3D body scanner reliably estimates body fat percentage across menstrual cycle phases

Body water changes across the menstrual cycle may affect body circumferences measured by a 3D body scanner, impacting estimated body fat percentage and enrollment into the Army body composition program. This study determined body scanner estimated changes in body fat across the menstrual cycle compared to the Army body circumference equation estimation and the resultant enrollment in the Army body composition program. Fifteen naturally menstruating females (age: 28±7 y, body mass: 58.4±5.4 kg) completed 3 morning laboratory visits, each during a different phase in the menstrual cycle (early follicular (EF), late follicular (LF), and mid-luteal (ML)). Phases were tracked using a home urinary hormone kit measuring luteinizing hormone, estrogen, and progesterone. Participants followed body scanner pre-test instructions regarding hydration, diet, caffeine, and exercise. A 3D body scanner estimated body fat and measured abdomen circumference, with the latter entered into the Army circumference equation to estimate body fat percentage. Army body composition program enrollment was determined when a body fat threshold was exceeded (age: 17-20 y: ≥30%, 21-27 y: ≥32%, 28-39 y: ≥34%, ≥40 y: ≥36%). Mixed model ANOVA and paired t-tests compared body composition measures across menstrual cycle phases. Chi square analysis compared enrollment into the body composition program across menstrual cycle phases. The body scanner estimated no differences in body fat across EF (28.1±3.2%), LF (28.9±4.1%), and ML (28.3±3.7%) (all p >0.05). Abdominal circumference was not different across EF (33.3±1.9 cm), LF (33.7±2.6 cm), and ML (33.0±2.3 cm) (all p >0.05), resulting in no difference in Army circumference equation estimated body fat across phases (EF: 31.2±2.3%, LF: 31.8±3.1%, ML: 30.8±2.8%, all p >0.05). The Army circumference equation estimation exceeded the body scanner estimation in all phases (all p≤0.01). There was no statistical difference in the proportion of participants enrolled into the body composition program across menstrual cycle phases with the body scanner (p=0.45) or Army circumference equation (p=0.43). However, the body scanner classified 20% (3/15) of participants differently depending on menstrual cycle phase, enrolling into the body composition program only during LF (N=2) or only during ML (N=1). The Army circumference equation resulted 33% (5/15) of participants classified differently depending on menstrual cycle phase. The 3D body scanner is reliable in estimating body fat percentage across menstrual cycle phases, however, some females close to the Army body composition program threshold were differently categorized throughout the month. 3D body fat measurements cannot directly replace Army equation estimations, as the Army equation resulted in a higher estimation of body fat compared to a 3D body scanner. Funding is provided through the Medical Technology Enterprise Consortium (W81XWH-22-9-0014).The views expressed are those of the authors and do not reflect the official policy of the U.S. Government, Department of the Army, or Department of Defense. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.