Obesity is a chronic disease that affects more people in Ireland that any other. The disease of obesity is associated with several other diseases, such as type 2 diabetes, cardiovascular disease, and cancer. The morbidity associated with obesity is so significant that it limits life expectancy.
Terming obesity as a disease is sometimes controversial, as many understand it as a result of poor food choices and a sedentary lifestyle. While these factors can contribute to the development of obesity, there are multiple other factors involved in the pathogenesis of the disease of obesity, including genetic factors, and dysregulation of energy metabolism.
Blaming people with obesity for having obesity because at some point in their lives they ate high-calorie foods, is like blaming people with lung cancer for having cancer because at one point they smoked (even if that was over 20 years ago). The development of the disease of obesity is much more complex than ‘eating too much and doing too little exercise’.
Many of us who do not have obesity might reflect on our own diet and activity levels and find that we often eat high-calorie foods and do not often take a lot of exercise. In contrast, we might have patients, friends, or family living with obesity who are actively dieting and going for long walks every evening, but remain unable to lose significant amounts of weight and continue to have obesity despite years of trying to lose weight. The evidence for a biological basis for obesity is in the published literature, but it is also all around us in our daily lives.
The lack of understanding of the disease of obesity contributes to a phenomenon termed ‘obesity stigma’. We live in a society that feels free to openly discriminate against people based on their weight. People living with obesity are often portrayed as unmotivated (‘lazy’) and undisciplined (‘greedy’). The common narrative is that if people have obesity, then it is their fault, and that if they just became motivated and disciplined, then their obesity would resolve.
When we stigmatise people living with obesity as unmotivated, undisciplined people who do not take responsibility for their own health and wellbeing, it gives us license to blame them for their poor health, to criticise them for their life choices, and even to decline to employ them. It also allows us to rationalise a clinical approach that apportions all the responsibility on the patient and avoids offering proven clinical interventions that successfully treat the disease of obesity. Given the prevalence of obesity stigma, it is no surprise that obesity is associated with depression, anxiety, reduced social participation, and reduced quality-of-life.
Over the last three decades, repeated studies have shown that for the vast majority of people living with obesity (approximately 80 per cent), diet and exercise-based interventions do not result in long-term weight loss. This is not because of a lack of effort on their part. They continue to attend for often intensive research protocols over years, but despite doing so cannot maintain their weight loss. We now know that this is not because people with obesity are lazy and greedy: It is because of maladapted energy homeostasis and genetic predisposition, in concert
with multiple biological and external factors, resulting in the development of a disease called obesity.
Treatment of the disease
For the majority of people who attempt diet and exercise interventions to treat their obesity and lose weight, their physiology defends against weight loss. The first physiological defence mechanism is hunger. Reduction in food intake results in increased hunger. Like many primal reflexes and functions, hunger is unconscious. However, when people on a diet become hungry they can consciously resist their hunger in an effort to lose weight. This can result in some weight loss, but living in a constant state of perceived starvation is very challenging to maintain and requires constant conscious resistance of hunger.
If people do manage to constantly resist hunger and maintain a calorie deficit (ie, consume fewer calories than they expend) then the other major physiological adaptation that helps resist weight loss is activated: This is a reduction in the metabolic rate. This mechanism is why people will eventually reach a weight-loss plateau, despite sticking to a diet that initially resulted in weight loss, and continues to result in hunger. During a diet, the metabolism reacts as it would during a famine and energy expenditure is minimised to meet the reduced calorie intake. Therefore, people on a diet will continue to burn fewer calories as long as there is a calorie deficit.
The only way to overcome these mechanisms is to consciously reduce calorie intake to extremely low levels (approximately 600kcal per day), which is unhealthy to maintain and consistent with starvation. Even if someone can achieve this for a time, on reintroduction of normal diet with a calorie intake within recommended limits (eg, 2,000kcal per day) there will be weight regain as their healthy 2,000kcal a day diet will be in excess of what they are expending by the end of their diet (which could be lower than 1,000kcal per day).
Given these mechanisms, it is no surprise that for over 80 per cent of people with obesity, diet and exercise interventions alone will not achieve durable weight loss. Of course, this means that as many as 20 per cent of people with obesity will achieve significant weight loss in the long-term as a result of diet and exercise interventions and so a structured diet and exercise programme is a reasonable first-line treatment for obesity if the individual has not completed a structured intervention before.
