After a 1 g/kg dose of fructose, blood levels increase minimally to just ∼0.5 mM,22 much less than the 10 mM increase found with an equivalent dose of glucose. Fructose metabolism also differs from glucose metabolism in that uptake is relatively unregulated by insulin.25 Fructokinase action is 10 times faster than glucokinase and hexokinase, and fructose accumulates

in the liver as fructose-1-phosphate.26 Perfusion studies of liver tissue show that this step is rapid enough to precipitate a depletion of adenosine triphosphate (ATP) content to 23%, although ATP recovers to normal within 40 minutes.27 Fructose-1-phosphate is converted into triose phosphates, which become substrates for gluconeogenesis or the downstream C59 wnt mw steps of glycolysis and DNL. In a 6-hour study tracking the fate of an oral bolus of labeled fructose, 35% of fructose was oxidized, 0.4% appeared as FFA in newly formed VLDL-TG, 38% appeared as glycerol

in VLDL-TG, and some remained unaccounted for, likely remaining in the liver in the selleck compound form of glycogen.28 In sum, fructose metabolism is unique from glucose; it enters the liver in a relatively unregulated fashion and is metabolized into products of both glycolysis and gluconeogenesis.29 Paradoxically, although fructose does not increase insulin acutely, over time it increases insulin resistance, fasting glucose, and insulin. Dirlewanger et al.30 found that fructose induces hepatic and extrahepatic insulin resistance in healthy adult humans in infusion/clamp studies, although the mechanism of how insulin resistance is induced is not known. High fructose consumption clearly increases visceral fat in healthy adults and in animal models (see Supporting Material). In SPTBN5 a 10-week study, subjects consuming fructose beverages gained significantly more visceral adiposity compared

to those consuming eucaloric glucose beverages.31 A cross-sectional study of adolescents also found a relationship between high fructose consumption and visceral adiposity.32 It may be that induction of visceral fat results in increased insulin resistance because visceral fat is thought to be inherently “diabetogenic.”33 However, it is also possible that the deposition of lipids in the liver causes insulin resistance and leads to increased visceral adiposity.33 Stanhope and Havel34 postulate that decreased insulin stimulation by fructose leads to decreased lipoprotein lipase activity in saturated adipose tissue and increased lipoprotein lipase activity in visceral adipose tissue, thus leading to increased lipid uptake into the hypertrophied adipocytes. In 1970, Mann et al.35 demonstrated that sucrose reduction in the diet resulted in improved TG levels in healthy men. This finding continues to be supported by numerous studies demonstrating a hypertriglyceridemic effect of fructose in humans.