Stuart Wasser MD    Rockville Centre NY            516 594-2514 

What is an optimal weight?


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How much should we weigh?  Different people will have different answers. A model should weigh so much, a football lineman should weigh a bit more.  Clearly, many people are focused on looks;  they would  say that optimal weight is that weight in which our appearance is best.  However, as you know, appearance can be cultural and many people resort to unhealthy behavior to look good.

From my perspective, the healthiest weight should be that weight which promotes the longest life expectancies with the minimum amount of disease.  So how do we determine this?

Body mass index is one way of correcting weight for height.  It was initially described in the 1800s and than rediscovered in 1971 as a good way to measure "fatness) in a population.  The formula is as below:

                                                        
\mathrm{BMI} = \frac{\mbox{mass} \ \mbox{(kg)}}{\left( \mbox{height}(\mathrm{m})\right)^2}                                               Click for BMI Calculator

\mathrm{BMI} = \frac{\mbox{mass} \ \mathrm{(lb)} \times 703}{\left(\mbox{height} (\mathrm{in})\right)^2}

     

Unfortunately, the BMI was never intended to be applied to individuals because it makes no allowance for muscle mass, chronic disease or differences between men and women.  It also overestimates fatness in taller people.  

One of the reasons BMI  was adopted was that it ws shown to predict increased risk of diabetes, heart disease and dying. .  Originally optimal weight was originally defined as a BMI of under 27-28 by the NIH.  That was lowered in the 1990s to 25.  There was some studies that showed an increased risk health problems with a BMI of >25.  However, more recently. a studied failed to find increased heart disease when it compared a population of people, whose BMIs were 25-29,  to those who's BMI was under 25.  In fact, in the heavier group, the incidence of disease was 7% less.  It may be that the normal weight group had more people who suffered from chronic inflammatory medical conditions.  Nevertheless, the results do not clearly present a strong argument that BMIs of 25-29 are associated with health problems. 

Obesity may not have the same risk that is did for prior generations.  People living today have had different environmental exposures than our parents and grandparents did.  We did not live through the depression or dustbowl; food distribution and preservation is more reliable.  For these reasons,  more people today have never known hunger.  Evidence has shown that early life deprivations sets up long term changes in metabolism.  Once we begin to eat again, weight normalizes but diseases becomes more common.  The  diseases include diabetes and atherosclerosis.  

The point I am trying to make is that the consequences of obesity may be different for us than it was for prior generations.  Mild elevations in BMI do not mean we are unhealthy. 

I feel that the current  BMI cut-off level is too low.  The number should be higher; perhaps around the original value of 27-28.  However, even if a person has a slightly higher BMI, I would still consider them healthy and at a good weight as long as they are active and eating right.  

Another way of  determining obesity risk is to try to determine abdodominal fat.  Abdominal fat is more metabolically active than body fat.  It correlates more with the risk of disease.  One can simply measure the waistline.  Men should be less than 40 inches, woman should be less than 35 inches.  When examining persons whose BMI is 25-35, larger waistlines mean more risk of disease.  In patients whose BMI is greater than 35, the increased girth has little significance.  In this group, larger waistlines mean more abdominal fat and more risk of disease,

Another way of measuring abdominal fat is to determine the ratio of the sizes of waist to hip.  It is obtained by measuring the waist just above the naval and comparing that to the circumference around the hip/buttock area.  Men should be less than 0.95 - 1.0 (different experts say different things) and women should be less than 0.8-0.85.  Risk of disease goes up after these ratios are exceeded. 

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