How is the measurement of body fat affected by having small breasts? What should my body fat be?

Answer: A woman with small or almost no breasts will have a lower body fat than one with large breasts, if all other things are equal, because breasts are at least 80% fat. Your body fat should fall within a healthy range (less than 32%), and beyond that it is a cosmetic and lifestyle issue.

More Info
Many women use body fat percentages to gauge the success of a diet program. Body fat measurements are useful as a way to measure change over time.  If a woman begins a program with very small breasts, she will likely have small breasts throughout the duration of her program, which makes the use of body fat measurements acceptable for tracking her progress. Keep in mind body fat tests are never perfect, but most are directionally correct and therefore effective in informing you if you are losing or gaining fat. The test will be a little inaccurate, however, because the equations to compute body fat from skinfold measurements, bioimpedance or underwater weighing assume an average size breast. Breast size varies significantly between women, but usually totals between one and two pounds. This is not a large amount of mass and does not contribute much to energy expenditure for a nonpregnant, nonlactating woman because of the fat content.  For what it’s worth, the average woman gains almost a pound in breast tissue during pregnancy.

How much will the measurement be off?
If a woman has very small breasts, it will not affect the actual body fat much more than a percent or two. If we use 2 pounds for the average woman in the body fat equations and we measure a woman with very small breasts, the formulas would incorrectly assume she had 2 pounds of body fat as breasts. For a female at 140 lbs and 25% body fat, 35 lbs is assumed to be body fat and 105 is lean tissue. If the small breasted woman has about 2 lbs of additional lean tissue in place of breasts, then she has 107 lbs of lean tissue and 33 lbs of fat. This would be about a one percent difference in body fat.

Once in a while a woman with breast implants wants to know how much weight to subtract from her scale weight to account for the implant weight. An easy way estimate the weight of implants is to add the volume from both sides and treat it as if it were water (the density of saline is close to that of water). For example, a woman with two implants both at 375 cc would have 750 cc total. If this were water, it would weigh 750 grams or (at 454g per pound) 1.6 lbs (1lb 10 oz).

What’s a healthy body fat for a female?
What a woman’s body fat should be depends on the perspective. Is the goal to improved health or athletic performance? Is it to look better? A healthy Body Mass Index (BMI), which is a way to compute height for weight, is between 19 and 25. A healthy body fat for a woman is less than 32%.