Implementation of an overnight fast is a pervasive recommendation prior to body composition assessment, but this is not always feasible. Previous research has indicated that for dual-energy X-ray absorptiometry (DXA) scans, the trunk region may be particularly susceptible to biological error induced by food and fluid intake. This analysis explored the potential utility of excluding the trunk region from nonfasted DXA scans. Recreationally active adults were assessed by DXA after an overnight fast and again after consumption of standardized high-carbohydrate and low-carbohydrate diets. The effects of food consumption on total and appendicular lean soft tissue (LST; ALST) and ALST-derived skeletal muscle mass (SMM) were evaluated via analysis of variance, and metrics of reliability were calculated. In both conditions, the constant error of nonfasted assessments was slightly lower when the trunk was excluded (ALST and SMM: 0.7–1.2%; LST: 1.5%). However, in both conditions, the total error, standard error of the estimate, and limits of agreement were higher for ALST and SMM (total error: 2.4–3.0%; standard error of the estimate: 2.2–2.8%; and limits of agreement: 4.5–5.6%) than LST (total error: 2.1%; standard error of the estimate: 1.3–1.4%; and limits of agreement: 2.5–2.8%) when expressed relative to mean values. The added technical error due to demarcation of body regions for ALST and SMM appears to outweigh the removal of biological error due to exclusion of the trunk. Although elimination of the trunk region is theoretically appealing for nonfasted DXA assessments, it is apparently an inferior method compared with utilizing whole-body LST.
Grant M. Tinsley and Brett S. Nickerson
Grant M. Tinsley and Darryn S. Willoughby
Low-carbohydrate and very-low-carbohydrate diets are often used as weight-loss strategies by exercising individuals and athletes. Very-low-carbohydrate diets can lead to a state of ketosis, in which the concentration of blood ketones (acetoacetate, 3-β-hydroxybutyrate, and acetone) increases as a result of increased fatty acid breakdown and activity of ketogenic enzymes. A potential concern of these ketogenic diets, as with other weight-loss diets, is the potential loss of fat-free mass (e.g., skeletal muscle). On examination of the literature, the majority of studies report decreases in fat-free mass in individuals following a ketogenic diet. However, some confounding factors exist, such as the use of aggressive weight-loss diets and potential concerns with fat-free mass measurement. A limited number of studies have examined combining resistance training with ketogenic diets, and further research is needed to determine whether resistance training can effectively slow or stop the loss of fat-free mass typically seen in individuals following a ketogenic diet. Mechanisms underlying the effects of a ketogenic diet on fat-free mass and the results of implementing exercise interventions in combination with this diet should also be examined.