Obesity

Obesity is a complicated and often discriminated-against medical condition in which being overweight affects one's health. It is a common and significant problem in modern industrialized countries. This of course has led to the inevitable woo-meisters pushing fad diets of every shape and kind, and do-gooders and politicians trying to improve our children's eating habits by such things as banning sodas containing high-fructose corn syrup from school lunchrooms, and revisiting the food groups pyramid  tree plate every year to make tweaks in the recommendations. Obesity is the world’s fifth leading risks of death globally, according to the World Health Organization. At least 2.8 million adults die each year as a result of being overweight or obese, WHO estimated in 2008 — significantly less than the 9.1 million estimated to die of hunger in the same period. Contrary to stereotype, the U.S is not actually the most obese nation in the world.

How to recognise obesity
System of body Condition Scoring

Body mass index
The "body mass index" (BMI) is a comparison of height to weight (i.e. if you are 4 feet tall but weigh 140 pounds, you're obese, but if you are 8 feet tall and weigh 140 pounds, then you're severely underweight). It was originally devised as an obesity indicator for populations, and so sometimes produces misleading results for individuals.

BMI scales poorly with height at its extremes, exaggerating thinness in shorter individuals and fatness in taller ones (for example, Yao Ming — 7'6" and 310 lbs — was "overweight" during his All-Star NBA career), and by definition cannot distinguish between muscle and fat (NFL quarterback and 2010 Super Bowl MVP Aaron Rodgers — 6'2" and 225lbs — has an "overweight" BMI of 28.9, just under the 29.9 cutoff for obese). On the other end, it can also underestimate obesity, and up to 30% of people with a "normal" BMI may have the same elevated metabolic risk factors for heart disease and diabetes as those classified as obese. BMI also says nothing about an individual's fitness and activity level.

As a population metric, BMI is meant to be an approximation metric for percentage of body fat. There are more direct tests for body fat percentage, based on body density or bioelectric impedance, but these measurements are more difficult to make or require specialized equipment. Lacking skinfold calipers, a body fat scale, or a massive tank of water, other easy-to-measure metrics, such as waist-to-height ratio or waist-to-hip ratio may be a better gauge to judge health risks of obesity as they appear to correlate more strongly with morbidity and health risks. All of these methods are best used in conjunction with other health indicators, such as age, blood pressure, and so on.

Being within the overweight-but-not-obese range used to be considered as serious a health risk as obesity. However, a 2013 meta-analysis of 2.88 million individuals across 97 studies found that the opposite is true: people who were overweight were 6% less likely to die prematurely than those of normal weight. Even Category 1 obesity (BMI 30-34.9, about 175-200 pounds for someone 5'8" tall) was associated with no elevated risk of death, though Category 2 or higher raised the risk by 30%. This illustrates two things: one, dose matters, for body fat as much as drugs; and two, the optimum BMI range for health is both higher and wider than the optimum for social desirability.