Body Mass Index (BMI) is the measure of the total body fat. It estimates weight in relation to a person’s height. It is calculated by dividing weight in kilograms by the height in square meters (m2). The BMI can be different in people of same age and sex as their body weight may differ. In other words, we can say that the difference may arise due to variation in body fat. However, there are exceptions too. In some cases, the figure may not be estimated correctly. Sometimes, it may overestimate body fat for body builders, athletes and pregnant women.
BMI calculations will under rate the amount of body fat in the elderly and in people with physical disabilities like those who are not able to walk.
Also, BMI measures are not correct for people, who have eating disorders like anorexia nervosa or who are suffering from extreme obesity.
Once you understand what BMI is, you need to know what BMI range is normal and what is considered as overweight or underweight.
If the BMI range is:
| Less than 18.5 | Underweight |
| 18.5-24.9 | Normal for young and middle-aged adults |
| 25.0-29.9 | overweight |
| More than 30 | obesity |
BMI does not distinguish between body fat and muscle mass. So, it may not give the exact measurement for the following groups:
- Muscle Builders: People, who add muscles to their body or are body builders have a high BMI, but they are not overweight.
- People with Physical Disabilities: Physically disabled people, who can not walk may have muscle wasting. Their BMI may be lower, but it does not mean that they are underweight. In such a case, it is better to consult a dietitian.
- Height: BMI is dependent of height, so it may over rate obesity among shorter people and under rate in people, who are comparatively taller. Thus, BMI cannot be used for people, who are too short or too tall.
- Ethnicity: Indians and people from Asian descent have more body fat for any given BMI as compared to those of European origin. So, the range for obesity and overweight will be lower for these people.
BMI and Children
We have seen that the healthy or normal BMI range for adults is 18.5-24.9. However, children are constantly growing, so we cannot have any set values of BMI for them. Besides, adults, who are no longer growing show an increase in BMI due to increase in body fat. But, since children are in their growing years, the amount of body fat keeps on changing and gets reflected in the BMI.
Risks of Being Overweight
If you are overweight and do not do any physical activity, then you are at a higher risk of developing:
- Cardiovascular disease
- Gallbladder disease
- Osteoarthritis
- Type 2 diabetes
- Hypertension
- Colon and breast cancer
- Mental illnesses like depression
Risks of Being Underweight
If you are underweight, you may develop the following conditions:
- Suppressed immune system
- Digestive disorders
- Respiratory illnesses
- Osteoporosis
- Cancer
If there is excess fat around a person’s abdomen, which is generally called “pot belly,” it may signal that one has greater chances of developing obesity-related health conditions. Fat accumulated around the hips or buttocks may not pose similar health risks. In men, the deposition of fat is generally seen around waist and so, they have greater chances of developing obesity-related conditions. Studies say that body fat distribution is associated with incidence of diabetes, hypertension and cardiovascular disease.
Incidentally, genes are responsible for depositing the fat around the belly. But, it does not mean that you cannot do anything about it. There is still hope. To shed abdominal fat, you must be physically active, cut down on smoking, and replace saturated fats with unsaturated fats.
Thus, it can be concluded that BMI is a simple calculation of the relationship between height and weight of a person. Greater the BMI, more overweight you are. Doctors and health care providers use BMI in estimating the health of the patients. However, this method has some weaknesses. The first issue is that it does not provide accurate estimate for the body fat. Another concern is that the BMI indicators for men and women may be different when in fact, they may have same body fat percentage. Last but not the least, if there are more muscles in the body, it may give wrong BMI reading.
BMI is the relative measure of body’s weight with respect to the height. However, it has its some limitations and may not be considered as an accurate measure of overweight, underweight or obesity. Read on to know when you should be concerned in relation to your BMI.
