What is the Body Mass Index
Most people think about weight in terms of either the bathroom scales or how tight clothes feel around the waist!
The BMI is a better determiner of healthy body weight than weight alone because the calculation factors in your height also. Therefore if your weight is 180 pounds, it is deemed normal if your height is 6ft 2 but obese if you are only 5ft 2.
You have learned in previous sections that measuring your waist with a tape measure is another important method of assessing weight. All methods are useful but using the Body Mass Index (BMI) is of particular value when determining the extra pounds and whether they pose a risk to your health.
We know that Heart Disease, Diabetes and High Blood Pressure are al linked to being overweight. Using a scientific method of assigning a specific value to your weight can help you keep a check on those extra pounds. Although it is not a perfect science when judging your weight, it will provide a fairly accurate assessment of body fat.
When calculating your body fat the BMI takes into account your weight and height and the higher the BMI the greater risk of additional health problems. Your age and gender is also a factor so values will vary accordingly.
So let’s look at the numbers and what they actually mean.
To calculate your BMI, you divide your weight (in kilograms) by the square of your height (in metres).
So, for example, if you weigh 70 kg and are 1.75 metres tall, your BMI is 70/(1.75 x 1.75), which is 22.9.
The percentage is then applied to a chart which determines if you are overweight, normal weight or underweight.
Better still Click Here to try Dr Hall’s BMI Calculator!
An adult BMI of over 30 is considered to be overweight
Between 25 – 29.9 is overweight
Between 18.5 – 24.9 is healthy
Under 8.5 is considered to be underweight
For children BMI decreases during the preschools years then increase gradually as they grow older.
Some Scary Statistics from the last U. S Census and if you are from the U.K you are not very far behind!:
Nearly ⅔ of U. S adults are overweight
Nearly ⅓ of U. S adults are obese
20% of children (ages 6 to 11) that is 1 in 5 were deemed obese
18% of adolescents (ages 12 to 19) were obese
10% of children (ages 2 to 5) were obese
The use of BMI is not for diagnostic purposes but more of a guideline to track your weight issues. Knowledge is power! So knowing your BMI could alert you to potential health problems. These range from urinary stress, gastro esophageal reflux, female infertility, osteoarthritis, hypertension, type ll diabetes, sleep apnea and cardio vascular disease.
If your BMI is too high it should prompt you to take IMMEDIATE ACTION and visit your doctor.
Of course an examination by your doctor will look at more than just your BMI reading. They will look at your medical history, your health risks, your life style, physical activity and diet. And for more a more specific measure of body fatness, your doctor may use equipment such as a dual energy x-ray absorptiometry (DEXA) to test bone density or similar measuring equipment.
BMI useful tool but it has some limitations
Not all doctors rely on BMI and some do not use it at all. The main reason is because it only takes into account your weight and height leaving out other important factors:
- A person’s bone density and size are not considered
Your bone size is determined by ethnicity, family history and other factors. Therefore some people who are naturally big-boned are perfectly healthy and have normal body weight.
- Muscle mass and size is not part of the equation
Muscle mass and size varies from person to person. BMI score may overestimate body fat in an athlete or those with a muscular build due to the size and mass of their muscles. You could be deemed unhealthy, when you are clearly not.
It may underestimate body fat in an older person with significantly less muscle mass deeming them healthy when the opposite could be so.
- Lifestyle is not taken in to account
Your BMI could indicate that you are perfectly healthy but if you are a heavy smoker, drinker or drug user there could be a serious risk to your health due to your life-style choices.
- Family history is ignored
Someone who is considered to be a picture of health based on their BMI score could have a very high risk to chronic disease if family history is not factored in to the assessment.
Knowing your BMI is a good starting point to begin your weight loss journey as a general indicator to body fat. In any event you should undergo an assessment from your doctor before you begin any weight loss program.
At Sharing Self-Improvement there is only a very small emphasis on BMI and I am unlikely to refer to it again.
I do however think it is useful to gain an understanding of BMI and free use of our online BMI calculator.
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