OBESITY

Obesity is the term used to describe the condition of being overweight due to excess body fat. A person is considered obese if they have a body mass index (BMI) of 30+.

Obesity is both an individual clinical condition and a serious public health problem. Excessive body weight has been shown to predispose to various diseases, particularly cardiovascular diseases, diabetes mellitus type 2, sleep apnoea, and osteoarthritis.

In the clinical setting, obesity is typically evaluated by measuring BMI (body mass index), waist circumference, and evaluating the presence of risk factors and comorbidities. In epidemiological studies, BMI alone is used to define obesity.

BMI

Body Mass Index (BMI) is a simple and widely used method for estimating body fat. It is calculated by dividing the subject's weight in kilograms by the square of his/her height in metres:

BMI = kg / m²

The current definitions:

* A BMI less than 18.5 is underweight
* A BMI of 18.5 - 24.9 is normal weight
* A BMI of 25.0 - 29.9 is overweight
* A BMI of 30.0 - 39.9 is obese
* A BMI of 40.0 or higher is severely (or morbidly) obese
* 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.

BMI is a simple and widely used method for estimating body fat. In epidemiology BMI alone is used as an indicator of prevalence and incidence.

BMI as an indicator of a clinical condition is used in conjunction with other clinical assessments, such as waist circumference.

In a clinical setting, physicians take into account race, ethnicity, lean mass (muscularity), age, sex, and other factors which can affect the interpretation of BMI.

BMI overestimates body fat in persons who are very muscular, and it can underestimate body fat in persons who have lost body mass (eg. elderly).

Mild obesity as defined by BMI alone is not a cardiac risk factor, and hence BMI cannot be used as a sole clinical and epidemiological predictor of cardiovascular health.

Causes

In its simplest conception, obesity is only made possible when the lifetime energy intake exceeds lifetime energy expenditure by more than it does for individuals of "normal weight".

When food energy intake exceeds energy expenditure, fat cells (and to a lesser extent muscle and liver cells) throughout the body take in the energy and store it as fat.

Factors that have been suggested to contribute to the development of obesity include:

* Genetic factors and some genetic disorders (eg. Prader-Willi syndrome)
* Underlying illness (eg. hypothyroidism)
* Eating disorders (eg. binge eating disorder)
* Certain medications (eg. atypical antipsychotics)
* Sedentary lifestyle
* Depression
* A high glycaemic diet (ie. a diet that consists of meals that give high postprandial blood sugar)

As with many medical conditions, the caloric imbalance that results in obesity often develops from a combination of genetic and environmental factors. Polymorphisms in various genes controlling appetite, metabolism, and adipokine release predispose to obesity, but the condition requires availability of sufficient calories, and possibly other factors, to develop fully. Various genetic abnormalities that predispose to obesity have been identified (such as Prader-Willi syndrome and leptin receptor mutations), but known single-locus mutations have been found in only about 5% of obese individuals. While it is thought that a large proportion of the causative genes are still to be identified, much obesity is likely the result of interactions between multiple genes, and non-genetic factors are likely also important.

Some eating disorders are associated with obesity, especially binge eating disorder (BED). As the name indicates, patients with this disorder are prone to overeat, often in binges. A proposed mechanism is that the eating serves to reduce anxiety, and some parallels with substance abuse can be drawn. An important additional factor is that BED patients often lack the ability to recognize hunger and satiety, something that is normally learned in childhood. Learning theory suggests that early childhood conceptions may lead to an association between food and a calm mental state.

Treatment

The mainstay of treatment for obesity is an energy-limited diet and increased exercise. In studies, diet and exercise programs have consistently produced an average weight loss of approximately 8% of total body mass on average (excluding study drop-outs). While not all dieters will be satisfied with this outcome, studies have shown that a loss of as little as 5% of body mass can create enormous health benefits.

A more intractable therapeutic problem appears to be weight loss maintenance. Of dieters who manage to lose 10% or more of their body mass in studies, 80-95% will regain that weight within two to five years. It appears that the homeostatic mechanisms regulating body weight are very robust (see leptin, for example), and vigorously defend against weight loss. Much important research is now being devoted to determining what factors can improve the currently dismal weight loss maintenance rates.

Recent scientific research has cast some doubt over whether or not dieting actually improves health, with some studies indicating that dieting may in fact be more detrimental than remaining overweight.

In a clinical practice guideline by the American College of Physicians, the following five recommendations are made:

1. People with a BMI of over 30 should be counseled on diet, exercise and other relevant behavioral interventions, and set a realistic goal for weight loss.
2. If these goals are not achieved, pharmacotherapy can be offered. The patient needs to be informed of the possibility of side-effects and the unavailability of long-term safety and efficacy data.
3. Drug therapy may consist of sibutramine, orlistat, phentermine, diethylpropion, fluoxetine, and bupropion. For more severe cases of obesity, stronger drugs such as amphetamine and methamphetamine may be used on a selective basis. Evidence is not sufficient to recommend sertraline, topiramate, or zonisamide.
4. In patients with BMI > 40 who fail to achieve their weight loss goals (with or without medication) and who develop obesity-related complications, referral for bariatric surgery may be indicated. The patient needs to be aware of the potential complications.
5. Those requiring bariatric surgery should be referred to high-volume referral centers, as the evidence suggests that surgeons who frequently perform these procedures have fewer complications.

Much research focuses on new drugs to combat obesity, which is seen as the biggest health problem facing developed countries. Nutritionists and many doctors feel that these research funds would be better devoted to advice on good nutrition, healthy eating, and promoting a more active lifestyle.

Medication most commonly prescribed for diet/exercise-resistant obesity is Orlistat (Xenical, which reduces intestinal fat absorption by inhibiting pancreatic lipase) and Sibutramine (Reductil, Meridia, an anorectic).

In the presence of diabetes mellitus, there is evidence that the anti-diabetic drug metformin (Glucophage) can assist in weight loss — rather than sulphonylurea derivatives and insulin, which often lead to further weight gain. The thiazolidinediones (rosiglitazone or pioglitazone) can cause slight weight gain, but decrease the "pathologic" form of abdominal fat, and are therefore often used in obese diabetics.

Increasingly, bariatric surgery is being used to combat obesity. The most common weight loss surgery in Europe and Australia is the adjustable gastric band where a silicone ring is placed around the top of the stomach to help restrict the amount of food eaten in a sitting. It is considered the safest and least invasive of the available weight loss surgeries such as Roux-en-Y gastric bypass surgery (RNY), biliopancreatic diversion, and stomach stapling (also known as "vertical banded gastroplasty", VBG). Unlike those more invasive techniques the band surgery does not cut into or reroute any of the digestive tract and is completely reversible. Removing the implant returns the stomach to its pre-surgical norm. All of these surgeries can be done laparoscopically. The more invasive of the surgeries usually bypass or remove some portion of the patient's intestines which causes malabsorption and dumping.

All of these surgical procedures carry some risk and complication rate can be as high as 40%. Moreover these surgeries do not guarantee either successful weight loss or reduced morbidity and mortality. Patients are also required to make lifelong changes to their diet if they are to keep the lost weight off in the long term.

Source: wikipedia GFDL