BMI (body mass index) and body fat percentage are weight-loss terms thrown around with little explanation, so if you’re confused about what they mean or which you should pay more attention to, you’re not alone. Here’s a brief primer to help.
BMI stands for Body Mass Index. It’s a simple measure of the weight of a person scaled according to their height. You can or follow these steps to determine your BMI:
Your weight in pounds X 703 = X. X / by your height in inches = Y. Y / your height in inches = BMI.
- Multiply your weight in pounds by 703.
- Divide that answer by your height in inches.
- Divide that answer by your height in inches again.
A healthy BMI is between 18.5 and 24.9.
Problems With The BMI Chart
BMI is a blunt measuring instrument. All of the BMI studies in the research were done across large populations. Using that data and applying it to an individual without looking at the person’s overall health is a bad idea. BMI calculations do not consider age, gender, frame size, muscle mass, or fat distribution. Subcutaneous fat (under the skin) does not appear to strongly predispose to disease, whereas visceral fat (in and between the organs) does. Therefore, someone can have a normal BMI but a high percentage of visceral fat and be at high risk for diabetes and heart disease but a sumo wrestler, with a high BMI but little visceral fat, will be metabolically healthy. Additionally, as most people know, essentially all NFL running backs and body builders, most of whom sport 6-packs and sub-10% body fat would be classified as obese under this system. Even a recreational athlete with slightly above average muscle mass could be considered overweight.
Many doctors calculate the BMI of patients and make recommendation simply based on that number, which is a flawed approach for the reasons given above. In fact, I just saw a patient for physique coaching who was 5’9” and weighed 185 pounds. Despite having a 33 inch waist, 11% body fat and perfect cholesterol and blood sugar, his primary care doctor told him he must lose 25 pounds if he didn’t want to get diabetes and heart disease!
A BMI of less than 18.5 classifies a person as underweight; between 18.5 and 24.9 as normal; between 25 and 29.9 as overweight; 30 and 39.9 as obese and over 40 as morbidly obese. You must also keep in mind that these numbers were calculated on Caucasian male and female populations. BMI does not take into account differences in body composition between genders, race/ethnicity groups and across the life span.
Researchers are using another method, a low-dose X-ray called DXA, to estimate bone density, lean mass and fat mass. Based on the DXA reading, the researchers found that an African American woman, for example, may not be overweight or obese even though the BMI formula, which considers a person’s height and weight, indicates that she is. Currently, non-Hispanic white women are not considered obese until they have a BMI of 30 or above, for African American women, the number to cross is 32. Women in other racial and ethnic groups were considered obese even if their BMI number was below 30. The results were similar in men. The discrepancies are due to variations in bone mineral content, hydration state and the density of lean mass in different ethnic groups.
Better Alternatives to The BMI Chart
Body fat percentage is the weight of a person’s fat divided by the person’s weight.
Weight of a person’s fat / total body weight = Body fat %
Body fat % lets you see how much of your body is made up of fat, and how much is bone, muscle, blood, and organs. There are several ways to calculate your percentage. Your skin folds can be gently pinched with calipers, some high-tech scales can measure body fat, ( I have a scale that measures body weight, body fat, body water weight, muscle mass and bone mass) and there’s also underwater weighing. Many people get their body fat percentage measured if they are into sports or trying to measure their progress while losing weight.
1) Body fat measurement: While BMI is used as proxy for body fat, it is a much better idea to just measure body fat. Health is generally better with lower body fat percentages regardless of the BMI, and this includes populations with documented diseases like diabetes. I recommend striving for maximum muscle mass and a body fat below 15% for men and 23% for women. These numbers are within the “fitness range” of recommended body fat according to the American Council on Exercise.
Body Fat % for Men & Women
Athlete 6 – 13 14 – 20
Fitness 14 – 17 21 – 24
Average 18 – 24 25 – 31
Obese 25 32
2) Waist to hip circumference: Since it is becoming very clear that the distribution of body fat is an important indicator is disease risk, it makes sense to examine it. People with fat distributed around the abdomen are at higher risk for heart disease and diabetes, so aiming to reduce the ratio is a better idea than trying to reduce BMI. (Asian ethnicities are more prone to carry more body fat around the middle than other ethnicities and so need to be more careful.)
Waist-to-hip ratio (WHR) is the ratio of your waist circumference to your hip circumference (calculated by dividing the waist circumference by the hip circumference). WHR is a measurement tool that looks at the proportion of fat stored on your waist, and hips and buttocks. Weight concentrated around the middle is often referred to as an “apple” shape; whereas, weight concentrated around your hips is referred to as a “pear” shape.
In many cases, persons with extra weight located around the middle are at higher risk for diseases such as heart disease and diabetes than those who carry weight around their hips and thighs. Abdominal fat, when out of proportion to total body fat, may be considered an indicator of health risks. A waist circumference measurement of over 35 inches in women and over 40 inches in men may increase risk because of the fat distribution.
To measure your waist and hip circumferences:
Using a tape measure to check your waist circumference, measure the distance around the smallest area of your waist, usually just above the belly button.
Using a tape measure to check your hip circumference, measure the distance around the largest area of your hips, usually the widest part of the buttocks. Find an online hip to waist calculator and enter your numbers.
For men, a ratio of .90 or less is considered safe.
For women, a ratio of .80 or less is considered safe.
For both men and women, a WHR of 1.0 or higher is considered “at risk” for heart disease and other problems associated with being overweight.
In summary, just focusing on “losing weight” is not a good idea. You need to know all your numbers. In my patient education program, we show you all your nutrition numbers in Step 4, “Learn About Nutrition”. If you only focus on losing “weight” you may very well end up losing muscle as well and looking like a shrunk down version of your former self, with the same risk of serious disease as before. Just because you are thin doesn’t mean you are healthy.
As always, it is important to look at the “big picture” rather than focusing on a particular calculation to evaluate your chances of developing an obesity-related illness.
As always, please leave your comments or questions below. We love hearing from you!
Any nutritional information or dietary advice is not intended as a treatment or therapy for any disease or particular bodily symptom. Nutritional counseling, food recommendations, nutritional advice and vitamin, mineral and/or phytochemical support are provided solely to upgrade the quality of foods in the patient’s diet in order to support the physiological and biomechanical processes of the human body. We make no warranties or representations expressed or implied as to the accuracy or completeness, timeliness or usefulness of any opinions, advice or information contained or referenced in this material. We also do not assume any risk for your use of this information. Any statements made have not been evaluated by the Food and Drug Administration.
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