BMI Isn’t Very Helpful, but What’s the Alternative?

December 27, 2022

I hate BMI.

BMI, or body mass index, is a simple formula with a difficult relationship with modern medicine. It only takes height and weight into account to categorize individuals as either healthy or unhealthy. The only institutions that still rely on BMI are insurance companies, which charge higher premiums for people categorized as “unhealthy” by their BMI.

As a physician, I would never make a medical decision based on someone’s BMI, and would greatly encourage the widespread acceptance of a BMI alternative.

Here’s what you need to know.

Why Do We Need a BMI Alternative?

Why do we need a BMI alternative? Well, for starters, BMI was created in the 1830s — yes, that long ago!

Medicine and technology have changed a lot in 200 years, and so has the average human. Our body compositions have changed, and so has our health.

Back in the 1800s, people were generally underweight. People weren’t getting the nutrition or quantity of food they needed to thrive. When the BMI metric was designed, it was very rare to see people who were overweight.

By comparison, in today’s America, almost everybody is categorized as overweight. We’re very different from the people the BMI was designed to help.

BMI is obviously outdated, and hardly tells us anything. We know now that weight and height alone are not enough to categorize someone as healthy.

An obvious example of BMI’s shortcomings is in the case of bodybuilders. These people have almost no body fat and are nearly 100% muscle, but by BMI standards, they are morbidly obese. Obviously, these people are far from unhealthy, but when they include their BMI on their life insurance paperwork, they get charged much higher rates.

BMI also doesn’t differentiate between men and women. Fundamentally, women need more adipose tissue than men do. This fat distribution protects against certain metabolic diseases, like type II diabetes, and is completely normal and healthy.

Putting men and women into the same category for standards of body fat is a horrible idea. I’m not sure if they knew this in the 1800s, but we definitely know it now.

The Difference Between BMI and Alternative Measurements

It’s pretty easy to calculate BMI: it’s a person’s weight in kilograms divided by their height in meters squared.

But calculating this number isn’t intuitive. Yes, there are apps and websites that can calculate it for you, but the scale of these BMI scores is still arbitrary. The cutoffs for normal and abnormal weight are based on outdated population averages.

As a BMI alternative, compare BMI with a bioimpedance value.

Bioelectrical Impedance Analysis measures exactly how much fat and muscle you have on your body. When you get this reading, you’re getting a specific value about your actual health, not just a metric from aggregated population data.

Infographic: BMI Isn’t Very Helpful but What’s the Alternative?

This test gives an extremely detailed overview of your body’s composition. It measures your:

  • Muscle mass: A great predictor of your quality of life down the road. How strong you are indirectly correlates to how healthy you are. Declining muscle mass in a man could be a sign of low testosterone, and an increase in muscle mass can provide positive feedback that the work you’re putting in is producing results. Building muscle generally lowers blood sugar — the more muscle mass you have, the less likely you are to be diabetic.
  • Percentage of body fat: In the last 15 years, we’ve learned that adipose tissue is metabolically active — that is, your fat tissue actually secretes hormones. Too much fat and hormone secretion can upset the equilibrium of your body, so knowing how much fat you’re actually carrying is very helpful.
  • Basal metabolic rate: How many calories you burn every day at rest. It may be tough to believe, but just lying in bed will burn a certain amount of calories. Let’s assume you do zero activity — you’ll likely still burn a surprising 1,400 to 1,600 calories a day. On top of that, most people burn an additional 300–500 calories just by doing normal, everyday activities. If your basal metabolic rate is extremely unusual, it can be an indicator of other diseases.
  • Total fat mass: Simply put, your total fat mass is how many pounds of fat you have. This can be a wake-up call for patients who are overweight — saying someone carries 50 pounds of fat has more of an impact than saying they have 30% body fat, since it’s easier to think in pounds rather than percentages.
  • Visceral fat: Perhaps the most important data point from a physician’s perspective, visceral fat is what surrounds your organs. I’m interested in a patient’s visceral fat report because it’s the best long-term predictor of cardiovascular disease. It also helps me predict internal abdominal cancers of the colon, liver, and pancreas. Visceral fat and percent body fat don’t necessarily coordinate — you can lose a ton of body fat and not lose any visceral fat.

What’s the Flaw of Bioimpedance?

The challenge with bioimpedance readings is that fluids are counted as fat. If you drink a bottle of water or have a full bladder before your test, it’s going to say you have more body fat than you actually do.

I would never advocate for dehydration, but getting your body composition measured when you’re on the dryer side of the hydration scale is better. For this reason, if you’re measured first thing in the morning, you’ll get a more accurate reading than if you’re measured in the afternoon.

How Can You Get Your First Body Composition Report?

The best way to measure your bioimpedance is to find a machine designed for it.

There are two types: two- and four-point lead machines. Some gyms have two-point machines that you stand on, or they have two bars on the wall that you grab to complete the electrical circuit.

These two-point machines can give you a general ballpark for your report, but they’re not as accurate as a four-point lead. Generally, the more points of contact with the machine, the better. At our offices, we use the four-point InBody Body Comp Analysis, which is much more accurate.

All of our patients use the machine at least once a year during their annual physical, but they can also use it whenever they want an updated reading. They don’t need to come in and see a physician to use it, which is convenient for anyone who wants to check whether they’re losing or gaining weight. We want to make it as easy as possible for people to get a report that makes a difference!

Dr. Jonathan Schmidt

Dr. Schmidt is a board-certified family medicine physician with undergraduate degrees in Microbiology and medicine from Southern Illinois University and the University of Illinois. He completed his residency at St. Joseph Regional Medical Center in South Bend, IN and has a passion for putting his patients first in his practice. In his free time, Dr. Schmidt enjoys spending time with his family and participating in outdoor activities such as water sports and woodworking.

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