BMI vs Body Fat %

The amount of body fat a person should have depends upon a few variables. Women typically have more body fat than men. Breasts are almost all fat, and women have more fat around their hips. Women with a body fat percentage that is too low will experience chronic fatigue, weakened bones, a disordered metabolism, absent periods, and an inability to concentrate. 

Another factor is age. As people get older, their muscles tend to shrink, and they tend to accumulate visceral fat. This is at least partially related to the decline in testosterone and other hormones. 

It is important not to confuse BMI with body fat. The BMI (body mass index) numbers are NOT percentages of body fat. You may see advice on web sites.  The difference of the two can be confusing.  For example, a BMI of 29 is in the overweight range for women. This has nothing to do with 29 percent body fat.

Age-Adusted Body Fat Percentage Recommendations Women Age              Underfat  Healthy Range    Overweight   Obese 20-40 yrs        Under 21%        21-33%   33-39%   Over 39% 41-60 yrs        Under 23%        23-35%   35-40%   Over 40% 61-79 yrs        Under 24%        24-36%   36-42%   Over 42% Men Age      Underfat         Healthy Range    Overweight       Obese 20-40 yrs        Under 8%                  8-19%    19-25%   Over 25% 41-60 yrs        Under 11%        11-22%   22-27%   Over 27% 61-79 yrs        Under 13%        13-25%   25-30%   Over 30% Source: Gallagher et al. Am J Clin Nut 2000; 72:694-701

Andersen, JL; Schjerling, P; Saltin, B. Muscle, Genes and Athletic Performance. Scientific American. 9/2000 Thayer R, Collins J, Noble EG, Taylor AW. A decade of aerobic endurance training: histological evidence for fiber type transformation. Journal of Sports Medicine & Phys Fitness. 2000 Dec;40(4).