Obesity Overview

Obesity is defined as having a body mass index (BMI) greater than 30. The BMI is a calculation of the body weight with that of the height is used to define underweight, overweight and obesity in individuals. After tobacco, obesity is rated as the second most common cause of preventable death in the U.S. The developing nations have also seen a rise in prevalence of this disease. With rich supply of food and physical labor being reduced due to high dependability on machines, obesity has taken the form of an epidemic. The medical field views obesity as chronic disease which occurs due to years of negligence of health and acts as the pioneer for many leading diseases. Body mass index, also known as the Quetlet index is calculated as weight/height2 where weight is in kilograms and height is in meters. These values are age independent for both the sexes.  WHO classification of obesity
Grade 1 – overweight is a BMI of 25-29.9 kg/m2
Grade 2 – obesity is a BMI of 30-39.9/m2
Grade 3 ‘ severe obesity is greater than or equal to 40 kg/m2   Studies suggest that fat distribution across the body affects the incidences of a concomitant but unrelated pathological or disease processes. A degenerated metabolic process resulting in android obesity could be due to high abdominal fat content including visceral and subcutaneous abdominal fat. Gynecoid obesity is due to heavy fat distribution on the gluteal region.   Though there are still debates over obesity being the cause of a host of concomitant disorder, medicos have observed an aggravation of the underlying pathological or diseased condition whenever a person has diagnosed with obesity.  
Pathophysiology
An increase in adipocytes is said to be the main cause of obesity. Adipocytes are cells that are specialized in synthesis and storage of fats. These cells serve the function of maintaining proper energy balance. They store all the calories in form of lipids and when stimulated they mobilize energy sources in response to hormonal stimulation.   The pathogenesis of obesity is multifaceted and stretches beyond the simple explanation of excess energy intake in comparison to decreased energy output. It been observed that children with obese parents tend to get obese, while in case of twins, mostly if one twin is obese the other one also tends to? be overweight directing the study to the fact that obesity could be genetic in predisposition .  
Etiology
The factors responsible for the development of obesity can be classified as  

• Primary

1. Metabolic factors
2. Genetic factors
3. Level of activity
4. Behavior
5. Endocrine factors
6. Race, sex, and age factors
7. Ethnic and cultural factors
8. Socioeconomic status
9. Dietary habits
10. Smoking cessation
11. Pregnancy and menopause
12. Psychologic factors
13. History of gestational diabetes
14. Lactational history in mothers

• Secondary

1. Hypothyroidism
2. Cushing syndrome
3. Insulinoma
4. Hypothalamic obesity
5. Polycystic ovarian syndrome
6. Genetic syndromes (eg, Prader-Willi syndrome, Alstr??m syndrome, Bardet-Biedl syndrome, Cohen syndrome, B??rjeson-Forssman-Lehmann syndrome, Fr??hlich syndrome)
7. Growth hormone deficiency
8. Oral contraceptive use
9. Medication-related (eg, phenothiazines, sodium valproate, carbamazepine, tricyclic antidepressants, lithium, glucocorticoids, megestrol acetate, thiazolidinediones, sulphonylureas, insulin, adrenergic antagonists, serotonin antagonists [especially cyproheptadine])
10. Eating disorders (especially binge-eating disorder, bulimia nervosa, night-eating disorder)
    Hypogonadism
11. Pseudohypoparathyroidism
12. Obesity related to tube feeding