysis performed in 2001 showed that exercise training reduces HbA1c levels by sufficient amounts to reduce the risk of diabetes complications, although the precise metabolic changes and effects attributable to the exercise are still not yet fully understood (Boulé et al, 2001). However, no significant difference in body mass was found when exercise groups were compared with control groups, and there was insufficient evidence to define any dose–response effect of acute exercise on glucose metabolism.
Behavioural therapy and “talking therapies”
Behavioural therapy strategies have varying levels of adherence and effectiveness, but include recording diet and exercise patterns in a diary, identifying and avoiding high-risk situations (such as having high-calorie foods in the house, or eating mid-morning snacks with work colleagues when not really hungry), and changing unrealistic goals and false beliefs about weight loss and body image to realistic and positive ones. When used in combination with other weight-loss approaches, behavioural therapy provides additional benefits in assisting people in losing weight (Shaw et al, 2005).
The collective term “talking therapies” includes life-coaching, cognitive behavioural therapy, neurolinguistic programming, emotional freedom techniques and hypnotherapy. Although there is not yet convincing evidence that these techniques offer equivalent effectiveness to that of other interventions (high-quality randomised controlled trials will be required to assess their true role), there is no doubt that some people with diabetes prefer these approaches, and treatment should be tailored to the individual.
Eating can be a strategy for coping with emotional distress (Nash, 2014) and such individuals need to be taught strategies for tackling their emotions, without using food for non-hunger-related reasons. Many people with severe and complex obesity who hope to undergo bariatric surgery have emotional eating issues and, unless addressed, their outcome is likely to be less successful (National Confidential Enquiry into Patient Outcome and Death, 2012). This is why the NHS Commissioning Board (2013) guidelines for bariatric surgery focus heavily on the need to include psychological assessments and support in all bariatric surgery candidates.
Pharmacotherapy should be considered as part of a comprehensive strategy of obesity management. There are now three licensed weight-loss medications in the UK. The most established is orlistat, a gastrointestinal lipase inhibitor that prevents absorption of around 30% of dietary fat. It is taken orally with meals and should be prescribed only as part of an overall plan for managing obesity in adults with a BMI ≥28.0 kg/m2 with associated risk factors, or a BMI of ≥30.0 kg/m2 (electronic Medicines Compendium, 2013). Factors related to prescribing orlistat are described in more detail in the first version of this module (Capehorn, 2011).
More recently, in 2017, two other medications were approved for obesity. Both can be considered as appetite suppressants. Saxenda® (liraglutide 3.0 mg) is a glucagon-like peptide-1 (GLP-1) receptor agonist that has been prescribed for the management of type 2 diabetes at doses of 1.2 mg or 1.8 mg. Weight loss is achieved mainly through inhibition of gastric emptying and through effects on the central nervous system that result in decreased calorie ingestion, as well as reducing acid secretion (Van Gaal and Scheen, 2015).
Mysimba® (a combination of sustained-release naltrexone and bupropion) increases levels of dopamine and pro-opiomelanocortin neuronal activity. Weight loss is achieved by suppressing appetite due to increased secretion of melanocortins, which mediate anorectic effects and regulate energy balance (Van Gaal and Scheen, 2015).
In August 2017, NICE rejected Mysimba for routine NHS use. No decision has yet been made on Saxenda.
A systematic review and meta-analysis of available weight-loss drugs in the US (including a phentermine/topiramate combination and lorcaserin, which are currently not available in the UK) demonstrated the effectiveness of the newer weight-loss medications (Khera et al, 2016). The results are summarised in Table 2. Compared with placebo, liraglutide and naltrexone/bupropion had the highest risk of treatment discontinuation related to adverse events. Other drug classes and combinations are in development for potential use in the future (Van Gaal and Scheen, 2015), but these are currently beyond of the scope of this article.
The efficacy of weight-loss pharmacotherapy should be evaluated after the first 3 months. In the case of Saxenda and Mysimba, this is recommended to be 3 months after reaching the full treatment dose (i.e. 3 months after a 4-week uptitration from the starting dose, which helps to avoid side effects). NICE (2014) suggests that the adult target for weight loss should be 5–10% of the original weight; however, obesity consensus guidelines conclude that a target loss of 5% is appropriate, although individualised targets may well be less (Barnett et al, 2009).
