Morbid obesity, also known as clinically severe obesity, is an abnormal obesity defined as the condition of having body weight over 100 Ibs over an ideal body weight or having a body mass index (BMI) of 40 or higher. A BMI of 35.0 or higher in the presence of at least one other significant comorbidity is also classified by some bodies as morbid obesity.

In recent years, morbid obesity has also become present in both children and teenagers due to the childhood obesity epidemic. As evident in western culture, children have began to become more overweight than their parents and grandparents were when they were children, partially due to technology such as computers and television, as well as the possibly daily intake of fatty meals.

In practical settings, obesity is typically evaluated in absolute terms by measuring BMI (body mass index), but also in terms of its distribution through waist circumference or waist-hip circumference ratio measurements.In addition, the presence of obesity needs to be regarded in the context of other risk factors and comorbidities (other medical conditions that could influence risk of complications).

It is calculated by dividing the subject's weight by the square of his/her height.
Metric: BMI = kg / m2
Where kg is the subject's weight in kilograms and m is the subject's height in metres.
The most commonly used definitions, established by the WHO in 1997 and published in 2000, provide the following values:

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A few interesting facts :

BMI does not take into account differing ratios of adipose to lean tissue; nor does it distinguish between differing forms of adiposity, some of which may correlate more closely with cardiovascular risk. Increasing understanding of the biology of different forms of adipose tissue has shown that visceral fat or central obesity (male-type or apple-type obesity, also known as "belly fat") has a much stronger correlation, particularly with cardiovascular disease, than the BMI alone.
The absolute waist circumference (>102 cm in men and >88 cm in women) or waist-hip ratio (>0.9 for men and >0.85 for women) are both used as measures of central obesity.

An alternative way to determine obesity is to assess percent body fat. Doctors and scientists generally agree that men with more than 25% body fat and women with more than 30% body fat are obese. However, it is difficult to measure body fat precisely. The most accepted method has been to weigh a person underwater, but underwater weighing is a procedure limited to laboratories with special equipment. Two simpler methods for measuring body fat are the skinfold test, in which a pinch of skin is precisely measured to determine the thickness of the subcutaneous fat layer; or bioelectrical impedance analysis, usually only carried out at specialist clinics. Their routine use is discouraged.

Other measurements of body fat include computed tomography (CT/CAT scan), magnetic resonance imaging (MRI/NMR), and dual energy X-ray absorptiometry (DXA).

The presence of risk factors and diseases associated with obesity are also used to establish a clinical diagnosis. Coronary heart disease, type 2 diabetes, and sleep apnea are possible life-threatening risk factors that would indicate clinical treatment of obesity. Smoking, hypertension, age and family history are other risk factors that may indicate treatment.

A large number of medical conditions have been associated with obesity. Health consequences are categorised as being the result of either increased fat mass (osteoarthritis, obstructive sleep apnea, social stigma) or increased number of fat cells (diabetes, cancer, cardiovascular disease, non-alcoholic fatty liver disease).Mortality is increased in obesity, with a BMI of over 32 being associated with a doubled risk of death. There are alterations in the body's response to insulin (insulin resistance), a proinflammatory state and an increased tendency to thrombosis (prothrombotic state).
Disease associations may be dependent or independent of the distribution of adipose tissue. Central obesity (male-type or waist-predominant obesity, characterised by a high waist-hip ratio), is an important risk factor for the metabolic syndrome, the clustering of a number of diseases and risk factors that heavily predispose for cardiovascular disease. These are diabetes mellitus type 2, high blood pressure, high blood cholesterol, and triglyceride levels (combined hyperlipidemia).
Apart from the metabolic syndrome, obesity is also correlated with a variety of other complications. For some of these complaints, it has not been clearly established to what extent they are caused directly by obesity itself, or have some other cause (such as limited exercise) that causes obesity as well.

The main treatment for obesity is to reduce body fat by eating fewer calories and exercising more. Diet and exercise programs produce an average weight loss of approximately 8% of total body mass (excluding program drop-outs). Not all dieters are satisfied with these results, but a loss of as little as 5% of body mass can create large health benefits.
Much more difficult than reducing body fat is keeping it off. Eighty to ninety-five percent of those who lose 10% or more of their body mass by dieting regain all that weight back within two to five years. Therefore, keeping weight off generally requires making exercise and eating right a permanent part of a person's lifestyle.

Sleeve gastrectomy is a surgical weight-loss procedure in which the stomach is reduced to about 35% of its original size, by surgical removal of a large portion of the stomach, following the major curve. The open edges are then attached together (often with surgical staples) to form a sleeve or tube with a banana shape. The procedure permanently reduces the size of the stomach. The procedure is performed laparoscopically and is not reversible.

Sleeve gastrectomy is usually performed on extremely obese patients, where the risk of performing a gastric bypass or duodenal switch procedure may be too large. A two-stage procedure is performed: the first is a sleeve gastrectomy, and the second is a conversion into a gastric bypass or duodenal switch. Patients usually lose a large quantity of their excess weight after the first sleeve gastrectomy procedure alone, but if weight loss ceases the second step is performed.

Like any surgical operation, sleeve gastrectomy has possible complications, such as leakage, dilation of the sleeve (which allows for more food intake) and other usual complications associated with bariatric surgery, though the risks are known to be much lower than in RNY gastric bypass and duodenal switch.