Obesity in absolute terms is an increase of body fatty tissue mass. In a practical setting it is difficult to measure this directly, and obesity is typically measured by BMI (body mass index) and in terms of its distribution through waist circumference or waist-hip circumference ratio measurements. In addition, the presence of obesity needs to be evaluated in the context of other risk factors and co morbidities (other medical conditions that could influence risk of complications)
BMI
Body mass index or BMI is a simple and widely used method for estimating body fat mass. BMI was developed in the 19th century by the Belgian statistician and anthropometrist Adolphe Quetelet. BMI is an accurate reflection of body fat percentage in the majority of the adult population, but is less accurate in situations that affect body composition such as in body builders and pregnancy.
BMI is calculated by dividing the subject's weight by the square of his/her height, typically expressed either in metric or US "Customary" units:
Metric: BMI = kg / m2
Where kg is the subject's weight in kilograms and m is the subject's height in metres.
US/Customary and imperial: BMI = lb * 703 / in2
Where lb is the subject's weight in pounds and in is the subject's height in inches.
The most commonly used definitions, established by the WHO in 1997 and published in 2000, provide the following values
• 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 30.0–34.9 is class I obesity
• A BMI of 35.0-39.9 is class II obesity
• A BMI of > 40.0 is class III obesity or severe / morbidly obese
• A BMI of 35.0 or higher in the presence of at least one other significant co morbidity is also classified by some bodies as morbid obesity
Waist circumference and waist hip ratio
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.
In a cohort of almost 15,000 subjects from the National Health and Nutrition Examination Survey (NHANES) III study, waist circumference explained obesity-related health risk significantly better than BMI when metabolic syndrome was taken as an outcome measure.
Other body fat measurements
- 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 skin fold 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).
Risk factors and co morbidities
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 apnoea 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.
Effects on health
Mortality
- Mortality risk varies with BMI.
- The lowest risk is found at a BMI of 22-24 kg/m2 and increases with changes in either direction.
- A BMI of over 32 is associated with a doubling of risk of death.
Morbidity
- 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 apnoea, social stigma) or increased number of fat cells (diabetes, some forms of cancer, cardiovascular disease, non-alcoholic fatty liver disease). There are alterations in the body's response to insulin (insulin resistance), a pro inflammatory 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 metabolic syndrome, obesity is related to a variety of other complications. Some are directly caused by obesity well others are more indirectly related, such as sharing a common cause like poor diet or sedentary lifestyle.
- Cardiovascular: congestive heart failure, enlarged heart and its associated arrhythmias and dizziness, 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: erectile dysfunction, urinary incontinence, chronic renal failure, 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, idiopathic intracranial hypertension
- Respiratory: obstructive sleep apnoea, obesity hypoventilation syndrome, asthma
- Psychological: Depression, low self esteem, body dysmorphic disorder, social stigmatization
Causes
Most researchers agree that a combination of excessive calorie consumption and a sedentary lifestyle are the primary causes of obesity in the majority of the population. Other less well established or minor influences include genetic causes, medical and psychiatric illnesses, and microbiological causes.
A 2006 review identifies ten other possibly under investigated causes for recently increasing rates of obesity:
(1) Insufficient sleep,
(2) Endocrine disruptors - food substances that interfere with lipid metabolism,
(3) decreased variability in ambient temperature,
(4) decreased rates of smoking, which suppresses appetite,
(5) increased use of medication that leads to weight gain,
(6) Increased distribution of ethnic and age groups that tend to be heavier,
(7) Pregnancy at a later age,
(8) Intrauterine and intergenerational effects,
(9) Positive natural selection of people with a higher BMI,
(10) Assortative mating, heavier people tending to form relationships with each other.
Dietary
Sedentary lifestyle
- An increasingly sedentary lifestyle plays a significant role in obesity.
- There has been a trend toward decreased physical activity due in part to increasingly mechanized forms of work,
- Changing modes of transportation, and increasing urbanization.
- Studies in children and adults have found an association between the number of hours of television watched and the prevalence of obesity.
- Driving one's children to school also decreases the amount of exercise that these children get and has led to calls for reduced car use around schools.
- An association between leisure time activity and obesity has been found.
Genetics
Like many other medical conditions, obesity is the result of interplay between genetic and environmental factors. Polymorphisms in various genes controlling appetite, metabolism, and adipokine release may predispose to obesity when sufficient calories are present. Obesity is a major feature in a number of rare genetic conditions: Prader-Willi syndrome, Bardet-Biedl syndrome, MOMO syndrome, leptin receptor mutations, melanocortin receptor mutations. In a people with early-onset severe obesity (defined by an onset before ten years of age and body mass index over three standard deviations above normal),Medical illness
Certain physical and mental illnesses and the pharmaceutical substances used to treat them can increase one's risk of obesity. Medical illnesses that increase obesity risk include several rare genetic syndromes (listed above) as well as some congenital or acquired conditions:
(1) Hypothyroidism,
(2) Cushing's syndrome,
(3) Growth hormone deficiency,
(4) Eating disorders such bulimia nervosa, binge eating disorder and compulsive overeating.
Certain medications may cause weight gain and or negative changes in body composition, such as steroids, atypical antipsychotics, some fertility medication, insulin and sulfonylureas.
Microbiological
The role of bacteria colonizing the digestive tract in the development of obesity has recently become the subject of investigation. Bacteria participate in digestion (especially of fatty acids and polysaccharides), and alterations in the proportion of particular strains of bacteria may explain why certain people are more prone to weight gain than others. Human digestive tract bacteria are generally either member of the phyla of bacteroidetes or of firmicutes. In obese people, there is a relative abundance of firmicutes (which cause relatively high energy absorption), which is restored by weight loss. From these results it cannot be concluded whether this imbalance is the cause or effect of obesity.
Social determinants
- The correlation between social class and BMI is inconsistent. Comparing net worth with BMI found obese Americanians approximately half as wealthy as thin ones. When income differentials were factored out, the inequity persisted. A tendency to rely on fast food is seen as one of the reasons why this result occurred. Another study found women who married into a higher social class are thinner than women who married into a lower social class.
- Men from lower middle income households were less likely to be obese than were those in the highest income households and women from middle income households had the highest rates of obesity.
- Cessation of smoking verse continued smoking can leads to weight gain. A study found that those who quit smoking gained 4-5 kilograms over ten years. One sixth of the rise in obesity in North Americans can be attributed to falling rates of smoking.
Treatment for obesity
- Eating less and exercising more.
- Diet programs -Healthy diet
- Anti-obesity drug
Homeopathy medicines works well for Obesity
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