Why are we shaped differently, and why does it matter?

Abstract

Body fat distribution is an important predictor of metabolic abnormalities in obese humans. Dysregulation of free fatty acid (FFA) release, especially from upper body subcutaneous adipose tissue, appears to contribute substantially to these metabolic disturbances. Why different individuals preferentially store fat in upper vs. lower body subcutaneous fat or subcutaneous vs. visceral fat is not completely understood. Current evidence suggests that defects in regional lipolysis are not the cause of net fat retention in larger fat depots. Regional variations in the storage of fatty acids, both meal derived and direct reuptake, and storage of circulating FFAs that may help to explain why some depots expand at the expense of others have been reported. We review the quantitative data on regional lipolysis, meal, and FFA storage in adults to provide an overview of fat balance differences in adults with different fat distribution patterns.

Fig. 1.

Fatty acid kinetics (in g) over 24 h in a normal-weight (body mass index ∼22.5 kg/m²) man with 15% body fat and a normal-weight woman with 30% body fat are depicted. To make the calculations, we assumed that 14, 8, and 2 h of the day were spent in the postprandial state, in the postabsorptive state, and doing physical activity at a level that would affect lipolysis and fat oxidation, respectively. Regional fatty acid metabolism is represented from legs to chest as lower body subcutaneous adipose tissue, visceral adipose tissue, and upper body subcutaneous adipose tissue. Green arrows represent the regional meal fat storage via lipoprotein lipase-mediated pathways and oxidation assuming a 75 g/day ingestion of meal fat. Blue arrows represent the direct storage of free fatty acids into regional depots from the circulating free fatty acid (FFA) pool. Red arrows indicate the regional flow of FFAs that enter the circulation via lipolysis. Size of arrow is proportional to the contributory flow of FFAs to each pool. Reprinted with permission from the Mayo Foundation for Medical Education and Research.