ReviewExercise and ectopic fat in type 2 diabetes: A systematic review and meta-analysis
Introduction
Overweight and obesity contributes to the increased worldwide prevalence of cardiovascular and metabolic morbidity and mortality [1]. Evidence also suggests that the location of excess adiposity, particularly that stored around the organs as visceral adipose tissue (VAT), is of greater importance in determining adverse health outcomes than the larger subcutaneous adipose tissue reserves [2]. More recently, excess adiposity within lean tissues has been associated with the underlying pathophysiological characteristics of type 2 diabetes. For instance, increased fat within the liver is associated with insulin resistance [3], impaired glycaemic control [4] and increased cardiovascular disease risk [2]. Similarly, small amounts of fat within muscle cells, the pancreas and myocardium and have been linked with peripheral insulin resistance [5], impaired insulin secretion [6] and hypertension/cardiomyopathy [7], respectively. Given the association between these “ectopic fats” [8] and adverse metabolic and cardiovascular outcomes, it is important to determine the efficacy of interventions, which aim to reduce ectopic fat in type 2 diabetes.
Although there are surgical [9] and pharmaceutical [10] interventions which assist in obesity and ectopic fat reduction, access, cost, and side-effects limit their usefulness for type 2 management at a population level, particularly in the Middle East and North Africa regions where two out of five adults with diabetes are believed to be undiagnosed [11].
Lifestyle modification involving exercise is considered to be the first line of therapy [1] for obesity-related type 2 diabetes, and produces a well-established multiplicity of benefits such as improved insulin sensitivity, and glycaemic control [12]. Although the consensus of evidence demonstrates that regular exercise may benefit body weight reduction, the effect is typically small when compared with other weight loss therapies [13]. Recently, studies have suggested regular exercise may decrease VAT and liver fat and improve cardio-metabolic outcomes [14], [15].
As ectopic fat increases the risk for developing type 2 diabetes, and populations with type 2 diabetes may be at a higher risk of excess ectopic fat accumulation independent of BMI [16], we aimed to assess the efficacy of exercise as an intervention to reduce ectopic fat in type 2 diabetes via systematic review and meta-analyses of pooled data from randomised controlled adult human studies.
Section snippets
Search
Electronic database searches were performed by two researchers (AS and KW) in Medline (Ovid), Cinahl (EBSCO Host), AMED (Ovid), Web of Science (ISI Web of Knowledge), SportDisucs (EBSCO Host), and Embase (Ovid) from earliest record to February 2016. The search was performed using keywords covering the area of exercise and ectopic fat. Specifically, keywords searched were: (aerobic exercise, endurance exercise, aerobic training, endurance training, cardio training, exercise, physical endurance,
Identification and selection of studies
The original search identified 10,750 studies. After removal of duplicates and elimination of papers based on the eligibility criteria, 24 studies remained (Fig. 1). Of the 24 studies included, six [17], [22], [23], [24], [25], [26] assessed the effect of exercise on liver fat, of which two [22], [26] did not report complete pre- and post-intervention measures and thus four [17], [23], [24], [25] were included in the meta-analysis. Eighteen studies [25], [27], [28], [29], [30], [31], [32], [33]
Discussion
This systematic review and meta-analysis assessed the efficacy of exercise interventions in reducing ectopic fat in adults with type 2 diabetes. All 13 studies included in the meta-analysis assessing the effect of exercise on VAT, showed an effect size favouring exercise, however no individual report was statistically significant. Similarly, the four studies included in the meta-analysis assessing the effect of exercise on liver fat, showed an effect size favouring exercise, however no
Funding
Nil.
Disclosure of interest
The authors declare that they have no competing interest.
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