Dr. Sheikh Mansoor, Dr. Vikas Sharma
Obesity is a complex, multifactorial, lifestyle-related disorder which dominantly affects nearly one-third of a global population.
In more than one way, obesity classifies as a potential indicator or contributing factor of various clinical conditions, subsequently leading to poor health outcomes and compromised quality of life. Obesity can be defined in terms of BMI i.e. body mass index that can be calculated as weight (kg) divided by height squared (m2). US centers for disease control and prevention (CDC) and WHO collectively identify a normal BMI range of 18.5-24.9 kg/m2 for adults, however, BMI 25 kg/m2 is categorized as overweight, BMI 30kg/m2 as obese and BMI 40 kg/m2 as severely obese.
Classification BMI (kg/m2)
Underweight <18.5
Normal weight 18.5-24.9
Overweight 25.0-29.9
Obese Class I 30.0-34.9
Obese Class II 35.0-39.9
Obese Class III ? 40
The major contributing factor is disbalance in chronic energy (energy intake from food exceeds energy expenditure), surplus energy conversion into triglyceride (fat) and storage of fat in adipose tissues, subsequently causing increased body mass and weight gain. For the past five decades, the prevalence of overweight/obesity has enhanced worldwide toward pandemic. The major complications are:
Diabetes: Currently over 12% of adults in the US have diabetes and this is projected to rise to 21-33% by 2050. Most patients with type 2 diabetes (T2DM) are obese and the global epidemic of obesity largely explains the explosion in cases of T2DM over the past two decades.
Hypertension: About half of the overweight individuals are hypertensive and obesity itself is the cause of 70% of essential hypertension. With an increase in body weight, cardiac output increases but the weight of the heart in comparison to total body weight remains lower than in normal-weight controls. In obesity, increased cardiac output is the result of increased sympathetic activity. As noradrenaline levels are higher in obesity, adrenaline levels remain normal, therefore lower response of adrenaline to hypoglycaemia and exercise was observed. Also, in obesity, the expression of adipose angiotensinogen gene gets elevated and resulting in increased circulating levels of angiotensinogen. Other studies also suggest the obesity-associated decrease in the concentration of atrial natriuretic peptide and ventricular natriuretic peptides (natural antagonists of the RAAS). This may also serve as the basis of obesity-induced hypertension. In adverse conditions, renal hyper-filtration, glucose intolerance, hyperlipidaemia and hypertension all together can contribute to obesity-induced focal segmental glomerulosclerosis.
Dyslipidaemia: The effects of obesity on lipid metabolism include high low-density lipoprotein cholesterol, very low-density lipoprotein cholesterol, triglycerides and low levels of the protective high-density lipoprotein cholesterol.
Stroke: Obese individuals have been shown to be twice as likely to have a stroke, either ischaemic or haemorrhagic, than people with a BMI of < 23. Even after adjusting for other risk factors, excess weight was still associated with increased risk.
Cancer: It is estimated that obesity accounts for 20% of all cancer cases. A large-scale review by the International Agency for Research on Cancer concluded that obesity was the cause of a quarter to one-third of cancers of the colon, breast, endometrium, kidney and oesophagus. It is also associated with increased risk of gastric, pancreatic and gallbladder cancer, as well as leukaemia. Furthermore, prognosis is poorer in obese individuals who develop some cancer types. One study found obese women with breast cancer were found to be 46% more likely to develop distant metastases and 38% more likely to die than lean counterparts. Chemotherapy and radiotherapy dosing is more difficult with up to 40% of obese patients receiving limited chemotherapy doses that are not based on their body weight. Weight loss has been shown to reduce the risk of some cancers; it has been shown to lessen the risk of breast cancer, particularly among postmenopausal women.
Obstructive sleep apnoea: Obstructive sleep apnoea (OSA) adversely affects multiple systems and is associated with hypertension, insulin resistance, liver dysfunction, systemic inflammation and dyslipidaemia. In children, it can lead to failure to thrive, behavioural problems, decreased intellectual function and a higher risk of cardiovascular morbidity. Obesity has long been known to be a major pathogenic factor in OSA in adults. A study of 4000?US adults found prevalence was 12% in obese vs. 3% in lean subjects. In children, OSA was primarily felt to be due to adeno-tonsillar hypertrophy. However, with increasing levels of childhood obesity, this has changed. Whereas < 15% of all habitually snoring children were obese in the early 1990s, by 2006, this figure had risen to >50%.
Kidney disease: Overweight and obesity are risk factors for hypertension, diabetes, and other conditions associated with impaired renal function. A study following up over 8 million person-years found that, compared with lean people, the relative risk for End-Stage Renal Failure (ESRF) was 1.87 for overweight individuals, 3.57 for those with class I obesity, 6.12 for those with class II obesity, and 7.07 for those with class III obesity. After adjusting for other risk factors, higher BMI remained an independent predictor of ESRF. Obesity is also associated with greater risk of kidney stones and urinary incontinence in women, while obesity-related glomerulopathy has increased in prevalence in parallel with obesity.
Fertility: In men, obesity is associated with reduced sperm count and increased rates of erectile dysfunction. In women, it also leads to reduced fertility, poorer outcomes after fertility treatment and more pregnancy loss. Polycystic Ovarian Syndrome (PCOS) is the primary cause of female infertility and increases the rate of pregnancy complications. The risk of PCOS is slightly increased with obesity and obese women with PCOS often have a more serious phenotype.
Psychosocial: Obese individuals are often exposed to public disapproval and stigma due to their weight, with women experiencing more discrimination. This takes place in employment, healthcare, education and other areas. Depression is more common in obesity, particularly in women and younger people, while weight loss is associated with improved mood. Adolescents who are obese or overweight, or perceive themselves as such, are more likely to engage in risk behavior than those of normal weight. This can involve substance abuse, risky sexual behavior or violence.
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