The Obesity Epidemic
Obesity is a condition in which the natural energy reserve, stored in the fatty tissue of humans and mammals, is increased to a point where it is a risk factor for certain health conditions or increased mortality. Obesity develops from the interaction of individual biology and the environment. Excessive body weight has been shown to correlate with various diseases, particularly cardiovascular disease, diabetes mellitus type 2, sleep apnea, and osteoarthritis. Obesity is both an individual clinical condition and is increasingly viewed as a serious public health problem.
Definition
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. A BMI of 30.0 - 39.9 is obese, and a BMI of 40.0 or higher is severely (or morbidly) obese
Waist circumference
BMI does not take into account differing ratios of fat to lean muscle tissue. 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) 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.
Body fat measurement
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.
Risk factors
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. Diabetes and heart disease are risk factors used in epidemiological studies of obesity.
Factors that have been suggested to contribute to the development of obesity include:
- Genetic factors and some genetic disorders (e.g., Prader-Willi syndrome)
- Underlying illness
- Certain medications (e.g., atypical antipsychotics)
- Sedentary lifestyle
- A high glycemic diet
- Yo-yo dieting
- Eating disorders (binge eating)
- Stressful mentality
- Insufficient sleep
- Smoking cessation
As with many medical conditions, the caloric imbalance that results in obesity often develops from a combination of genetic and environmental factors. 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.
Complications
Obesity, especially central obesity (male-type or waist-predominant obesity), is an important risk factor for the "metabolic syndrome" ("syndrome X"), 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). An inflammatory state is present, which — together with the above — has been implicated in the high prevalence of atherosclerosis (fatty lumps in the arterial wall), and a prothrombotic state may further worsen cardiovascular risk.Cardiovascular: congestive heart failure, enlarged heart and its associated arrhythmias and dizziness, cor pulmonale, varicose veins, and pulmonary embolism
Endocrine: polycystic ovarian syndrome (PCOS), menstrual disorders, and infertility Gastrointestinal: gastroesophageal reflux disease (GERD), fatty liver disease, cholelithiasis (gallstones), hernia, and colorectal cancer
Renal and genitourinary: urinary incontinence, glomerulopathy, hypogonadism (male), breast cancer (female), uterine cancer (female), stillbirth
Integument (skin and appendages): stretch marks, acanthosis nigricans, lymphedema, cellulitis, carbuncles, intertrigo
Musculoskeletal: hyperuricemia (which predisposes to gout), immobility, osteoarthritis, low back pain
Neurologic: stroke, meralgia paresthetica, headache, carpal tunnel syndrome, dementia.
Respiratory: dyspnea, obstructive sleep apnea, hypoventilation syndrome, Pickwickian syndrome, asthma
Psychological: Depression, low self esteem, body dysmorphic disorder, social stigmatization
While being severely obese has many health ramifications, those who are somewhat overweight face little increased mortality or morbidity. Some studies suggest that the somewhat "overweight" tend to live longer than those at their "ideal" weight. This may in part be attributable to lower mortality rates in diseases where death is either caused or contributed to by significant weight loss due to the greater risk of being underweight experienced by those in the ideal category. Another factor which may confound mortality data is smoking, since obese individuals are less likely to smoke. Osteoporosis is known to occur less in slightly overweight people.
Treatment
The best treatment for obesity is a calorie controlled diet and increased exercise. In studies, diet and exercise programs have consistently produced an average weight loss of approximately 8% of total body mass. 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.
Bariatric surgery is becoming more common. 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.
All of these surgeries come with risk to the patient. For instance a recent study by the U.S. Department of Health and Human Service showed a 40% complication rate within 180 days of bariatric surgery. Moreover these surgeries do not guarantee either successful weight loss or reduced morbidity and mortality. Patients are also required to to make lifelong changes to their diet if they are to keep the lost weight off in the long term. Therefore, as with any major surgery, patients needs to carefully evalute the long term ramifications of their choice.
Further reading
World Health Organization - Obesity pages Diet, Nutrition and the prevention of chronic diseases (including obesity) by a Joint WHO/FAO Expert consultationSponsored Resources