Ideally, a structured diet and exercise programme would be provided in the public sector and be dietician and/or exercise physiologist-led, with psychologist support. If such a programme is not available then there are commercially available options. If such a programme is not available at all, then a relatively simple class-based programme can at least offer structured advice on calorie reduction and peer support.
Exercise is an important component of any weight loss programme not because it significantly aids weight loss, but because it helps weight maintenance and minimises the risk of weight regain. Regular exercise is shown to reduce weight regain after successful weight loss achieved with dietary modification. This exercise does not have to be gym-based or exercise therapist-led. Any additional exercise such as walking can be of benefit, but a minimum of 30 minutes a day is needed to gain this benefit.
When diet- and exercise-based programmes are unsuccessful, then medical therapy should be considered as next-line therapy. There are four medical options at present – orlistat, liraglutide (at a dose of 3mg daily rather than the 1.8mg dose used for diabetes), naltrexone/bupropion, and semaglutide (at a maximum dose of 2.4mg rather than the 1mg use in the treatment of diabetes). All of these can be prescribed safely in primary care although at the time of writing there are some supply issues with respect to semaglutide. For current prescribing information, please see www.medicines.ie and/or www.hpra.ie/homepage/medicines.
Ongoing obesity research is resulting in a greater range treatment options. Tirzepatide is a new medical therapy that can produce over 20 per cent weight loss, thus approximately the weight loss achieved with bariatric and metabolic surgery. This agent is a once-weekly GIP (glucose-dependent insulinotropic polypeptide) receptor and GLP-1 (glucagon-like peptide-1) receptor agonist that treats some of the fundamental physiological metabolic dysfunction inherent in the disease of obesity. While not yet available to prescribe in Ireland, the development of tirzepatide has reaffirmed hope that as research continues, medical therapy will soon match the biological effects of bariatric and metabolic surgery and provide patients with even more obesity treatment options.
Bariatric and metabolic surgery is the most effective intervention in treating obesity and obesity-associated disease. All procedures are performed laparoscopically with a very low rate of complications. Surgery results in long-term weight loss in the range of 20-to-25 per cent over follow-up periods of 20 years. It also reduces all-cause mortality and ameliorates obesity-related diseases in the long-term.
In diabetes, surgery has particular benefits, and is a more effective treatment for type 2 diabetes than medical care alone. It improves glycaemic control in those with type 2 diabetes, can prevent progression of complications such as diabetic kidney disease, and sometimes results in full remission of type 2 diabetes. Therefore, surgery is increasingly used to primarily treat diabetes rather than the associated obesity.
Weight loss after surgery is not a result of physical restriction or calorie malabsorption, as is commonly misunderstood, but is in fact achieved by modulation of appetite and changes to the physiological response to eating. After surgery, people will experience increased satiety and decreased hunger, which is associated with changes in gastrointestinal hormones such as GLP-1. This reduces appetite and food intake. There is also evidence that surgery increases energy expenditure despite reduced calorie intake, therefore directly addressing the two major components of the disease of obesity.
Surgery is the only treatment with evidence for long-term weight loss, and reduction in all-cause mortality, and therefore should be considered in all people with obesity. While the peri-operative risks are as low as general elective surgery, the long-term effects of these procedures can be intolerable for some, and so the risk of a poor outcome is more often related to the patient’s response to an expected physiological effect of surgery rather than the result of a complication. Before surgery, a comprehensive, holistic multidisciplinary assessment is needed to ensure candidates are fully prepared to have an optimal response to surgery.
Obesity is a disease that affects all aspects of human health, resulting in social isolation, economic disadvantage, disability, obesity-associated diseases, and a reduction in life expectancy. However, obesity is a disease that can be successful treated. Therefore, people with obesity need to be recognised and offered treatment. Treatment can save lives, reduce morbidity and mortality, and improve psychosocial functioning.
We need to do better for people living with obesity, both in terms of our understanding of the disease of obesity as clinicians, and in terms of offering treatment. In 2021, the HSE Model of Care for Obesity was launched. This is the start of a new programme of expanded public sector provision of all treatment options for obesity so that we help people living with obesity to overcome this insidious chronic disease.
References on request