Assessing the utility of cardiorespiratory fitness, visceral fat, and liver fat in predicting changes in insulin sensitivity beyond simple changes in body weight after exercise training in adolescents

Fat-free/lean body mass in children with insulin resistance or metabolic syndrome: a systematic review and meta-analysis

BACKGROUND

Lean / Fat Free Body Mass (LBM) is metabolically involved in active processes such as resting energy expenditure, glucose uptake, and myokine secretion. Nonetheless, its association with insulin sensitivity / resistance / glucose tolerance and metabolic syndrome remains unclear in childhood.

METHODS

The current investigation aimed to examine the differences in fat-free mass /lean body mass according to the presence of insulin sensitivity/insulin resistance/glucose tolerance/metabolic syndrome in children. A systematic search was carried out in Medline/PubMed, Embase, Scopus, Web of Science, and SciELO, covering the period from each database's respective start to 21 June 2021. Two researchers evaluated 7111 studies according to the inclusion criteria: original human studies, written in English or Spanish, evaluating fat-free mass/lean body mass in children and adolescents including both with and without insulin sensitivity/insulin resistance /glucose tolerance and metabolic syndrome and reported the differences between them in terms of fat free mass/lean body mass. The results of the studies were combined with insulin sensitivity, insulin, resistance, glucose tolerance and metabolic syndrome. The standardized mean difference (SMD) in each study was calculated and combined using the random-effects model. Heterogeneity between studies was tested using the index of heterogeneity (I2), leave-one-out sensitivity analyses were performed, and publication bias was assessed using the Egger and Begg tests.

RESULTS

Finally, 15 studies which compared groups defined according to different glucose homeostasis criteria or metabolic syndrome out of 103 eligible studies were included in this systematic review and 12 studies in the meta-analysis. Meta-analysis showed lower fat-free mass/lean body mass percentage in participants with insulin resistance/glucose tolerance/metabolic syndrome (SMD -0.47; 95% CI, - 0.62 to - 0.32) while in mass units (kg), higher values were found in the same group (SMD, 1.01; 95% CI, 0.43 to 1.60).

CONCLUSIONS

Our results identified lower values of fat-free mass/lean body mass (%) in children and adolescents with insulin resistance/glucose tolerance/metabolic syndrome and higher values of fat-free mass/lean body mass when these are expressed in kg. The evidence of the impact of lean mass on children's glucose homeostasis or metabolic syndrome is limited, so future studies research should focus on explaining the effect of fat-free mass/lean body mass on different metabolic outcomes. Moreover, it may be interesting to evaluate the quality (muscle density) or functional (muscle strength) outcomes in addition to both absolute (kg) and relative (%) values in future studies. The systematic review was prospectively registered at PROSPERO (registration number CRD42019124734; available at: http://www.crd.york.ac.uk/prospero [accessed: 05 April 2019]).

Is an Exercise Intervention the only way to Reduce Visceral Fat without Reducing Fat-free Mass in Children and Adolescents?

Objectives: To maintain proper development, it is recommended that children/adolescents focus more on increasing physical activity than dietary restriction when treating obesity. In other words, adults are better able to tolerate the reductions in fat-free body mass that often occur when trying to lose fat mass. In contrast, children and adolescents should avoid losses in fat-free mass in order to ensure proper development. Therefore, when trying to reduce visceral fat in children via a negative energy balance (i.e., exercise with or without calorie restriction), it is necessary to set desirable conditions in order to minimize the loss of fat-free mass. To determine whether this is possible, we reviewed literature discussing the relationship between changes in visceral fat obtained by abdominal imaging and changes in total body fat and fat-free mass after exercise training with and without calorie restriction in children and adolescents.Methods: Literature review.Results and Conclusions: Previous work found no reduction in fat-free mass in the exercise interventions in which there was no dietary-induced calorie restriction. This supports the idea that reducing visceral fat by increasing physical activity is the preferred strategy over dietary restriction in children and adolescents. Although factors such as the type (e.g. aerobic and/or resistance) of exercise and the amount (i.e. energy expenditure) of exercise will likely have an effect on the magnitude of change in intra-abdominal visceral fat, the quantity of each that is needed without reducing fat-free mass is currently unknown.

Temporal and mediation relations of weight loss, and changes in insulin resistance and blood pressure in response to 2-year weight-loss diet interventions: the POUNDS Lost trial

PURPOSE

Body weight and insulin resistance (IR) are closely correlated, and their temporal sequences in affecting blood pressure (BP) remain poorly defined. We examined the temporal sequences of weight loss and IR change, and their relations with BP in the Pounds Lost trial, a randomized weight-loss diet intervention study.

METHODS

The present study included overweight/obese adults, who were randomized in a 2 × 2 factorial design to low-calorie diets containing 20 or 40% fat and 15 or 25% protein (diets with 65, 55, 45 and 35% carbohydrate). Weight, IR, systolic and diastolic BP levels were measured at baseline, 6 and 24 months. After excluding the subjects who took antihypertensive drugs, cross-lagged path and mediation analyses were performed among 540 participants.

RESULTS

After adjusting for age, race, sex, and diet groups, the cross-lagged path coefficient from baseline weight to 24-month IR (β₁ = 0.135, P = 0.04) was significantly greater than the path coefficient (β₂ = 0.022, P > 0.05) from baseline IR to 24-month weight (P < 0.05 for the difference in βs), indicating that weight-loss preceded change of IR. The mediation effects of 24-month IR on the 24-month systolic BP and diastolic BP were estimated at 20.94% (P = 0.004) and 17.03% (P = 0.034), respectively.

CONCLUSIONS

Our data indicate that weight loss precedes change of IR, which mediates a significant proportion of the effects of weight loss on changes of BP in response to the diet interventions.

TRIAL REGISTRATION

NCT00072995 First Posted November 17, 2003 Last Update Posted January 30, 2013 this study was not 'retrospectively registered'.