Specific types of colonic fermentation may raise low-density-lipoprotein-cholesterol concentrations

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Abstract
To assess the effects of increased colonic fermentation on serum lipids, eight healthy volunteers were placed on two identical 2-wk metabolic diets, one of which was supplemented with lactulose (18–25 g/d). Lactulose raised day-long concentrations of breath hydrogen and serum glutamine as indicators of increased colonic fermentation by 78 ± 13% (P < 0.001) and 24.7 ± 9.5% (P < 0.05), respectively). Unexpectedly, however, fasting serum total and low-density-lipoprotein cholesterol and apolipoprotein B concentrations were higher at 2 wk by 8.9 ± 1.5% (P < 0.001), 10.9 ± 2.2% (P < 0.005), and 18.9 ± 5.9% (P < 0.02), respectively, compared with the control diet. With lactulose, mean free fatty acid concentrations were reduced over the day by 19.5 ± 5.9% (P < 0.02), with no change in mean day-long blood glucose, serum insulin, or C-peptide concentrations. We conclude that certain rapidly fermented substrates may raise rather than lower serum lipids, possibly through increasing the amount of acetate absorbed from the colon.