What should you weigh? A look at Ideal Body Weight

With the physique of Mr. Salty, the pretzel guy, I am the rare person who hasn’t spent a single moment of my life wondering about how much extra weight I am carrying.

Since “What should I weigh?” is a very common refrain in our high-calorie, low-activity culture, you’d think someone would have figured out the answer to that question a long time ago.  But it’s not been easy. Humans come in all different heights, shapes, frame sizes, and compositions, befuddling our attempts to find a “one-size-fits-all” equation.

Actuaries at life insurance companies were the first to give it a try, creating height-weight tables to better understand their customers’ individual mortality risk. These tables were used to define what became termed as a “desirable” or “ideal” body weight. In the mid-1970’s, the data from various life insurance tables were found to be generally consistent with the following equation:

Ideal Body Weight, men: 106 lbs + 6 lbs for every inch over 5 feet

Ideal Body Weight, women: 100 lbs + 5 lbs for every inch over 5 feet

Some experts suggest adding an additional 10% to the total if you’ve got a large frame, and subtracting 10% if you have a small frame.

If you find even the simplest math to be a challenge, the website MDCalc can “calc” it for you.  Under the “When to Use” tab, the page’s purported author, Dr. Manjunath Pai, suggests that for shorter individuals, a common practice is to subtract 2-5 pounds for every inch under 5 feet. So, for example, a 4’10” person would subtract 4-10 pounds from 100 (female) or 106 (male).

Although MDCalc credits Dr. Pai as the creator of its IBW page, apparently, they’ve not been able to get a hold of him. Because in the area below the calculator, they ask “Are you Dr. Manjunath Pai? Send us a message to review your photo and bio, and find out how to submit Creator insights!”

I do hope they can connect. At the very least, MDCalc’s designating Pai as a “leading expert on the Ideal Body Weight” should be a conversation starter; unless Pai finds this to be utterly false and libelous, and then I don’t see any good coming of it. I suspect MDCalc is correct—Pai is indeed an IBW expert—by virtue of his having penned the article “The Origin of the ‘Ideal’ Body Weight Equations.”

The Ideal Body Weight (IBW) formula has its drawbacks (including that it underestimates IBW for shorter people, and overestimates IBW for taller people) and it’s been largely replaced by the more familiar Body Mass Index (BMI), which divides one’s weight in kilograms by the square of one’s height in meters.

Here are the BMI ranges:

<18.5 Underweight

18.5—24.9 Normal

25—29.9 Overweight

30—34.9 Obese

>35 Extremely obese

The problem with Body Mass Index (BMI) is that it can’t differentiate between what makes up “the mass.” Is it healthy stuff like muscle or a heavy bone structure, or is it unhealthy stuff like fat? That blind spot creates problems. For example, people with a heavier muscle mass will have a falsely elevated BMI. And older folks, who have a tendency to lose muscle and gain fat, will see their BMI remain the same despite that unhealthy exchange.  

In 2016, a group of researchers published an easy to use and highly accurate equation that allows users to see what their ideal body weight might be at any particular goal BMI.

Weight in pounds = 5 X BMI + (BMI/5 x (Height in inches – 60))

When I ran my own numbers through it, this equation seemed far more accurate, flexible, and useful than does the IBW equation.

Dr. Pai, if you’re still out there, please send me a message, so you can review this innovative formula and find out how to submit to craigbowronmd.com!