Overweight and Obesity in children, adolescents and adults have become a major global health problem, a pandemic. Obesity can lead to multiple serious chronic diseases and deaths, and that is why it is important to know how to recognize, manage, and prevent it. BMI (Body Mass Index) provides a simple, inexpensive, and effective method to recognize overweight and obesity.
By WHO statistics in 2016, Obesity has nearly tripled globally since 1975. In that data, 39% individuals (1.9 billion people!) over the age of 18 years were overweight and 1/3rd of them (650 million) were obese. Similarly, millions of children and adolescents were also overweight and obese. The situation and the stats are only worsening over the years, and that, too across the globe.
Today, most of the world’s population is living in countries where overweight and obesity kill more people than underweight. How to manage obesity positively is a great challenge in front of humanity.
What do we exactly mean by Overweight and Obesity?
By WHO’s Overweight and Obesity definition, these terms do not just mean increased weight in an individual. They represent conditions with abnormal or excessive fat accumulation in the body, which is risky for health.
How do we measure the body fat in an individual?
There are many technical ways of measuring body fat. They include measuring skinfold thickness with a caliper, Bioelectrical impedance, Hydro densitometry, Dual-energy X-ray Absorptiometry (DEXA), and Air Displacement Plethysmography. Most of these methods are expensive, sophisticated, and not commonly available. They are mainly used for research purpose.
A simple weight to height measurement index called Body Mass Index (BMI) is a method that comes in handy in day-to-day clinical practice to measure body fat levels.
How is BMI calculated?
BMI is calculated by dividing the individual’s Weight in kilograms by the square of the individual’s Height in meters. Its unit is kg/m2.
BMI = (Weight in kg) / (Height in meters)2
What is the clinical significance of BMI?
As a simple measure of body fat, BMI is useful to judge the healthy and unhealthy weight trends in the community. Its levels are used to clinically define healthy weight, underweight, overweight and obesity in adults. It is same for all adult ages and for both sexes.
| BMI (kg/m2) | Weight Group |
| 18.5- 24.9 | Healthy |
| <18.5 | Underweight |
| 25-29.9 | Overweight |
| >30 | Obesity |
What are the types of Obesity based on BMI?
As per the BMI, Obesity can be Low Risk (Group 1) Obesity, Moderate (Group 2) Obesity and Severe (Group 3) Obesity.
| BMI (kg/m2) | Group |
| 30 – 34.9 | Group 1 – Mild Obesity |
| 35 – 39.9 | Group 2 – Moderate Obesity |
| > 40 | Group 3 – Severe Obesity |
Are there different types of obesity according to body fat distribution?
According to body fat distribution, the obesity has Central and Peripheral types.
In Central Obesity, the fat accumulation is mainly in the abdominal area. Upper arms, upper chest and nape of neck are sometimes involved. It is also called Visceral Obesity because the fat accumulates around important organs (viscera) in the abdomen and chest.
In Peripheral Obesity, the fat accumulation is in hips, buttocks and thighs. It is also called Cutaneous Obesity, as the fat accumulates mainly under the skin.
What is the importance of Apple and Pear shaped body in Obesity?
Apple body shape describes the larger waist and higher abdominal girth of Central Obesity. Since the central obesity fat accumulates around important organs to compromise their blood supply. It is medically more risky for development of serious diseases such as diabetes and heart disease.
Pear body shape describes the smaller waists and bigger hips, buttocks and thighs of Peripheral Obesity. Medically it is less risky for development of serious diseases.
How do we use BMI to recognize Overweight and Obesity in children?
BMI is Age- and- Sex-specific in children and adolescents. It is called BMI-for-Age. There are separate, standardized BMI-For-Age charts for boys and girls.
Plotting percentiles on the WHO BMI-for-Age charts (5-19 years), more than 1 SD (Standard Deviation) above the average is Overweight, and more than 2 SDs above average is Obesity.
Check out WHO BMI-for-Age charts for 5-19 years.
For children less than 5 years of age, WHO advises using Age-Sex-specific Weight-for-Height charts. More than 2 SDs above average is Overweight and more than 3 SDs is Obesity on these charts.
Check out WHO Weight-for-Height charts for 0-5 years.
Using CDC BMI-for-age charts (2-20 years), following guidelines are there.
| Percentile | Weight Pattern |
| Less than 5th Percentile | Underweight |
| From 5th to less than 85th Percentile | Healthy Weight |
| From 85th to less than 95th Percentile | Overweight |
| Above 95th Percentile | Obesity |
Check out CDC BMI-for-Age Charts (2-20 Years).
What is the correct way of checking Weight and Height at home for BMI calculation?
For weight check-up:
- Use a digital weighing scale for accuracy.
- Make sure that the reading is zero and there is no error.
- Placing the weighing scale on a flat floor, the person stands with 2 feet in the center of scale.
- Remove shoes and any heavy clothes.
- Record the weight reading till the nearest first decimal (e.g. 25.4 kg).
For height check-up:
- Person stands on a flat, non-carpeted floor
- with back against a straight wall
- looking straight ahead
- with feet together, shoulders level, and arms at the side of the body
- with head-shoulders-buttocks-heels touching the wall
- Shoes, bulky clothes, hair accessories and headgear (like cap or a cover) are removed.
- With a flat straight head-piece perpendicular to the wall, touch the crown (highest point) of head.
- Mark the lower level on wall.
- Measure with a metal tape from floor to the measured level.
- Take measurement to the nearest first decimal. (e.g.120.2 cm)
Is BMI a perfect fool-proof measure of body fat?
BMI is not perfect or fool-proof- just a rough guide to body fat estimation. Age, sex, ethnicity, and muscle mass can influence the relationship between BMI and Body Fat. BMI does not distinguish between excess fat, muscle, or bone mass. It also does not provide any indication of fat distribution in an individual.
So, in muscular individuals like athletes BMI may overestimate body fat. In women (who typically have more body fat compared to men), and in old people (with loss of muscle mass), it may underestimate body fat.
Despite its limitations, BMI is a simple, inexpensive, and effective method to estimate body fat in a population.
Summary
- Overweight and Obesity lead to serious diseases and even death.
- Obesity is now a pandemic or a global health problem.
- BMI is a simple, practical, and inexpensive method to recognize Overweight and Obesity.
- BMI gives us a rough estimate of body fat, and not a perfect one.
- BMI is calculated by dividing the person’s Weight in kilograms by the square of the person’s height in meters.
- There are BMI for age charts for children.
