Serious Problems of Ideal Body Weight Formulas

February 16th, 2010 by Di Heap Leave a reply »

I’m back on track this month with regular workouts and following a well designed eating plan.  I have a goal weight in mind but when I looked back over the personalised plan I’m following I was horrified at the goal weight set for me:  52-70kg.

There’s a wide variation in those figures and at first glance it looks reasonable.  Many women would simply accept the goal, go hard-out in diet and exercise toward the lowest figure and then cry when they fail to reach the target.  Continued food deprivation and yo-yo diets can lead to morbid obesity and so worsen the situation the hapless person finds himself in.

So what’s wrong with that goal?

Simply, it fails to take into account ethnicity and muscle mass amongst other factors.  For me an eventual goal weight of 68-72 is attainable and healthy (and that’s the upper limit of the plan I am following).  The lower limit of 52kg is just too low and could deplete my muscle mass to a point where my bone density would lower putting me at risk of osteoporosis or easily breaking bones.  My metabolic rate would fall and with that my energy level and mental acuity.

My Personalised Eating Plan

The diet and exercise plan I’m using as a guide to plan my eating this year was written specifically for me by a highly respected nutritionist whose advice and articles I value.  It was based on my age, sex, height, weight, waist measurement, and my opinion of my body type which I entered as “muscular”.   The results that came back were fairy accurate compared with the results I get from the Body Composition Analyser machine at Vibra-Train where I work.  The estimated metabolic rate was lower than my actual rate but the BMI measurement was correct. (Note: BMI is another outdated measurement that fails in usefulness because off ethnicity and muscle mass differences).  The report said I am Obese based on my BMI (Body Mass Index).  It then gave dire warnings of health problems that accompany obesity.  These would be enough to scare anyone into eating better and exercising regularly and so are good for people to read although in my case, again they are overstated as my BMI does not reflect my real state.  I know my actual muscle mass percentage from the Body Composition Analyser machine and as it’s high it skews my BMI.

In a personalised diet plan where does the goal weight come from?

Many websites give “Ideal Body Weight” using arithmetic formula that was designed for medicine dosing, (NOT for weight control).  One such formula is that of Dr BJ Devine who in 1974 converted a formula already in use based on inches of height and pounds of bodyweight into metric figures.  It gives ideal (or expected) bodyweight as

Men: Ideal Body Weight (in kilograms) = 50 + 2.3 kg per inch over 5 feet.
Women: Ideal Body Weight (in kilograms) = 45.5 + 2.3 kg per inch over 5 feet.

These figures suggest a Body Mass Index of about 23 for adult men (this is rather high) and for adult women of 20.8 which for many women is too low and suggest an ideal body weight for most women seriously close to lean body weight (organs, bone, muscle, with no fat).

Although Devine’s formula was updated in 1983 by Dr JD Robinson and DR DM Miller, their formulas still have serious faults.  And even before the Devine IBW formula the insurance company, Metropolitan Life was, in 1943, using medical dosing weight formula to set height/weight tables.

The flaws in these formulas when used for Ideal or Best Body Weight are just too high to be used today.  Years ago on a battlefield or in a hospital when a person’s weight had to be calculated immediately to give dosage of life-saving medications (like theophylline, digoxin, gentomyin) these estimations or expected weight were invaluable but not so today.

What is your Real Ideal Weight?

My advice to women (and men) wanting to know their true ideal body weight is to be very wary of online formula and even ranges on a diet plan made for you.  Your ideal weight is the one at which you are feel well and are active. It’s the weight at which you feel at your best! You know what this is and a quick glance in the mirror shows if you are carrying muscle or fat.  A test using a Body Composition Analyser (a machine that uses a light electric current to take measurements) can be helpful as it gives a printout of your measurements including Body Fat Percentage and Muscle Mass Percentage and an overall fitness score, a starting point to work from and then a repeat test three – five months later to show your progress.  In Auckland Central there is a BCA machine at Vibra-Train, in Victoria St West.

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