1. A method of using dual-energy absorptiometry to determine an estimate of visceral fat in a body and using said estimate, said method comprising the steps of: positioning a patient in a dual-energy absorptiometry system and operating the system to derive x-ray measurements for respective pixel positions related to a two-dimensional projection image of a body slice of the patient containing said visceral fat as well as subcutaneous fat; wherein at least some of said x-ray measurements are dual-energy x-ray measurements; computer-processing, through an automated process, said x-ray measurements to derive an estimate of said visceral fat content, Fat v , in said body slice, including estimating: (a) an area α t of said body slice parallel to a plane of propagation of x-rays for deriving said x-ray measurements, (b) an area α v of a portion of said body slice containing visceral fat (c) a total fat content, M t (Fat), of said body slice (d) an area α s of subcutaneous ha in said body slice, and (e) said visceral fat content Fat v in said body slice approximated as Fat v =(M t Fat)−α s wp s ) where w is an estimate of a thickness of the body slice and p s is an estimate of density of fat; wherein each of said areas α t , α v and α s comprises at least one or more ellipses wherein each of said ellipses comprises a major and a minor axis; using the x-ray measurements to estimate subcutaneous fat in x-ray paths from a source individually for a number of the pixel positions, and using the estimates of subcutaneous fat for estimating visceral fat in selected partial regions of the body slice; and displaying said estimate of visceral fat for use in medical analysis.