bmi classification

BMI has been debated within the health industry for years. From exhausting quick diet schemes to changing eating habits, many have tried to reach the ideal BMI.

The real question is, does BMI really reflect your overall health and well being? To answer this question, I decided to do a bit of research to help you make an informed decision.

What is BMI?

Body mass index (BMI) is a parameter used by medical professionals to determine if you are underweight, normal weight, overweight or even obese. It is expressed as a ratio of weight to height, calculated as weight in kilograms divided by the square of height in meters (kg/m2). When calculating BMI, only height and weight are taken into account. The calculation doesn’t take into account any other factors like gender, age, fitness levels, ethnicity or body structure which are all factors that have a significant impact on your body weight status.

BMI is used by physicians and health professionals worldwide since it is a simple, noninvasive and inexpensive way to determine if someone is obese and suffering from health risks linked to obesity. BMI is also used to screen population health on a big scale.

You can find out your personal BMI here.

The biggest critique of the BMI comes from the fact that only weight and height can’t determine body fat percentage accurately. That’s why it’s possible to be overweight according to BMI but still have a lean and healthy body, or in the normal range but with a high body fat percentage.

Categories according to BMI

When you go to your physician and ask him about your weight he will put you in some of these categories, according to your BMI. These categories are used for people from 20 years of age and older. BMI for children is calculated the same way but is compared to different charts.

underweight person
Underweight ( BMI less than 18.5)

People with a BMI less than 18.5 are underweight and may suffer consequences from malnutrition. A low BMI can also indicate eating disorders. These people need to change their diets so they get all needed nutrients from food and accomplish weight gain.

normal bmi

Normal range (BMI 18.5-24.9)

People with a BMI in this range are considered to have a healthy weight.

 

overweight person
Overweight (BMI 25-30)

A person with a BMI between 25-30 is considered overweight and could suffer from health risks associated with overweight like hypertension, high triglyceride levels, diabetes, stroke, coronary heart disease, … A weight loss plan should be considered.

obese personObese (BMI greater than 30)

People who have a BMI higher than 30 are considered obese. There are different categories of obese – Obese I (BMI 30-35), Obese II (30-40) and Morbidly obese (BMI greater than 40). People in the obese category should change their diets and start an exercise program to reduce their body weight. Most people in this category suffer from several health risks associated with too much body fat.

You can calculate your personal BMI here.

Where it is flawed

Body fat percentage and body fat distribution are much more important factors for your overall health than weight and height. BMI calculations take into account solely weight and height and can not define body fat percentage accurately. BMI doesn’t make a difference between bones, muscles and fat and doesn’t take into account where you’re weight is coming from. That’s why it is possible that a person with a large and heavy bone structure has a healthy weight, body fat percentage and body physic but is considered overweight according to BMI. The BMI does not distinguish if the weight comes from fat, heavy bones or muscles.



You can’t make a direct parallel between BMI and body fat percentage for every individual routinely. That’s why individuals with very little lean muscle mass but a high body fat percentage can be categorized into a normal BMI range. These people are in danger of having health complications due to high body fat like hypertension, diabetes or stroke. Their incorrect placement into the normal body weight range may prevent them from getting help in time.

The overweight athlete

BMI is often wrong for very fit people and athletes who have lot of muscles and lean mass. They are often considered overweight although they have low body fat percentages and are in fact very healthy and fit. Lot of their weight is linked to muscles who are heavier than fat which makes them overweight according to BMI. BMI doesn’t distinguish between the weight of the healthy lean mass, bones and body fat. That’s why BMI measurement is not applicable to very fit individuals and athletes.

Type of fat

One more limitation of the BMI is the fact that BMI doesn’t distinguish between the type of fat in a persons body. Fat can be stored right under our skin (subcutaneous fat) or internally around our organs (visceral fat). All people have both types of fat but it is far more dangerous to have more visceral fat stored around your stomach and heart than fat under the skin. Visceral fat is the dangerous fat that can increase the chance of having serious health problems like coronary heart diseases, stroke, diabetes,.. BMI can not distinguish between these two types of fat.

same bmi but different fat distribution

Image of two different individuals with same BMI but different fat distribution

That’s why two people can have the same BMI but with a completely different fat distribution. It is much more important for the person with visceral fat to lose weight. Simple BMI measurement can mask this problem preventing individulas to lose weight on time.

Age, gender and ethnicity limitation

Also factors like age, gender and ethnicity are not taken into account when BMI is calculated. These factors do have a significant impact on body weight and overall health.

  • Age
    Older people naturally lose height and muscle but gain fat. Body fat percentage and body fat distribution is much more important in these individuals since their BMI can be misleading. Older people should be checked for body fat  amount and distribution since a normal BMI with an older person can indicate that this person has more fat than lean mass. A change in diet and exercise may be crucial to maintain a healthy active lifestyle.
  • Gender
    The calculation and categories for BMI are completely the same for men and women, although women naturally have more fat than men.
  • Ethnicity
    For some ethnic groups research has shown that the categories of BMI do not apply. For example Asians can experience obesity-related health problems already with a BMI of 23 and higher. It seems that Asians are having more body fat than Caucasians making them more vulnerable to diseases like diabetes 2 and cardiovascular disease.

Doesn’t have to change with your diet and fitness level

If you have decided to lose weight and want to reach your ideal BMI by exercising and eating healthy you maybe surprised that your BMI or weight maybe won’t change at all but your body composition and physic will. When losing weight by exercising your body fat can be displaced with muscles which are heavier than fat. This way if you have to lose only a few pounds it is very possible that your weight and BMI won’t change, but your body composition will, which will make you stronger and healthier. On the other hand if you experience huge weight loss from the obese category to the normal range you will definitively see a difference in your BMI as well.

It is important to say that weight loss is not always noticeable on the scale which shouldn’t make you frustrated or confused about your body image since fat loss and muscle gain is far more important than simple BMI reduction.

Other simple measurements

Most physicians today use BMI as an initial tool to see if you’re overweight or obese, combined with some other measurements that can indicate possible weight-related health risks. Waist Circumference has proved to be a simple but very indicative measurement for your overall health.

The measurement of your waist is a very good indicator of possible health risks due to overweight and body fat. Research published in the monthly journal of the Association of  Physicians shows that women with a waist circumference greater than 35 inches (88 cm) or men with a measurement greater than 40 inches (100 cm) have increased health risks, such as diabetes and heart disease. Even with a BMI in the normal range these individuals should take weight loss into consideration.

Women with a waist circumference greater than 35 inches (88 cm) or men with a measurement greater than 40 inches (100 cm) have increased health risks, such as diabetes and heart disease.

Also body fat percentage can be inexpensively and roughly calculated by measuring height, neck, waist, hips and weight. Combined with BMI, waist circumference and rough body fat percentage measurement are as simple and inexpensive to use like BMI but give a more accurate picture of your body composition.

Although BMI is a useful tool for rough estimation of body weight it has  limitations when it comes to weight assessment for individuals. BMI does not reflect body fat percentage, fat distribution or fat type all of which are more accurate predictors for weight associated health risks. Although BMI is a good indicator for the obese it can be misleading and prevent certain individuals to regulate their weight in time before serious health risks appear. That’s why BMI should only be one of the factors to watch out for when losing weight. Body composition and fat distribution should also be key factors to a healthier weight.

I still keep track of my BMI to be in the normal range as a helpful tool to check my weight, but I consider all the other factors as well. Do you care what your BMI is?