Regional distribution of the body fat: use of image techniques as tools for nutritional diagnosis

Abstract

Fat mass is the most variable component in the human body, both when comparing several individuals and when considering changes in the same person throughout life. Obesity is characterized by an excess of body fat that affects health and well-being of individuals. Risk associated with excess body fat is due, in part, to location of fat rather than to total amount. Today is stated that causes and metabolic consequences of regional distribution of fat are of particular clinical importance. To identify a compartment of morbid adipose tissue and to be able to act on it is one of the main aims of the present research. In this review, we have revised the existing literature on location and characteristics of total body fat in human adult. We have focused on abdominal region, basing this review on the use of modern imaging techniques available nowadays, such as computerized tomography and magnetic resonance imaging, with their advantages and limitations. The purpose of this review is to assess whether it is possible to know the body composition and fat distribution on the basis of image methods. Computed tomography technique was first applied in studies of obesity, but today, due to the inconvenience of irradiating the patient, this technique is being replaced by magnetic resonance that, in addition to avoid radiation, provides images of extraordinary quality. Both methods allow to subdivide the classic general fat depots in others more specific. Subcutaneous fat depot can be superficial or deep, while visceral can be divided in mesenteric, omental or epiploic, retroperitoneal and perirrenal fat. In addition, these modern techniques of imaging permit to study muscular fat, considered by some authors as the new fat compartment. Muscular fat includes fat located between skeletal muscle fibers, called extramyocellular fat, as well as lipids located within skeletal muscle fibers (intramyocellular fat). Its importance lies not only in size, similar to visceral fat, but on its pathophysiological implications. Finally, techniques of image analysis have prove to be extremely useful in studying the location and extent of abdominal fat compartments, becoming reference to validate equations obtained from the so-called "indirect methods".