Obesity is related to most of the common disorders of society: it raises the risk of conditions extending from cancer to chronic liver disease, lung disease, cardiovascular disease and cognitive conditions. Not every person with obesity develops them, and the way the fat is distributed helps determine who does.
Why central fat matters
Independently of total fat percentage, fat in the abdomen and trunk rather than in the pelvic region and lower extremities is associated with a higher risk of metabolic syndrome (a clustering of metabolic risk factors), hypertension and cardiovascular complications, in both men and women. People at higher risk of obesity-related disease are characterised by more of this central fat, on average larger fat cells, a higher number of immune cells within adipose (fat) tissue, and altered signals released from fat that may act directly on the brain, the liver, the vasculature and other organs.
This is why the waist circumference is read alongside the BMI, and why a person with a normal BMI but a raised waist circumference is still considered obese: the risk follows the central fat.
Complications by system
The complications can be grouped by organ system, from the metabolic ones to the psychological and social.
- Metabolic: type 2 diabetes, for which obesity is an independent risk factor and central obesity a particularly strong one; and dyslipidaemia, abnormal levels of blood lipids.
- Cardiovascular: hypertension, coronary heart disease and myocardial infarction, heart failure, atrial fibrillation and stroke. Obesity contributes directly to several of these risk factors at once.
- Respiratory: obstructive sleep apnoea, for which obesity is one of the leading risk factors because fat around the neck and upper airway predisposes to airway collapse during sleep. Untreated sleep apnoea in turn raises the risk of heart disease and diabetes, and may itself worsen obesity.
- Liver: fatty liver disease, now termed metabolic dysfunction-associated steatotic liver disease.
- Musculoskeletal: osteoarthritis.
- Cancer: endometrial, breast, ovarian, prostate, liver, gallbladder, kidney and colon cancer are among those associated with obesity.
- Psychological and social: depression and low self-esteem are linked both to obesity and to the stigma attached to overweight, with consequences in personal and working life.
Taken together, these conditions cause premature death and substantial disability, and obesity is associated with a reduced life expectancy.