Body mass index (BMI) is not a reliable indicator of overweight and obesity, in spite of what the National Heart Lung and Blood Institute says. Body fat percentage is the key information that you should have for assessing your weight and health risks. Here is why.

Calculating Body Mass Index

You can look up your BMI based on your height and weight at the bottom of this post. That would be a lot easier than calculating it yourself. Nevertheless, to understand why this index is unreliable, it is instructive to first take a look at how the BMI is calculated.

The formula for body mass index (BMI), with an example for the same person in English and metric units, is:

English Units: BMI = Weight (lb) x 703 / Height (in) x Height (in)

Example: 195 lbs x 703 / 73 inches x 73 inches = 25.7

Metric Units: BMI = Weight (kg) / Height (m) x Height (m)

Example: (86.6 kg / 1.85 m x 1.85 m) = 25.3

(The small difference in these results, starting with the same height and weight, are due to rounding errors in converting from English to metric units.)

The NHLBI says that the following are meaningful BMIs for adults between the ages of 18 and 65 years:

Weaknesses of the BMI

We can all probably agree that overweight and obesity are a global epidemic. Obesity alone is a significant risk factor for dying from a heart attack, regardless of whether other known risk factors are present. Obesity is also believed to contribute to other serious health conditions including high blood pressure, high cholesterol, Type II diabetes, gallbladder disease, osteoarthritis, sleep apnea, and respiratory problems, as well as endometrial, breast, prostate, and colon cancers. That is a good slew of individual issues that I may pick apart in another post (e.g., the myth of high cholesterol). For now, let’s just focus on BMI vs. body fat, which is what we want to know in the first place.

In particular, let’s take a look at the comment on this page of the NHLBI: “BMI is a useful indicator of overweight and obesity.”

This and other pages at the NHLBI site quickly point out variables that the BMI fails to account for:

• BMI varies by sex, race, and age
• At the same BMI, women tend to have more body fat than men
• At the same BMI, older people, on average, tend to have more body fat than younger adults
• Highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness

Here is an interesting contradiction: I have a close friend who is 64 years old and has maintained a weight of about 205 lbs for the past 20 years. His height 20 years ago was 5′ 10″ (70 inches), which calculates to a BMI of 29.4. Recently, due to normal bone loss, he is closer to 5′ 8″ (68 inches) which puts his BMI now at 31.2.

He went from ‘Overweight’ to ‘Obese’ with no change in weight, just a shrinking height that often occurs as we age. By the way, he has always been muscular, so his BMI in the past was already incorrect in placing him in the ‘Overweight’ category in the first place.

Height and Weight Do Not Equal Body Fat Percentage

What the BMI does is dance around the core issue: body fat percentage. Knowing how overweight you might be, even if the BMI fits your body type, gender, age, etc., is irrelevant. The key is body fat percentage. The body mass index may correlate with body fat. However, it is a disservice to you to accept advice about BMI when these days it is so easy obtain your body fat percentage directly.

I’ve posted the concepts that make more sense in this regard, and what to do about getting the right information for tracking your body fat, here:

Body Fat Composition and Ideal Body Fat Percent

and here

Body Fat Percentage Using a Body Fat Monitor

By the way, measuring your body fat percentage, instead of relying on your body mass index, is easier than ever. Many large retail stores, local and online, offer bathroom scales that have bioelectrical impedance devices built in so you can read your body fat percentage at the same time you weigh yourself. They are usually inexpensive, in the 40 dollar range.

Recommendations

Use the body mass index as a first approximation of where you are physically. However, most certainly get a bioelectrical impedance monitor, handheld or in a bathroom scale, to keep track of what is really important. You may be surprised, if you by chance take some bad advice to diet by cutting out too many calories, by seeing your weight and BMI drop, while your body fat percentage stays the same or increases.

Here are the promised BMI lookup tables. Just take your BMI with a grain of salt, so to speak.

