BMI Calculator – Body Mass Index

What is Body Mass Index?

Body Mass Index or BMI is a parameter calculated by using the tissue mass and height of a person. The tissue mass includes muscles, fat as well as bones. We can describe it as the body mass divided by the body height's square. Thus it is expressed in terms of kg/m2. The BMI calculator is basically used for knowing the deviation of the person's body weight from the normal. This excess or deficiency is considered to be body fat, though there is muscularity and other factors which affect the BMI remarkably.

How are people categorized using the Body Mass Index Calculator?

BMI is the best way to categorize people on the basis of their height and tissue mass. Though the exact dividing line between the classes is still under debate, we have some commonly accepted BMI ranges. These are as follows:

1. Underweight - The BMI is below 18.5 kg/m2
2. Normal Weight - In this case, the BMI ranges from 18.5 to 25
3. Overweight - The BMI range for overweight individuals is from 25 to 30 or more. Overweight and obesity issues are generally seen among Americans and is the least in Southeast Asia.

How reliable is the Body Mass Index?

The BMI of an individual doesn't remain the same if we double the body dimensions, as mass scales with the cube of height. It actually becomes double, which implies an unusually high BMI for taller people. This indicates the unreliability of the parameter in measuring the fat level of an individual. There is another parameter named Ponderal Index or Corpulence Index that was initially started by Swiss physician Fritz Rohrer. It uses natural scaling of mass with the third power of height to attain realistic results, unlike BMI. So, it is reliable. The fat mass and muscle mass distribution assumptions are never accurate. If we consider the example of people with more lean mass such as the athletes, BMI makes an overestimation of their adiposity. Similarly, in the case of the people with lean body mass, the excess adiposity is underestimated. Studies indicate that this parameter is better in determining if a person is not obese rather than determining if a person is obese. It is seen that those in the BMI range 20-30 comes under a wide range of body fat percentages. People who are very fit will have an inaccurate BMI because their high muscle mass will categorize them under the overweight class. Parameters such as body volume index are better determinants of obesity measurement in such cases.

What are the children's BMI within the age group 2-20?

A recent study conducted in Britain indicates a higher BMI of females of the age group 12-16 by 1 kg/m2 on an average, compared to the males of the same age. In the case of kids, there is a variation in the method of measuring BMI. The calculated BMI is compared with those of other kids of their age instead of any fixed threshold as in the case of adults. The comparison of the BMI is done against the percentile for children of similar age and gender.

The kids BMI classifications

1. When the kids BMI is less than 5th percentile, it is categorized as underweight.
2. Obese kids are those with a BMI exceeding 95th percentile.
3. Kids BMI between the 85th and 95th percentile are classified as overweight.

What are health implications associated with abnormal BMI ?

When the calculated BMI of people is below 20 or above 25, it leads to numerous health problems such as:

• Increased chances of mortality even in the case of non-smokers.
• Dyslipidemia
• Type 2 diabetes
• Hypertension
• Osteoarthritis
• Cancers such as colon cancer, endometrial cancer, breast cancer.
• Epidural lipomatosis
• Sleep apnea
• Stroke
• Coronary artery disease
• Gallbladder disease

What are common uses of the Body Mass Index?

This parameter is used for the following purposes:

1. Correlating the groups linked by general mass - This helps in the estimation of adiposity in a vague manner. It is primarily helpful in the trend recognition in case of sedentary or overweight individuals owing to small error margin.WHO has been using it since the 1980s as the means of measuring obesity statistics. As per the cross-sectional studies, the BMI of sedentary people can reduce when they become physically active.
2. Use in clinical practice - This BMI Calculator is a reliable tool to measure the category to which the sedentary individuals belong, i.e. underweight, normal or overweight. The exceptions include kids, athletes, the infirm and elderly people. In the US, it supports people with eating disorders such as bulimia nervosa and anorexia nervosa.
3. Legislation related to the BMI - There are laws to ensure that people interested in fashion can fight anorexia with ease. So, fashion models having a BMI below 18 have been banned in countries like Italy, France, and Spain. In Israel also, those with a BMI less than 18.5 can't opt for modeling.

Parameters alternative to BMI

Here are some of the more reliable parameters:

1. 1. BMI Prime This is the ratio of actual BMI and upper limit optional BMI (25 kg/m2). The upper limit optimal BMI differs with places. For example, it is 23 instead of 25 for the South East Asian and South Chinese populations. The parameter indicates the deviation of the person's weight from the highest optimal BMI. Classification as per the BMI Prime is as follows:
      • Underweight: BMI Prime is below 0.74
      • Normal weight: BMI Prime lies between 0.74 and 1.00
      • Overweight: Such people have a BMI Prime greater than 1.00
   2. Waist Circumference:It helps in indicating visceral fat which poses a serious health risk compared to the fat in other areas of the body. It has been defined by the National Institutes of Health (NIH). When it exceeds 102 cm in men and 88cm in non-pregnant women, the different health issue can occur. This includes dyslipidemia, hypertension, CVD and high probability for type 2 diabetes. In Asians, serious health implications occur when it is 94 cm for men and 80 for men, but the NIH figures are even more.
   3. The ratio of waist circumference to the height of an individual is also a good indicator. Following values indicate a risky case:
      • It exceeds 0.5 for people less than 40 years old
      • In the age group of 40-50, the value is 0.5-0.6
      • For people over the age of 50 years, it is 0.6
       
   4. Surface-based body shape index or SBSI This parameter takes 4 measurements into consideration, i.e. vertical trunk circumference (VTC), the body surface area (BSA), height(H) and the waist circumference (WC). It is calculated as the product of height raised to 7/4 power and the WC raised to 5/6 power, which is then divided by the product of BSA and VTC.
   5. Modified body mass index or mBMI It is produced by factoring serum albumin in certain medical contexts as familial amyloid. Mathematically, the formula of mBMI is the product of BMI and Serum albumin which is measured in terms of grams/liter.