Insulin-resistant states are characterized by hypertriglyceridemia, predominantly because of overproduction of hepatic very low density lipoprotein particles. The additional contribution of intestinal lipoprotein overproduction to the dyslipidemia of insulin-resistant states has not been previously appreciated. Here, we have investigated intestinal lipoprotein production in a fructose-fed hamster model of insulin resistance previously documented to have whole body and hepatic insulin resistance, and hepatic very low density lipoprotein overproduction. Chronic fructose feeding for 3 weeks induced significant oversecretion of apolipoprotein B48 (apoB48)-containing lipoproteins in the fasting state and during steady state fat feeding, based on (a) in vivo Triton WR1339 studies of apoB48 production as well as (b) ex vivo pulse-chase labeling of intestinal enterocytes from fasted and fed hamsters. ApoB48 particle overproduction was accompanied by increased intracellular apoB48 stability, enhanced lipid synthesis, higher abundance of microsomal triglyceride transfer protein mass, and a significant shift toward the secretion of larger chylomicron-like particles. ApoB48 particle overproduction was not observed with short-term fructose feeding or in vitro incubation of enterocytes with fructose. Secretion of intestinal apoB48 and triglyceride was closely linked to intestinal enterocyte de novo lipogenesis, which was up-regulated in fructose-fed hamsters. Inhibition of fatty acid synthesis by cerulenin, a fatty acid synthase inhibitor, resulted in a dose-dependent decrease in intestinal apoB48 secretion. Overall, these findings further suggest that intestinal overproduction of apoB48 lipoproteins should also be considered as a major contributor to the fasting and postprandial dyslipidemia observed in response to chronic fructose feeding and development of an insulin-resistant state.The metabolic syndrome, which is characterized by fasting hypertriglyceridemia, insulin resistance, glucose intolerance, hypertension, and obesity (1), appears also to include impaired postprandial lipoprotein metabolism (2, 3). Postprandial triglyceride-rich lipoproteins and especially chylomicron remnants have been implicated as risk factors for atherosclerosis and progression of coronary artery disease, based on both experimental work (4, 5) and cross-sectional studies (6 -8). Emerging evidence suggest that intestinal lipoproteins may be particularly atherogenic in diabetes (9). We (10, 11) and others (12-15) have shown previously that there is an elevation of postprandial triglyceride (TG) 1 -rich lipoproteins in subjects with insulin resistance and type 2 diabetes and that fasting hypertriglyceridemia predicts this abnormal postprandial response to a fat load. A strong correlation also exists between plasma insulin and the postprandial TG response to a fat meal, and the postprandial levels of large VLDLs and chylomicron remnants (3, 16). In the fasting state, plasma insulin, a marker of insulin resistance, is also related to fasting plas...