Mammalian lignans such as enterolactone and enterodiol, which are produced in the colon from precursors in foods, have been suggested as playing a role in the cancer-protective effect of vegetarian diets. Despite this, very little is known regarding the amount that is produced from different food products. Therefore, the objective of this study was to determine the production of mammalian lignans from 68 common plant foods by using the technique of in vitro fermentation with human fecal microbiota, which simulates colonic fermentation. Results showed a wide range (21-67,541 microgram(s)/100 g sample) in the amount of lignans produced. On the average as a group, the oilseeds produced the highest amounts (20,461 +/- 12,685), followed by the dried seaweeds (900 +/- 247), whole legumes (562 +/- 211), cereal brans (486 +/- 90), legume hulls (371 +/- 52), whole grain cereals (359 +/- 81), vegetables (144 +/- 23), and fruits (84 +/- 22). The vegetables produced the second highest concentration of lignans (1,546 +/- 280) when the data were expressed on a moisture-free basis. Flaxseed flour and its defatted meal were the highest producers of lignans (mean 60,110 +/- 7,431). Lignan production with the in vitro method related well to the urinary lignan excretion observed in rats and humans. The data should be useful in the estimation of lignan production from a given diet and in the formulation of high-lignan-producing diet for the purpose of reducing the cancer risk.

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Guar and psyllium are fermented by human fecal bacteria in vitro. To see if they were fermented in vivo, eight subjects were studied over 3 separate days, in random order, while eating a polysaccharide-free diet. Twenty grams guar or psyllium, taken at breakfast, had no effect on breath hydrogen levels over 14 h. Mean breath methane and serum acetate concentrations after guar, 37 +/- 1 ppm and 93 +/- 6 mumol/L, respectively, were significantly greater than after control, 20 +/- 2 ppm (P less than 0.05) and 62 +/- 4 mumol/L (P less than 0.01), and psyllium, 20 +/- 2 ppm (P less than 0.05) and 78 +/- 6 mumol/L (P less than 0.05). Serum acetate increased after guar (area under curve 193 +/- 56 mumol.h/L; P less than 0.02) but decreased after psyllium and control. We conclude that guar is fermented in the human colon, producing rises in breath methane and serum acetate but not hydrogen. Although psyllium had no effect on hydrogen, methane, or acetate, this does not prove that it is not fermented.