1. A dual energy x-ray absorptiometry (DXA) method for determining visceral fat of a selected sub-volume of a visceral fat volume of a patient, which visceral fat volume is surrounded by a subcutaneous fat volume and together therewith forms a total volume of a length of the patient's body, wherein the sub-volume also contains material that is not visceral fat, comprising: acquiring DXA measurements for respective pixel positions of a two-dimensional DXA projection image of said total volume, including measurements of the subcutaneous fat and the visceral fat in the total volume, thereby forming a two-dimensional DXA image showing the subcutaneous fat and visceral fat of the length of the patient's body; computer processing said DXA measurements as represented by said two-dimensional DXA image to determine therefrom differences between visceral and subcutaneous fat at least in a slice of the patient's body and an estimate of visceral fat contained in said sub-volume of the visceral fat volume that also contains material that is not visceral fat; and providing and displaying an indication of said visceral fat estimate.