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ENDOCRINOLOGY FOCUS OBESITY
Obesity: The Disease and the Available Treatments Written by Dr Karl J Neff St Vincent’s Health Group, Dublin Diabetes Complications Research Centre, Conway Institute, University College Dublin
the amount of body fat present, and so responds to reduced food intake as part of a planned calorie controlled diet in the same way as it would response to starvation: it activates two powerful physiological systems that prevent weight loss.6-8
Obesity the Disease Obesity is a disease that affects all facets of health and wellbeing, and is associated with a wide range of diseases, including type 2 diabetes, cardiovascular disease and cancer.1, 2 The morbidity associated with obesity is so significant that it limits life expectancy.3 As well as the effects on physical health, obesity has chronic and debilitating effects on psychosocial health and function. Obesity is associated with poor mental health outcomes, reduced social participation, reduced economic opportunity, and reduced quality of life.4-5 The negative effects of obesity on psychosocial function and health are partially attributable to obesity stigma. Obesity stigma is the term used to refer to discrimination based on weight. In our society, many feel free to openly discriminate against people based on their weight. People with obesity are very likely to encounter stigma both in everyday life and in healthcare encounters. Obesity stigma manifests in many ways. It most commonly manifests in public life in media commentary that describes people with obesity as ‘fat and lazy’ that could (but won’t) make better food choices
and do more exercise in order to lose weight. This narrative leaves people living with obesity feeling very alone in a world that judges them for their disease. In healthcare, we are just as prone to obesity stigma as any other section of society. People with obesity often avoid presenting to healthcare providers with medical symptoms as they expect that every symptom will be attributed to their weight, and that they will not be listened to. Instead they will likely be told that things would get better if they would ‘just lose some weight’: something that they have probably heard and tried to do many times before (usually without success). Obesity stigma is a result of a fundamental misunderstanding of obesity as a moral choice rather than a disease. For the majority of people with obesity, the physiological regulation of body fat is dysfunctional and metabolic maladaptation has developed that prevents sustainable weight loss. This means that when people with obesity try to lose weight, physiological mechanisms are activated that defend against loss of body fat. In obesity, the hypothalamus (the energy homeostat of the body) has lost the ability to accurately gauge
JULY 2022 • HPN | HOSPITALPROFESSIONALNEWS.IE
The first physiological defence mechanism is hunger. Reduction in food intake results in increased hunger. Hunger is an unconscious physiological reflex that can be consciously controlled to an extent. People on a diet consciously resist their hunger in an effort to lose weight. For people who do not have obesity, this can be done with relative ease. If we do not have obesity, then the hypothallus recognises the adipose stores present and so moderates any increase in appetite. However, people with obesity will be persistently hungry, and often have increased hunger, while on a diet.6-8 While they can consciously resist their hunger, with great effort, to achieve at least some weight loss, living in a constant state of perceived starvation is challenging to maintain. For those that do sustain longterm resistance of hunger, and achieve weight loss, the second major physiological maladaptation comes into play. This is alteration of the basal metabolic rate. If hunger does not stimulate calorie ingestion, then the hypothalamus will downregulate the basal metabolic rate so that we burn fewer calories.8-10 This is why people usually find that despite sticking to a diet that initially resulted in weight loss (while feeling extremely hungry throughout), they ultimately hit a weight loss plateau. This occurs because the energy homeostat adjusts energy expenditure downwards to meet the reduced calorie intake. This means that people will continue to burn fewer calories for as long as there is a net calorie deficit. The only way to overcome this mechanism is to consciously
reduce calorie intake to extremely low levels below the minimum basal metabolic rate needed for survival (i.e. a ‘starvation diet’ which for most equates to less than 600kcal per day). However, even if someone can achieve this, reintroduction of a diet with a calorie intake within recommended limits (e.g. 2000kcal per day) will produce weight regain, as their healthy 2000kcal a day diet will be in excess of the calories that they are expending by the end of their diet (which could be less than 1000kcal per day).8-10 Therefore, weight regain occurs as they are consuming more calories than they are burning. Treating Obesity Given these powerful physiological mechanisms, obesity is a very difficult disease to treat. However, treatment should be actively offered to people with obesity as successful treatment results in improved physical health, with significant benefits in the prevention and treatment of obesity associated diabetes, cardiovascular disease and cancer. These benefits in physical health occur in tandem with myriad benefits in psychosocial health and functioning. Diet and Exercise Based Approaches Given the two pathophysiological mechanisms inherent in the disease of obesity described above, it should be no surprise that for the majority of people with obesity, diet and exercise interventions alone will not achieve durable weight loss. Diet and exercise based treatment can be very effective in a small number of people. However, for most people with obesity diet and exercise based approaches are insufficient to treat the disease and result in significant weight loss.11-14 This is not due to lack of adherence with the programme. Lack of weight loss in response to diet and exercise intervention is usually due to the physiological defences against weight loss described above.8-10, 12 At best, approximately 20% of people with obesity will achieve significant weight loss with diet and exercise programmes alone, meaning that 80% or more will not.13 However, diet and exercise programmes are very unlikely to cause harm and so, while ineffective in most people,