Good luck with your Body Mass Index,

Dr. D

Hi, this is Dr. Dennis Clark with my next installment on belly fat science based on the research that I’ve done in the medical literature on belly fat and how you get it and how to get rid of it. Today I want to talk about something that is kind of overlooked and conceptually it’s oversimplified quite a bit and that is the importance of weight loss. I’m going to say that, yes, weight loss is important. However, weight, the physicists tell me, is a function of gravity. That means that if you were in outer space you wouldn’t weigh anything. However, what component that is more important than weight is your body fat composition. If you weigh 200 pounds on Earth and you went to the moon, you’d weigh more like 42 pounds. However, on Earth if you were 35 or 40 percent body fat and went to the moon you’d still be 35 or 40 percent body fat. These are crucial kinds of information that will help you decide or help you find whether you are making progress on changing your weight and changing your health. It has to do with body fat composition. There are easy ways for you to measure your body fat composition. There are simple devices that you get in your bathroom scale at places like Costco or other discount membership clubs. The key is not to lose weight. I want to emphasize that. The key is not to lose weight. The key is to lose body fat. Drop that body fat percent and everything else will work a lot better. It shouldn’t surprise you that losing weight is not as important as you thought it would be. Losing fat is the key for long term health and body composition management that you really want to target. You can find out more about the importance of this and how to achieve it in my free belly fat book, which you can download now at BellyFatScience.com.

All the best with getting rid of fat,

Dr. D

The most effective and by far the most accurate way to measure your body fat percentage is to use a body fat monitor. If you are serious about weight loss then a good body fat monitor is essential and will measure your body fat to within 0.1% of the actual total.

When someone says they want to lose weight, what they actually mean is they want to lose body fat; of course every human needs a certain amount of fat as it is essential for correct bodily function. Fat regulates body temperature, cushions and insulates organs and tissues and is the main form of the body’s energy storage. However, too much body fat, especially visceral fat around the major organs, can cause wide spread problems such as heart disease, diabetes and strokes.

It is also a fact that women do carry more body fat than men; this is natural and means that a woman’s body naturally has a higher percentage of body fat than the body of a man. The percentage of essential body fat in a typical women’s body is between 10-12% whereas a man’s body contains only around between 2-4%.

Including our essential fat it is considered acceptable to have a total body fat content of between 25-31% for a woman and between 18-25% for a man. Anything above these figures and you would be considered to be both obese and having too much total body fat given the overall composition of your body.

When undertaking a weight loss program it is important to monitor body fat as this is a realistic indicator of your progress and if the diet is working for you. Remember, weight loss doesn’t always mean fat loss, yet fat loss should be the main aim of any weight loss or healthy diet regime. Many people often make the mistake of setting themselves impossible goals when they embark on a weight loss programme and lean body mass is not taken into consideration when setting yourself an ideal target weight.

By using a body fat monitor you can assess your exact requirements and achieve realistic goals. Judging exactly how much body fat you need to lose rather than how much weight is vital and this will lead to the maintenance of essential lean body mass which usually means calorie-burning muscle.

Body fat monitors use Bioelectrical Impedance Analysis, which involves sending a very low electrical signal through the body. This offers an indirect measurement of body composition. A safe electrical signal (50Khz, 800 microamps) is sent through the body via contact points (hands or feet)

Bioelectrical Impedance Analysis is based on the fact that lean muscle tissue contains high levels of water and electrolytes, and therefore acts as a conductor of an electrical signal. Fat mass is comparatively anhydrous and acts as a resistor to the flow of an electrical signal. Increasing levels of fat mass result in a higher impedance value, and correspond to higher levels of body fat.

Where to Get a Body Fat Monitor

Several online sources make getting your own device simple and inexpensive. EBay auctions offer many handheld devices made by Omron, which is what I own. You can also find the same devices on Amazon and other online superstores. The typical cost should be around $40 to $50.

Body fat percentage updates,

Dr. D

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Weight is a function of gravity. Yup, scientists know this and most other people do not. What this means is that you can be weightless in the absence of gravity.

However, no matter where you are in the universe, your body will have some fat. If you have a 30% body fat composition on Earth, you will have the same percentage on the moon. Okay, this may be a fun way to look at this topic. However, when it comes to weight loss vs fat loss, pay close attention.

The following article does a great job explaining what is important, what you body optimum should be, and how to get your own body fat measured:

The Importance of Losing Fat vs Losing Weight:

Did you know… That two people can have the same height and weight, but very different percentages of body fat?

Did you know… That as we age, we tend to gain fat around our organs (“visceral fat”) that can’t be detected by measuring “skin folds” or even with a scale?

Did you know… That chances are that if you are losing weight, you will lose muscle as well as fat?

READ MORE HERE…

All About Fat

The bottom line is that your health and fitness depend on keeping your body fat composition in an ideal range. Beware of any weight loss strategy that does not specifically address body fat loss.

All the best in natural health,

Dr. D

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