Introduced in the s, this measure considers a person's weight in relation to their height. A normal BMI is Despite its popularity, BMI is widely considered to be a flawed metric. It fails to consider vital influencing factors such as body type, gender, age, and bone density. Moreover, BMI can't distinguish between muscle and fat.
This can lead to clearly inaccurate results, particularly in athletes. For example, professional wrestler "Stone Cold" Steve Austin in his prime was a heavily muscled picture of physical fitness—but his 6'2" height and lb kg weight gave him a BMI of Because of results such as these, BMI is a fairly imprecise determiner of whether or not a given person is overweight.
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Why, almost 60 years after he first appeared in the Daily Mirror, is a layabout lout from north-east England still so loved around the world? At a basic level, weight gain — eventually leading to being overweight or obesity — is determined by a balance of energy.
This is a called an energy surplus. When we consume less energy than we expend, we lose weight — this is an energy deficit. This means there are two potential drivers of the increase in obesity rates in recent decades: either an increase in kilocalorie intake i.
Both elements are likely to play a role in the rise in obesity. Over the past century — but particularly over the past 50 years — the supply of calories has increased across the world. In the s, the global average supply of calories that is, the availability of calories for consumers to eat was kcal per person per day. By this had increased to kcal. Across most countries, energy consumption has therefore increased.
If this increase was not met with an increase in energy expenditure, weight gain and a rise in obesity rates is the result. In the chart here we see the relationship between the share of men that are overweight or obese on the y-axis versus the daily average supply of kilocalories per person.
Overall we see a strong positive relationship: countries with higher rates of overweight tend to have a higher supply of calories. Most countries move upwards and to the right: the supply of calories has increased at the same time as obesity rates have increased. The most common metric used for assessing the prevalence of obesity is the body mass index BMI scale.
For example, an adult who weighs 70kg and whose height is 1. Measured BMI values are used to define whether an individual is considered to be underweight, healthy, overweight or obese. The WHO defines these categories using the cut-off points in the table. For example, an individual with a BMI between The metric for measuring bodyweight in children and adolescents is also the body mass index BMI scale, measured in the same way described above.
Whilst there is no differentiation of weight categories in adults based on sex or age, these are important factors in the body composition of children.
Factors such as age, gender and sexual maturation affect the BMI of younger individuals. For interpretation of individuals between the ages of 2 and 20 years old, BMI is measured relative to peers of the same age and gender, with weight classifications judged as shown in the table.
The merits of using BMI as an indicator of body fat and obesity are still contested. Whilst physicians continue to use BMI as a general indicator of weight-related health risks, there are some cases where its use should be considered more carefully 14 :.
Physicians must therefore evaluate BMI results carefully on a individual basis. Despite outlier cases where BMI is an inappropriate indicator of body fat, its use provides a reasonable measure of the risk of weight-related health factors across most individuals across the general population.
The United States has the 12th highest obesity rate in the world at This is due to the same dietary, environmental, and cultural factors that cause variations between countries.
Diet is primarily to blame, with Americans receiving mixed messages about what they should be eating and how much of it.
Faced with mouth-watering advertisements served alongside campaigns promoting daily physical activity and proper nutrition, many Americans opt for fast, cheap, and filling options such as processed packaged food, fast food, and larger portions. This often leads to a diet rich in fat, calories, and sodium the "butter, sugar, salt" trifecta and low in vitamins and nutrients. For a full list of the world's countries and their obesity rates and average BMIs, see the table below. Obesity Rates By Country BMI explained The most commonly used method of measuring obesity is the Body Mass Index, or BMI, which divides a person's weight in kilograms by their height in meters squared.
Obesity by country Obesity rates vary significantly by country as a result of different lifestyles and diets.
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