Diabetes treatment and weight
Many antidiabetes medications are associated with weight gain. Even drugs that are not directly associated with weight gain may indirectly contribute if they result in excess circulating insulin levels, as insulin promotes adipogenesis and weight gain (Kahn et al, 2006). NICE (2014) recommends metformin as first-line treatment for people with type 2 diabetes, providing there are no contraindications to its use, and studies have shown metformin to be weight-neutral (Nathan et al, 2009). However, sulfonylureas, thiazolidinediones, meglitinides and insulin have all been shown to promote weight gain.
There are newer classes of diabetes medications that are more weight-friendly and, although not licensed for weight loss, their use should be considered if weight is an issue. Dipeptidyl peptidase-4 inhibitors are weight-neutral, while GLP-1 receptor agonists and sodium–glucose cotransporter 2 inhibitors promote weight loss (Nathan et al, 2009; Munro et al, 2013; NICE, 2014).
The updated NICE guidelines on the management of type 2 diabetes in adults (NG28) allowed more flexibility to prescribe appropriate weight-friendly antidiabetes agents within the care pathway for people with diabetes who are also overweight or obese (NICE, 2015).
Bariatric surgery is a cost-effective clinical option for appropriate obese patients who have been properly managed and assessed for clinical and psychological barriers to effective weight loss (Picot et al, 2009). The success will be dependent on appropriate pre- and postoperative counselling provided within an MDT.
Roux-en-Y gastric bypass and sleeve gastrectomy require lifelong supplementation and monitoring postoperatively. This currently takes place in specialist services for the first 2 years and thereafter in primary care. Detailed information on referral and pre- and postoperative management is provided in an accompanying article in this Journal (Zalin et al, 2017).
Any change in diet that results in lower calorie consumption, whether due to reduced portion size or consuming foods that are less calorie-dense, will result in weight loss. However, it is common for weight loss to plateau, for several reasons. Ultimately, as weight decreases, so do energy requirements, and eventually calorie intake (at levels that were previously at a deficit) may become equal to energy requirements. Furthermore, an individual may drift back into bad habits and fall foul of the obesogenic environment. Where weight loss does not plateau, the diet will need to be adjusted again, once a healthy weight has been achieved, in favour of one that is nutritionally balanced and sustainable in the long term, with ability to make rapid adjustments if weight regain occurs.
Weight regain is complex and appears to be part of a homeostatic adaptation involving many different hormones. Even after a significant period of time following weight reduction, levels of these circulating mediators of appetite that encourage weight regain stay higher than before weight loss (Sumithran et al, 2011). Clearly, new therapies to tackle this hormonal regulation of body weight will be required to counteract this change if we hope to prevent relapse of obesity.
An MDT approach to weight management
NOF (2007) recommends that best-practice specialist weight management interventions be based on an MDT approach. This specialist tier of intervention for adults and children with weight problems should comprise a team of specialists that can deliver different approaches to weight loss. This will ideally include dedicated obesity specialist nurses (OSNs), healthcare assistants (HCAs), dietitian input for complex dietary needs, “Cook & Eat” programmes for cooking skills education, talking therapies providing psychological input and support, exercise therapists who can provide personalised training programmes, and a GP with a special interest in obesity for any medication issues. There should also be facilities for group work in relation to exercise, talking therapies and nutritional advice.
The specialist MDT service could also provide the triage and assessment for all people being considered for further interventions, which may include bariatric surgery in adults or the attendance at residential weight management camps for children.
As with all consultations, a good history and examination is vital. All people should initially have measurements of blood pressure, weight, height, BMI, waist circumference and, where possible, fat composition using bio-impedence scales. The use of bio-impedence measurements helps to dispel some of the myths that people have that they are “big-boned”, that it is “all muscle”, or “just fluid”. Furthermore, as individuals increase their level of physical activity and hopefully increase their lean muscle mass, bio-impedence measurements can demonstrate that, even in the absence of any actual overall weight loss, visceral fat may be decreasing and being replaced by muscle, which is more dense. However, an effective weight management clinic can be run with just a height measure, some accurate scales and a tape measure.
If no recent blood tests have been performed, these should be taken to exclude previously undiagnosed metabolic conditions, such as diabetes and non-diabetic hyperglycaemia, underactive thyroid or other associated risk factors. Standard blood tests in nearly all individuals should in
PCDS Chair, Clare Hambling, pays tribute to Pam Brown, winner of the 2022 PCDS Lifetime Achievement Award.
29 Mar 2023