From the RDs - a word on "ideal" body weight

We have read multiple posts regarding the practice of adjusting body weight in order to determine how many calories, how much fluid, how much protein, etc. a person pre or post-op WLS should use as a goal.  We thought you might enjoy knowing a little more about this practice - and some of the controversy surrounding it. Enjoy and feel free to share!

What is an adjusted body weight after all?

           The history of trying to find out what people “should” weigh goes back over a century.  The first formula (that I could find) was devised in 1871 by a Dr. Broca in France; it was later translated into a formula that became known as “Broca’s Index”

           The formula:      For women allow 100 lbs for the first 5 ft. and 5 lbs for each additional inch.

     For men, allow 110 lbs for the first 5 ft., and 5 lbs for each additional inch.

           In the 1940’s, ideal weight was looked at one more time - the Metropolitan Life Insurance Company made a table of “ideal” body weights for height, based upon a survey of their customers and to assist with calculating health risks.  These became known as the Met Life Tables - they have been updated a few times since then, but they are still in use.

           In 1964, a physician by the name of Hamwi suggested a method for ideal body weight (IBW) calculation in an American Diabetes Association publication.  His formula is very similar to Broca’s and is:

           Male IBW:     106 lbs for the first 5 feet, and 6 lbs per inch over 5 feet

           Female IBW: 100 lbs for the first 5 feet and 5 lbs per inch over 5 feet

 In the US, this is by far the most widely used formula amongst dietitians.

           In 1974, Dr BJ Devine published a formula for ideal weight, which basically took the Broca Index and translated it into metric weight.  This formula became known as the Devine Formula and is:

   Males:    IBW in Kg = 50 Kg + 2.3 Kg for every inch over 5 feet

  Females:  IBW in Kg = 45.5 Kg + 2.3 Kg for every per inch over 5 feet

 As this formula was used for medication dosing, it soon became the most commonly used formula for ideal body weight.  To this day it is still the most widely used formula worldwide.  

 

 

 

 

 

 

 

 

 

 

 

 

 

The battle waged on…

 In 1983 Dr. JD Robinson published his formula for IBW and is:

   Males:           IBW in Kg = 52 Kg + 1.9 Kg per inch over 5 feet

   Females:       IBW in Kg = 49 Kg + 1.7 Kg per inch over 5 feet

 And Dr. Miller’s formula, also in 1983 is:

 Males:           IBW in Kg = 56.2 Kg + 1.41 Kg per inch over 5 feet

 Females:       IBW in Kg = 53.1 Kg + 1.36 Kg per inch over 5 feet

           In 2000, the Annals of Pharmacotherapy published an article to put in perspective the origins of the “ideal body weight” formulas and to further define the formulas by trying to figure out if they were devised to measure “fat-free mass” and could represent “lean body weight” or muscle mass.

 

 

 

 

 

 

 

So we have all of this information on ways you can calculate an “ideal weight” - but people still found flaws in the various formulas and further adjusted them.  It is difficult to find the specific research, but practice methods have taken the IBW formulas into many different places. For example:

 For frame size - (use your favorite calculation)  To account for small frame size, take IBW and subtract 10%

 To account for large frame size, take IBW and add 10%

 For weight range- (use your favorite calculation)  Take IBW x .90 to get the low acceptable body weight

 Take IBW x 1.1 to get the highest acceptable body weight

 For Obesity - (use your favorite calculation)

 Take IBW + total body weight - IBW (x .25) = adjusted body weight (assumes fat tissue is 25% metabolically active)

 OR

  Take IBW + total body weight - IBW) x .40) + adjusted body weight(assumes fat tissue is 40% metabolically active)

           And just to complicate things further, in recent years more data has emerged comparing these many formulas to Body Mass Index (BMI).  Most compared poorly, especially for short females who would have an ideal weight in the range equivalent to a BMI of 19.  Note also that none of these formulas take into consideration age, race, hydration status, osteoporosis, muscle mass, etc. - just gender and height.

