Are overweight people able to judge their ideal weight as well as non-overweight people?
The answer is Yes, as explained below. Be patient, it takes a little explaining...
The chart below shows adult Mens "Peoples Choice Ideal BMI" on the top line, using data from the Crawford and Campbell study. The bottom line uses "Normal" persons data ( of older Boys and Men from the NHANES III dataset2, using the median body weight at each increment of height) , and applies the well-established formula1 for "Lean Body Mass" to this data. Then, the lean body weight plus the height, is used to calculate the "Lean BMI" (kg/m2). This is plotted as the bottom line on the chart. The slopes are identical ( 0.5 ). The gap between "Lean" and "Ideal" mostly represents a desirable amount of body fat.
Since the lines are parallel (with identical slopes), it indicates that, as weight increases, people are able to judge their ideal weight to be proportional to their lean body weight. Whether a person is overweight, normal, or underweight, they seem to be able to choose an proportionate amount of fat, (above their lean body mass) to create their ideal weight. Analysis of female data has similar results.
It therefore appears reasonable to use the "People Choice Ideal BMI" to set an initial weight loss goal in overweight people.
Why do Men and Women have different ideas of ideal weight?
As this chart shows, Men's choice of Ideal Weight is higher than Women's, by about 2.06 BMI units. Why is that, you ask?
Does this gap between men and women represent physiology, or are societal factors responsible?
It is well known that average men have more skeletal muscle than average women, and average women have more fat than average men. Since muscle weighs more than fat, it is natural that men would have a higher overall BMI than women. The Lean Body Mass formulas1 for women and men show this. In the chart below, NHANES III data2 for males and females ( using median weight at increments of height) is plotted as Lean BMI. The average difference in lean body mass between males and females is 1.76 BMI units.
Comparing the gaps between Men and Women, of People Choice Ideal BMI versus Lean BMI, the difference of 2.06 minus 1.76 is 0.3 kg/m2. This translates into an approximate weight difference of only 2 pounds, which indicates that lean body composition differences between Men and Women explains most of the difference between Men and Women's perceived People Choice Ideal Weights.
In other words, societal pressures ( media, advertising, peer-pressure, etc) seem to have little influence in how Men and Women perceive their Ideal Weight, which is reassuring.
References
- Formulas for Lean Body Weight (men) = (1.10 x Weight(kg))
- 128 ( Weight2/(100 x Height(m))2)
Lean Body Weight (women) = (1.07 x Weight(kg)) - 148 ( Weight2/(100 x Height(m))2) - NHANES III. Third National Health and Nutrition Examination Survey. 1988-1994 data from USA.
Back to Ideal Weight Calculator, or the Body Mass Index calculator. Last edited 26-May-2008. Copyright
