This has become an important public health problem, which has achieved epidemic levels in the developed world.
This has become an important public health problem, which has achieved epidemic levels in the developed world. In the UK approximately 20% of children and adolescents are either overweight or obese. Obesity in childhood strongly predicts obesity in adulthood. Obesity is an important risk factor for the development of life-threatening disease in later life, including type 2 diabetes mellitus (T2DM), hypertension, cardiovascular disease, and cancer.
Definition and diagnosis
Obesity implies increased central (abdominal) fat mass, and can be quantified using a number of clinical surrogate markers. BMI is the most convenient indicator of body fat mass (see Fig. 12.1).
BMI = weight (kg)/[height (m)]2
- Overweight: BMI >91st centile, wt <98th centile
- Obese: BMI >98th centile
Other measures of obesity include:
- waist circumference;
- waist: hip ratio.
The worldwide increase in the incidence of obesity has been mainly observed in Western countries and in other developed societies. Risk factors for the development of obesity include the following:
- Parental/family history of obesity.
- Afro-Caribbean/Indian–Asian ethnic origins.
- Catch-up growth (weight) in early childhood (0–2yrs): infants born small for gestational age who demonstrate significant weight catch up (>2SDs) in the first 2yrs of life.
So-called idiopathic (or ‘simple’) obesity is by far the commonest cause of obesity accounting for up to 95% of cases. It is multifactorial in origin and represents an imbalance in normal nutritional–environmental–gene interaction, whereby daily calorie (energy) intake exceeds the number of calories (energy) expended:
- genetic predisposition (energy conservation);
- increasingly sedentary lifestyle (energy expenditure);
- increasing consumption and availability of high energy foods.
- Obesity may be associated with other identifiable underlying pathological conditions.
- Cushing’s syndrome/disease.
- Growth hormone deficiency.
- Polycystic ovarian syndrome.
- Acquired hypothalamic injury, i.e. CNS tumours and/ or surgery resulting in disruption to the neuroendocrine pathways regulating appetite and satiety.
Obesity is a recognized feature characterizing the phenotype of a number of genetic syndromes.
- Prader–Willi syndrome.
- Bardet–Biedl syndrome.
- Monogenic causes: leptin deficiency (rare); melanocortin 4 receptor gene (5–6% of all causes).