Effects of Exercise Training on Liver Fat and Circulating Immune Markers in People who are Obese or Overweight with Normal or Dysglycaemia

Abstract

Aims: This thesis aimed to examine the efficacy of exercise to reduce liver fat firstly via meta-analysis and then through investigation of a novel exercise modality; low volume high intensity interval training with combined progressive resistance training. This thesis also investigates circulating immune markers in adults with obesity and either normal glucose (NG) or prediabetes, and the effects of a novel exercise intervention.

Results: The meta-analysis found that exercise was able to reduce liver fat by -2.4%, -3.13 to -1.66 (mean, 95% CI). In this randomised control trial study, people with prediabetes had increased liver fat compared to NG (absolute % liver fat in prediabetes: 11.4 ± 1.7, in NG: 5.2 ± 1.1, p= 0.002) despite having similar BMI at baseline. In a RCT involving a subgroup only of those in the PACE-G study, the exercise intervention (NG n=37, Prediabetes n=31), vs sham (NG n=39, Prediabetes n=29), showed a small effect on liver fat, which was not statistically significant when compared with control (NG exercise vs control: -0.7±0.7%, prediabetes exercise vs control: -1.2±0.9%). With respect to circulating cytokines IL-8 was significantly higher in NG than prediabetes and IL-15 and IL-22 were higher in prediabetes than NG. Interestingly, adults with prediabetes who undertook the exercise intervention did not realise the same reduction in pro-inflammatory cytokines as adults with NG. Finally, adults with prediabetes had reduced circulating angiogenic CD8+ T cells. Adults who undertook the exercise intervention improved circulating angiogenic T cells.

Conclusions: The work in this thesis shows that while only some types of exercise may improve metabolism and liver fat and novel CV risk markers may still be improved by certain exercise regimens even when metabolism is not overtly improved.