Fat distribution and metabolic health: The effects of macronutrient manipulation on fat distribution, weight loss, and glucose metabolism

Fat distribution pattern may contribute to risk of development of metabolic diseases such and type 2 diabetes and cardiovascular disease. However, the precise nature of the relationships between adipose tissue depots and metabolic health remains controversial. Additionally, further research is needed to identify optimal dietary approaches to reduce disease risk and visceral adiposity among overweight and obese individuals, who may already be on a trajectory for development of metabolic disease. Therefore, the goal of this project was to examine relationships of adipose tissue depots with insulin sensitivity, and then to determine if diets differing in CHO and fat content can modulate fat distribution, thereby improving indices of metabolic health. Thus, the first aim of this project was to identify independent associations of adipose tissue depots with insulin sensitivity among postmenopausal women. Additional aims of this project were to determine whether consumption of a low vs high glycemic load (GL) diet would reduce total and visceral adipose tissue under both eucaloric and hypocaloric conditions, and further to determine if under eucaloric conditions, the low GL/higher fat diet influenced sex hormone-binding globulin (SHBG) and parameters of glucose metabolism.

To address the first aim, 97 healthy, early postmenopausal women underwent testing of: body composition by dual-energy X-ray absorptiometry (DXA), fat distribution by computed tomography (CT), and insulin sensitivity by frequently sampled intravenous glucose tolerance test. For the next two aims, 69 healthy overweight participants were assigned to either a low GL diet (43%CHO, 18%PRO, 39%FAT) or high GL diet (55%CHO, 18%PRO, 27%FAT). Body composition was assessed by DXA and fat distribution by CT at baseline and after 8 weeks of a eucaloric diet intervention and 8 weeks of a hypocaloric diet intervention. Additionally, for the third aim, serum fasting SHBG, fasting glucose, fasting insulin, and glucose area under the curve following a standard liquid mixed macronutrient meal were assessed at baseline and following the eucaloric phase.

Results from these studies indicate that maintaining greater SAT and lesser IAAT or thigh IMAT promotes or reflects greater insulin sensitivity. Also, consumption of a low vs high GL diet resulted in preferential loss of IAAT during weight maintenance and greater total fat loss during caloric restriction. However, during eucaloric conditions this diet also resulted in reduced SHBG, which was associated with change in fasting and post-challenge glucose.