Title: Methane producing status, lipids and short chain fatty acids in humans
Description: It has been theorized that colonic production and absorption of short chain fatty acids (SCFA) is different in methane producers (MP) compared to nonproducers (MNP). Thus, it was hypothesised that MP have higher serum cholesterol concentrations than MNP, possibly, due to increased colonic acetate availability being a substrate for cholesterol synthesis. To test this, fasting serum lipids and SCFA were compared in 66 MP and 63 MNP. The MP were significantly older than MNP (49.5±2.0 vs 39.6±2.2y, P<0.005) and breath methane concentrations were weakly correlated with age in MP. MP had higher serum cholesterol than MNP (5.5±0.1 vs 5.0±0.1mmol/L, P=0.02), but the difference was not significant after age adjustment. No significant differences were observed in serum SCFA between the groups. 3-day diet records revealed no difference in macronutrient intakes between MP and MNP. Dietary fiber intake in MP, 23.2±1.4 g, was significantly higher than in MNP 18.1±1.3g (P<0.01), but the difference was not significant after age adjustment. Dietary fiber intake was positively correlated with breath methane in MP. In the second study in vitro production of SCFA in MP and MNP was determined. No differences were observed in the fermentation of different substrates between the groups, but there were highly significant differences between substrates in the whole group. To determine if MP have higher post-prandial serum acetate concentrations over  12-hours than MNP, 11 MP and 8 MNP with impaired glucose tolerance (IGT) were studied. MP had significantly greater fasting serum cholesterol and LDL cholesterol than MNP. The mean increment in serum acetate over 6-12 hours in MP was significantly higher than MNP. In summary, the study in healthy humans showed that MP had significantly higher fasting serum cholesterol than MNP, it is unclear if this is age-related. Methane producing status (MPS) is linked to age and fiber intake. In vitro production of SCFA is not affected by MPS but the results point to increased absorption of SCFA in MP. In IGT subjects, a positive MPS increases post-prandial serum acetate which may contribute to the increased serum total cholesterol concentration.