 Now think about the fact that these flawed formulas are being used to calculate how many calories you should eat, how much fluid you should take in, how many calories you are burning…

 In multiple studies, use of adjusted body weights resulted in less accuracy than using actual weight for studies of energy needs - these studies are important because we can objectively measure energy expenditure using indirect calorimetry.

           It must be recognized that everyone trained in dietetics or nutrition was taught to use these formulas.  They give you a place to start, a goal to shoot for.  What unfortunately happens in practice is that these calculated weights become the “law” and practitioners promote them unwaveringly.  A calculated “ideal” makes sense -  but making every plan for hydration, energy, protein, etc. contingent on this calculation is irresponsible.

           What makes more sense is using these “ideals” as a place to start.  For most calculations of energy, protein, and fluid using a patients real weight is more accurate.  Sure, you may dial down the calories to promote weight loss, but don’t do the same with protein and fluid!  If a person is losing weight, they need more water - not less!  This is to flush out the waste products of metabolism.  For protein, many obese people are protein deficient.  If a protein intake goal is set too low, they will not have the ability to heal quickly, will have impaired immune function, and will suffer from the body “stealing” from its own tissue (usually the organs and muscles which are needed for ‘other’ things).

 The bottom line is - adjusting body weight has its place in nutrition assessment, but it should not be used for all recommendations.  We have a responsibility to treat the person in front of us, not the adjusted, calculated equation on a piece of paper.

 As Winston Churchill said, “However beautiful the strategy, you should occasionally look at the results.”

 And our ultimate responsibility “Primum non nocere” - First do no harm. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

here i was feelin thin until i did the calculation and i'm at the highest acceptable body weight (137) for my height (5'5). i prefer this site http://www.halls.md/body-mass-index/bmi.htm whi*****ludes age ~ according to it i'm in th 16th percentile.

I hope the message that "ideal body weight" has many different meanings and applications is given some consideration.  Looking at the site you referenced, Dr Halls offers the following:

Above all, Don't Worry, Be Happy.  It's unhealthy to have anxiety over a less-than-perfect body image.  And, if this calculator's description of your body seems wrong for you, just trust your own judgment.  A healthy mental attitude is just as important as physical fitness. The same message can be applied to energy calculations based on IBW, fluid recommendations based on IBW, or protein recommendations based on IBW.  If it doesn't seem right for you, do a little research, and trust your own judgement. This thread has had a lot of "views" - I hope it gets a lot of people thinking too!

Yeah, I'm 5'5" as well and the formulas say 125-137... which is totally ridiculous!  I've weighed that little in my life... at 133 (smack in the middle) I looked disgustingly emaciated. You could see all my veins, muscles and connective tissue. I looked like a refugee, my hair was thin, my skin was dry and my period was all messed up. When I went to my doc and he ran electrical impedence test on me... it turned out I had less than 6% body fat.... way too low for a woman, almost too low for a man. Ever since, IBW charts and BMI charts are just a loose goal and I shoot for the "large frame" or "top of the range"... but rely on electrical impedence to determine my body composition because that's what's really important, not just your weight... cuz, hey, muscle weighs much more than fat.

i'm with u ~   i cant even imagine myself at 125, my family already thinks i'm too thin.  altho i dont agree with too thin, i do think i'm as low as i should go.  my goal now is to maintain, something i've neva been able to do before. i see that u recently had surgery, i wish u well on ur journey~

Hi Ladies,  Keep in mind that these calculations are based on a wide range of "average" people. What exactly is average??? Everyone is different and unique. As a group (dietitians) it's important to have baseline calculations so we can be consistent with our recommendations. The benefit of visiting a dietitian is personalized, individual recommendations. We take into account that frames, muscle mass and bone denisty vary from person to person. Please don't let these calculations get you down. We really were just trying to give some background of where and why they came about.  Again, everyone is unique and the bottom line is where one feels healthy and strong. Too often we get caught up on numbers or sizes rather than a point where we feel GREAT (inside and out)!!   Keep up the good work!