Relationship between body fat mass and free fatty acid kinetics in men and women

Abstract

An increased release of free fatty acids (FFAs) into plasma likely contributes to the metabolic complications associated with obesity. However, the relationship between body fat and FFA metabolism is unclear because of conflicting results from different studies. The goal of our study was to determine the inter-relationships between body fat, sex, and plasma FFA kinetics. We determined FFA rate of appearance (Ra) in plasma, by using stable isotopically labeled tracer techniques, during basal conditions in 106 lean, overweight, and obese, nondiabetic subjects (43 men and 63 women who had 7.0-56.0% body fat). Correlation analyses demonstrated: (i) no differences between men and women in the relationship between fat mass (FM) and total FFA Ra (micromol/min); (ii) total FFA Ra increased linearly with increasing FM (r=0.652, P<0.001); (iii) FFA Ra per kg FM decreased in a curvilinear fashion with increasing FM (r=-0.806; P<0.001); (iv) FFA Ra in relationship to fat-free mass (FFM) was greater in obese than lean subjects and greater in women than in men; and (v) abdominal fat itself was not an important determinant of total FFA Ra. We conclude that total body fat, not regional fat distribution or sex, is an important modulator of the rate of FFA release into plasma. Although increased adiposity is associated with a decrease in fatty acid release in relationship to FM, this downregulation is unable to completely compensate for the increase in FM, so total FFA Ra and FFA Ra with respect to FFM are greater in women than in men and in obese than in lean subjects.

Figure 1

Relationship between FM and total FFA Ra (top panel) and FFM and total FFA Ra (bottom panel) in men (n = 43; filled squares) and women (n = 63; open circles). The strength of the relationship was evaluated by using the Pearson product-moment correlation coefficient (R-value) and corresponding P-values. FFA: free fatty acid; FFM: fat-free mass; FM: fat mass; Ra: rate of appearance in plasma.

Figure 2

Relationship between FM and FFA Ra per kg FM (top panel) and FM and FFA Ra per kg FFM (bottom panel) in men (n = 43; filled squares) and women (n = 63; open circles). The strength of the relationship was evaluated by using the Pearson product-moment correlation coefficient (R-value) and corresponding P-values. The intercepts of the regression lines describing the relationship between FM and FFA Ra per kg FFM for men and women were different (P <0.002). FFA: free fatty acid; FFM: fat-free mass; FM: fat mass; Ra: rate of appearance in plasma.