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Where Your Body Fat Estimate Comes From

Body Composition1 min readJackson & Pollock; Woolcott & Bergman

Every body fat method in Kriterion is a published equation, and each trades accuracy for how much you have to measure. Calipers at three sites (Jackson-Pollock) are the most accurate of the four if your technique is consistent, converting skinfold thickness to body density and then to a percentage via Siri's equation. The US Navy method needs only a tape measure at the neck and waist, plus hips for women, and is the standard used for military body composition assessment. Relative Fat Mass is newer and simpler still: height and waist only, derived by Woolcott and Bergman against DXA scans, and it outperforms estimates based on BMI, particularly for women.

The BMI method (Deurenberg) needs no measuring at all but is the least accurate, because it can't distinguish muscle from fat. None of them is a DXA scan. All of them are useful for tracking a direction of travel, which is what matters more than the absolute number.

How Kriterion uses this

Kriterion never quietly stores an estimate as though you had measured it — a figure you measured stays yours, and an estimated one is worked out fresh and labelled as an estimate.

References

  1. Jackson AS, Pollock ML. Generalized equations for predicting body density of men. British Journal of Nutrition, 1978.
  2. Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Medicine & Science in Sports & Exercise, 1980.
  3. Siri WE. Body composition from fluid spaces and density: analysis of methods. In: Techniques for Measuring Body Composition. National Academy of Sciences, 1961.
  4. Woolcott OO, Bergman RN. Relative fat mass (RFM) as a new estimator of whole-body fat percentage. Scientific Reports, 2018.
  5. Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British Journal of Nutrition, 1991.
  6. Hodgdon JA, Beckett MB. Prediction of percent body fat for US Navy men and women from body circumferences and height. Naval Health Research Center, 1984.

Kriterion is the app this reasoning is built into

It measures your maintenance calories from what you actually ate against what the scale actually did, tells you how firmly the number is pinned down, and checks its own past predictions against your results. Free logging, UK food data, and no ads.