BMI: a flawed method?

Lately we've been asked by many program participants why we are not giving Healthy Lifestyles points based on BMI and rather are basing our points of "weight loss" on body fat percentage. To understand why we do this, please consider the facts behind BMI and body fat...


BMI stands for Body Mass Index. BMI is calculated by taking into consideration your total body weight and your total height. The exact equation is your body weight in pounds multiplied by 703, then divide that number by your height in inches squared. Results are categorized as follows:

• Underweight = <18.5
• Normal weight = 18.5–24.9
• Overweight = 25–29.9
• Obesity = BMI of 30 or greater

BMI has been used as a screening tool to identify possible weight problems for individuals. Unfortunately, there are many flaws in this method...

BMI makes no allowance for the relative proportions of bone, muscle, and fat in the body. Since muscle weighs more than fat and since bone is denser than muscle and twice as dense as fat, a person with strong bones, good muscle tone, and low fat may have a high BMI. Thus, athletes and fit, health-conscious individuals may be classified as "overweight" or even "obese". 


BMI also does not account for body frame size; A person may have a genetically small frame and be carrying too much excess fat, but their BMI reflects that they are "healthy". Conversely, a large framed individual may be quite healthy with a fairly low body fat percentage, but be classified as "overweight" or "obese" by BMI. 


A further limitation of BMI relates to loss of height through aging. In this situation, BMI will increase without any corresponding increase in weight.


Another problem with BMI is that it does not include an analysis and understanding of race and ethnicity. Consider the following statistics:

• A BMI of 25 (.1 above the "normal" range and into the "overweight" range) is associated with the lowest death rate for white men and women.
• A BMI of 27 (2.1 beyond the "norm") is associated with the lowest death rate for African-American men and women.
• Native-Americans with a BMI between 35 and 40 (more than 10 points above "normal" and even categorized as "obese") do not have an increased risk of death despite being above the set standard.
• A BMI of less than 20 is associated with a higher mortality rate (risk of death), although the National Heart, Lung, and Blood Institute standards say that a BMI as low as 18.5 is "normal".

The last problem I'll mention (though there are many more flaws that could be discussed) is that the BMI scale suggests sharp distinctions between "underweight", "ideal", "overweight", and "obese", and this can be very harmful to individuals in society, especially children and adolescents. While children tend to grow in size and weight faster than they grow in height, the categories they are placed into could be severely  flawed and detrimental as it relates to comments and teasing. According to the US Department of Agriculture, 1 of 4 "at risk" children (BMI 85-95%ile) actually have normal body fat, and 1 of 6 in the "normal" range have elevated body fat. This suggests that weight needs to be understood in context of a child's individual growth history, fitness, activity, and eating behaviors. However, when we allow BMI scales to classify our children as "overweight" and "obese", this encourages weightism. They are stereotyped, judged as morally lacking, and are considered otherwise inferior. Additionally, exposure to weight related comments or teasing increases the risk of weight concerns, loneliness, lower confidence in physical appearance, and higher preference for isolative activities which is associated with decreased levels of physical activity and poor eating habits, only exacerbating the problem. It also increases a child's risk of developing eating disorders.


Hopefully this allows you to see why BMI is not always an accurate predictor of health and rather carries with it many harmful effects Consequently we've decided to focus more on body fat percentage than BMI, which we feel carries a more accurate assessment of health, as having too much or too little fat both increase your risk for chronic disease. 


We like to conduct our tests with a HEALTH-centered approach in mind rather than a weight-centered approach for reasons described above. Weight-centered approaches toward health are a result of a thinness bias, where all that is "thin" is considered good and all that is "fat" is considered bad. Additionally, when weight is the focus, intentional weight loss (dieting) is often seen as the solution; however, 95-98% of dieting results in weight regain and damages body functions. Those who engage in dieting behaviors are far more likely to have excessive body fat as primary weight loss among the dieting industry is made up of water weight and muscle mass (not to mention the weight of money in your pocket) while training your body to hold on to more fat. In summary, there is no better way to train your body to gain weight/fat than to go on a diet. 

Remember, also, that body fat percentage is only one aspect of health. Your blood pressure and cholesterol are also important measurements. To improve or maintain health, make sure you do at least 30 minutes of physical activity most days of the week, eat nutritious foods (plenty of fruits, veggies, and whole grains), drink at least 8 glasses (64 oz) of water a day, visit with your healthcare providers regularly (stay on top of physical, dental, colonoscopy, mammogram/pap/prostate exams, etc), manage stress, and sleep approximately 8 hours a night. These things will also naturally result in obtaining/maintaining a healthy weight and body composition, more so than any weight-loss pill or diet program, no matter how successful they claim to be. 

Post Title : BMI: a flawed method?

BMI: a flawed method?,

weight loss,

BMI: a flawed method?