Changes in body composition, energy metabolism and muscle function following a very low calorie diet and bariatric surgery

Abstract

Background and aim: Bariatric surgery is an effective intervention for the management of obesity. Bariatric patients are often required to go on a Very Low Calorie Diet (VLCD) before surgery. There is limited research regarding the effect of VLCD and bariatric surgery on changes in body composition, energy metabolism, and functional changes. The aims of this thesis were to investigate, in a cohort of women undergoing bariatric surgery, the body composition, energy metabolism and muscle function changes that occur (1) during a period of VLCD prior to surgery, and (2) over the six month period following surgery. Methods: This thesis analysed the data of participants who underwent the Optifast VLCD (600- 800kcal/d) and bariatric surgery. Data were collected prior to commencement of the VLCD, a day before surgery, and six months after surgery. Body composition was measured using anthropometry, dual-energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA), and whole body counting. Muscle function was measured through the handgrip test. Energy metabolism was measured using indirect calorimetry. Outcome measures included body weight, fat mass (FM), fat-free mass (FFM), waist circumference (WC), waist-to-hip ratio (WHR), trunk fat:limb fat ratio (TLFR), mid-arm muscle area (MAMA), total muscle mass by anthropometry, appendicular skeletal muscle mass (ASMM), total body potassium (TBK), bone mineral density (BMD), phase angle (PhA), impedance ratio (IR), handgrip strength and resting energy expenditure (REE). Results: Twenty-six participants were included in pre/post-VLCD analysis. Participants underwent the Optifast VLCD for 32±8 days and showed a significant reduction in body weight (p<0.0001), DXA FM (p<0.0001), DXA FFM (p<0.0001), WC (p=0.0002), WHR (p=0.028), ASMM (p=0.0004), TBK (p<0.0001) and REE (p<0.0001). FM as measured by DXA comprised 46% of the 7.4 kg loss in body weight. Metabolic adaptation was also seen after the period of VLCD. There was no significant reduction in MAMA, estimated total muscle mass by MAMA, BMD, TLFR, PhA, IR, and handgrip strength after VLCD. Twenty-six participants were included in pre/post-surgery analysis. Participants who underwent bariatric surgery showed a significant reduction in body weight, FM, FFM, WC, WHR, TLFR, MAMA, estimated total muscle mass by MAMA, ASMM, TBK, handgrip strength, BMD, PhA, IR and REE (all significant at p<0.0001). FM as measured by DXA comprised 80% of the 25.5 kg loss in body weight. Metabolic adaptation was not seen at six months after bariatric surgery. Conclusions: Reductions in body weight, FM and central obesity highlight the effectiveness of VLCD and bariatric surgery in managing obesity and reducing the risk of metabolic disease. As a percentage of weight lost, FFM loss was much lower after surgery than after VLCD. However, reductions in FFM, muscle mass, handgrip strength and BMD after bariatric surgery indicate negative consequences of these treatment options. Metabolic adaptation indicating a propensity for weight regain was evident after VLCD but not at 6 months after surgery. Longer term follow-up after surgery is needed to confirm whether this lack of adaptation persists.