Obesity is defined as excess body fat relative to lean body mass. While humans are well adapted to starvation, they are poorly adapted to overnutrition. The modern high-fat, high-calorie diet combined with physical inactivity has resulted in a global epidemic of obesity and overweight. Although obesity is excess adiposity (adipose tissue is body fat), a convenient parameter of obesity is the body mass index (BMI), which is expressed as body weight (in kilograms) divided by height (in meters) squared. Individuals whose BMI is greater than 30 are obese, whereas those with BMI between 25 and 29.9 are termed overweight. A high BMI level is a risk factor for many diseases and results in high mortality. Obesity may lead to many health complications including diabetes, cardiovascular disease, cancer, and others.
Diabetes
The risk for type-2 diabetes (diabetes due to insulin hormone resistance) increases 60- to 80-fold at a BMI of 30. These two conditions are so commonly associated that they are termed as ‘Diabesity’.
Cardiovascular disease
Obesity is a risk factor for hypertension. This is associated with decreased high-density lipoprotein cholesterol levels and increased low-density lipoprotein cholesterol and triglyceride levels. Weight loss has been shown to improve blood pressure, lipid levels, and diabetes. It is also a risk for coronary heart disease (CHD). In a study published in the New England Journal of Medicine, it was found that the women who had BMI above 30 kg/m2 had a threefold risk for developing nonfatal myocardial infarction compared with women who had BMI below 21kg/m2. Another study done in men found that those who had BMI between 29 and 33 kg/m2 had a twofold risk, and those who had a BMI higher than 33 kg/m2 had a threefold risk for developing CHD compared with men who had a BMI below 23 kg/m2. Additionally, high BMI was also related to the onset of stroke.
Respiratory system disorders
Obesity can have severe adverse effects on the respiratory system. It can cause alterations in respiratory mechanics, respiratory muscle strength and endurance, pulmonary gas exchange, control of breathing, pulmonary function tests, and exercise capacity. Common complaints of obese patients include breathlessness on exertion and exercise intolerance. Obesity is also the most common predisposing factor to obstructive sleep apnea syndrome, particularly in upper body obesity. These episodes are because of occlusion of the airway and may lead to impairment of daytime alertness due to sleep deprivation, increased risk of sleep-related motor vehicle accidents, and increased mortality.
Musculoskeletal disorders
Excess body weight is a well-established risk factor for several types of arthritis, including osteoarthritis, rheumatoid arthritis, and gout. Muscles become relatively weaker because of the inability to perform an exercise. An unsupervised exercise may also lead to muscular injury in the form of tears and hematoma (collection of blood clots).
Cancer
Overweight and obesity are responsible for 15 to 20% of all cancer deaths in men and women. Significant positive associations have been found between obesity and higher death rates for cancer involving the esophagus, stomach, large intestine, liver, gallbladder, pancreas, kidney, prostate, breast, uterus, cervix, and ovary. The increase in breast cancer risk with increasing BMI among postmenopausal women is largely the result of the associated increase in the level of estrogens.
A worldwide strategy for combating obesity, increasing physical activity, and structured exercise should be a high priority. Prevention is clearly more cost-effective than treatment. In certain situations of extreme obesity, the initial bariatric surgery helps the person attain weight when an exercise program is started under medical supervision. Obesity leads to multi-system complications and its management should be handled very delicately.
