Dietary sugars stimulate fatty acid synthesis in adults

Abstract

The goal of this study was to determine the magnitude by which acute consumption of fructose in a morning bolus would stimulate lipogenesis (measured by infusion of 13C1-acetate and analysis by GC-MS) immediately and after a subsequent meal. Six healthy subjects [4 men and 2 women; aged (mean +/- SD) 28 +/- 8 y; BMI, 24.3 +/- 2.8 kg/m(2); and serum triacylglycerols (TG), 1.03 +/- 0.32 mmol/L] consumed carbohydrate boluses of sugars (85 g each) in a random and blinded order, followed by a standardized lunch 4 h later. Subjects completed a control test of glucose (100:0) and a mixture of 50:50 glucose:fructose and one of 25:75 (wt:wt). Following the morning boluses, serum glucose and insulin after 100:0 were greater than both other treatments (P < 0.05) and this pattern occurred again after lunch. In the morning, fractional lipogenesis was stimulated when subjects ingested fructose and peaked at 15.9 +/- 5.4% after the 50:50 treatment and at 16.9 +/- 5.2% after the 25:75 treatment, values that were greater than after the 100:0 treatment (7.8 +/- 5.7%; P < 0.02). When fructose was consumed, absolute lipogenesis was 2-fold greater than when it was absent (100:0). Postlunch, serum TG were 11-29% greater than 100:0 and TG-rich lipoprotein-TG concentrations were 76-200% greater after 50:50 and 25:75 were consumed (P < 0.05). The data demonstrate that an early stimulation of lipogenesis after fructose, consumed in a mixture of sugars, augments subsequent postprandial lipemia. The postlunch blood TG elevation was only partially due to carry-over from the morning. Acute intake of fructose stimulates lipogenesis and may create a metabolic milieu that enhances subsequent esterification of fatty acids flowing to the liver to elevate TG synthesis postprandially.

FIGURE 1

Study protocol. An i.v. line was placed on d 1 and ¹³C₁-acetate infused for 25 h. The CHO solutions were fed between 0745 and 0800 and a standardized lunch was served at 1205 (4.33 h).

FIGURE 2

Concentrations of serum glucose (A), insulin (B), NEFA (C), and TG (D) after consumption of CHO solutions and a lunch. Values are means ± SEM, n = 6. Time 0 denotes when the CHO bolus was fed. The solid food lunch was fed at 4.33 h (denoted by arrow).

FIGURE 3

tTRL-TG concentrations (A) and fractional (B) and absolute lipogenesis (C). Values are means ± SEM, n = 6. Time 0 denotes 0745 when the CHO bolus was fed. The solid food lunch was fed at 4.33 h. Abbreviations: abs, absolute; fxn, fractional.

FIGURE 4

Sf > 400 and Sf 60–400 lipoprotein-TG concentrations (A and D), and fractional (B and E) and absolute lipogenesis (C and F). Values are means ± SEM, n = 6. Time 0 denotes 0745 when the CHO bolus was fed. The solid food lunch was fed at 4.33 h.