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Are Normal-Weight Americans Over-Fat?



Readers of these pages will recall that I am not a fan of defining obesity based on BMI because this measure of “fatness” does not perform well when applied to individuals. Thus, people with identical BMI levels can have remarkably different levels of body fat (not to mention remarkable differences in their actual health status).

This, incidentally, is also true for people with BMI levels in the so-called “normal” range, a finding which prompted Marie-Pierre St-Onge from Columbia University, New York, to ask whether normal-weight Americans are perhaps “over-fat” (rather than overweight). Her commentary was just published online in OBESITY.

it has previously been suggested that a normal body fat level should be around 21ÔÇô32% for 21- to 39-year-old, normal-weight women and 8ÔÇô20% for men of the same age and BMI category.

However, a recent analyses of data from National Health and Nutrition Examination Surveys (NHANES) 1999ÔÇô2004, reported that the 5th percentile for body fat, which should represent the leanest of the US population, corresponds to 28 and 17% body fat for women and men, respectively.

Most disturbingly, the 50th percentile of body fat in the US population was as high as 41 and 28%, for women and men, respectively.

When categorized by BMI and age, the data also show high percent body fat values, particularly in lower BMI categories.

Thus, clearly, even normal-weight Americans appear to have more body fat than is considered “normal”.

This is an important finding, because “normal” BMI levels are generally interpreted as being “healthy”, meaning that no “weight-loss” intervention is recommended.

As I have pointed out before, BMI levels are limited in defining body-fat-related health, because an excess BMI alone does not necessarily reflect ill health.

On the other hand, it now seems that a normal BMI level does not necessarily reflect good health either, as a substantial number of people with normal BMI levels may well have excess body fat, which can potentially contribute to cardiometabolic and other “body-fat-related” health problems.

Perhaps, it is time for clinicians to turn to more accurate measures of body-composition when defining obesity rather than simply using the rather crude surrogate of BMI.

AMS
Edmonton, Alberta

St-Onge MP (2010). Are normal-weight americans over-fat? Obesity (Silver Spring, Md.), 18 (11), 2067-8 PMID: 20978478

Li C, Ford ES, Zhao G, Balluz LS, & Giles WH (2009). Estimates of body composition with dual-energy X-ray absorptiometry in adults. The American journal of clinical nutrition, 90 (6), 1457-65 PMID: 19812179

3 Comments

  1. I use bioelectrical impedence (the handheld unit) to determine fat/lean tissue values. I rarely see a correct correlation with fat and BMI, particularly in the aging population when sarcopenia is prevelant. Heavy dieters also have reduced lean tissue levels. I have also incorporated WC based on the amazing studies now centered on visceral adiposity as a risk factor to CVD and MO. As a practioner, I beleive we should add these components to get a better view of fat mass.

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  2. As a woman who’s in the BMI overweight range but in normal range (just barely, but there) for body fat percentage, I am really glad to read this. When I was younger and 20 pounds lighter, I was not as healthy and active as I am now, nor did I eat as well. I get really tired of body weight being seen as the be-all end-all arbiter of health.

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  3. I think this is something that needs to be looked at. As a nutrition student I had a DEXA scan done that said I was right in the normal range for body fatness for a 23 year old woman. This surprise me becasue at that time my BMI was 16.8. I certainly believed I was health and came from a family that was all tall and lean, but it was intereating to see DEXA said I had a normal body fatness when most people would tell me to gain weight.

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