In order to understand what is obesity and the exact implications of being obese or overweight, you need to know about the Body Mass Index, often referred to as BMI in short.

BMI is a measurement (arrived at through a calculation), which compares the weight and height of a person to determine the weight status of that person.

It attempts to measure the amount of muscle, fat, and bone mass in an individual and classify him as underweight, of normal weight, overweight or obese.

Obesity Definition

Obesity is defined as an excessive fat deposition in the body to the extent of being a risk to health. It is not just a physiological condition but classified as a serious medical condition.

In other words, obese people are at a health risk because obesity can lead to adverse health conditions and reduced life expectancy.

To exemplify this fact, Sumo wrestlers have a life expectancy between 60 and 65 years, which is 10 years shorter than the lifespan of an average Japanese male. The average BMI of a Sumo wrestler is 36.5

A person is defined as being obese when his or her weight is 20% above what his or her normal weight should be. The BMI parameters tell you what your normal weight should be.

A particular weight may be considered as overweight or obese in a particular person and the same weight need not be considered obese in another.

The criterion is the height of the person. A taller person may be healthy and normal with a particular weight, while a short person will be considered overweight or obese with the same weight.

The height and weight correlation becomes important and this correlation is defined by the Body Mass Index or BMI (described below).

BMI of 30 kg/m² puts you in the obesity category. Another way to express obesity is in the percentage of body weight. The normal amount of body fat in women is between 25-30%  and 18-23% in men. Women with over 30% body fat and men with over 25% body fat are classified as obese.

Such a person is at a very high risk of developing many complications. They include metabolic syndrome, hypertension, atherosclerosis, heart attack, diabetes type 2, high blood cholesterol, and various cancers.

According to a global study, despite institutional efforts, obesity is on the rise in almost every country in the world and in both adults and children. Over the last 30 odd years, it has doubled in most countries.

An obese person can come back to his normal weight by sticking to the right diet, lifestyle changes and adequate physical activity.

However, for some obese persons, bariatric surgery may be required.

What is morbid obesity?

Morbid obesity means that

  • The person has exceeded his or her normal weight by 50% to 100%, or
  • That person is more than 100 pounds above his normal weight.
  • His or her BMI is 40 kg/m² or more.
  • A morbidly obese person is sufficiently overweight to be at a very high-risk exposure to health disorders.

Malignant Obesity

There is also something called as malignant obesity or super obesity where the BMI is 50 or more.

Super-super obesity

Super-super obesity is at the extreme end of the scale where the BMI is 60 or more.

It is relevant to know obesity is considered a complex and chronic disease and which results in various chronic health disorders most of which can be serious. It is the second most leading cause of preventable deaths (Smoking tobacco heads the list).

Even losing weight by 5% to 10% can delay or prevent the diseases, which are caused by obesity.

About Obesity and Being Overweight

A person may be just overweight – that is his or her weight may be more than normal, but that person is considered obese when the weight is much more than just being overweight.

Obesity essentially means having excess fat in the body while overweight means having more than normal weight. Both these conditions carry health risks.

It is just not obesity that puts you at a health risk. Being overweight too is a health hazard.

Researchers also found that having a high BMI was responsible for four million deaths worldwide. Of these, 40% were those people who were overweight and not obese.

This shows that being overweight is almost as much of a risk as being obese.

In the United States, both these conditions are extremely common. 33.70% of its adult population is obese. It ranks at the top among the top ten obese countries (2017).

BMI, a method of measuring the weight of a person in relation to his height helps to determine whether a person is overweight or obese.

Obesity and being overweight are both caused by excessive fat intake and little or no physical activity. It is firmly believed that genetic inclination also plays a major role in making the person obese.

Some stats

According to data from the National Health and Nutrition Examination Survey (NHANES), 2013–2014, for the United States

  • More than 1 in 3 adults were considered to be overweight.
  • More than 1 in 3 adults were considered to be obese.
  • More than 2 in 3 adults were considered to be overweight or have obesity.

According to the World Health Organization,

  • Worldwide, obesity has nearly tripled since 1975.
  • In 2016, more than 1.9 billion adults were overweight. Of these over 650 million were obese.

Assessment of health risk in an obese and overweight person

Besides BMI, two other factors are considered when assessing the health risk of an overweight or obese person.

  • The abdominal girth of the person, because it is the visceral fat or the abdominal fat and not the subcutaneous fat, which is a precursor to health problems.
  • Existing risk factors of the person to health disorders such as diabetes, hypertension and a sedentary lifestyle.

What is BMI or Body Mass Index?

Being overweight or obese is determined by the Body Mass Index or BMI. A BMI between 25 and 30 kg/m² means that the person is pre-obese or overweight while a BMI more than 30 kg/m² is considered as obese.

It is important to know here that BMI does not measure body fat. It only co-relates to the amount of fat in the body.

As a result, athletes who have muscle bulk may have a BMI that classifies them as overweight even though they do not have an excess of body fat.

Such a person will be overweight as obesity is necessarily associated with the excess of adipose (fat) tissue. Obese people are literally fat with an excess deposit of fats in the body. Obesity is easily recognized but very difficult to treat.

How do you calculate BMI?

The formula for BMI was worked out by Belgian mathematician Adolphe Quetelet in the 1830s.

The formula is BMI = weight divided by (height)²

To calculate your BMI:

  • divide your weight measured in kilograms (kg) by your height measured in meters (m)
  • divide the answer by your height again to get your BMI

For example:

  • if your weight is 70 kg and you are 1.75m tall, divide 70 by 1.75 – the answer is 40
  • then divide 40 again by 1.75 – the answer is 22.9, which is your BMI expressed as 22.9kg/m²

This is the metric formula, using kilograms and meters, which is universally used.

The second formula is the English imperial formula, which uses pounds and inches.

BMI = weight in pounds (lb) ÷ height² in inches (in²) × 703 (conversion factor)

How you are categorized:

  • Underweight: Your BMI is less than 18.5.
  • Healthy weight: Your BMI is 18.5 to 24.9.
  • Overweight: Your BMI is 25 to 29.9
  • Obese: Your BMI is more than 30