José L. Peñalvo

Lignan content of selected foods from Japan.

Lignans constitute a group of phytochemicals widely distributed in the human diet. Once ingested, most dietary lignans are metabolized by the gut microflora to enterolactone and enterodiol, also known as enterolignans. Together with isoflavones and coumestrol, enterolignans have been traditionally classified as phytoestrogens, plant-derived compounds that exhibit estrogen-like activity. In addition to a higher intake of vegetables, many studies have suggested that the presence of phytoestrogens in the Japanese diet is one of the factors that might explain the reduced incidence of certain chronic diseases in Japanese populations compared with Western countries. Being a vegetable-based diet, exposure to dietary lignans should be high, but to assess this exposure, a lignan food database is required. Stable isotope-dilution gas chromatography coupled with mass spectrometry was used to quantify six plant lignans in 86 food items commonly consumed in Japan. These data will complement the previous databases and most importantly expand the knowledge of occurrence of lignans in food to Eastern diets.

Dietary intake and urinary excretion of lignans in Finnish men

Intake of lignans has been assessed in different study populations, but so far none of the studies has compared the daily intake of lignans and the urinary excretion of plant and enterolignans. We assessed the intake of lariciresinol, pinoresinol, secoisolariciresinol and matairesinol in 100 Finnish men consuming their habitual omnivorous diet, and measured the 24 h urinary excretion of plant and enterolignans to compare the intake and metabolism. Dietary determinants of lignan intake and their urinary excretion were also determined. The mean intake of lignans was 1224 (sd 539) mug/d, of which lariciresinol and pinoresinol covered 78 %. Almost half (47 %) of the intake of lignans was explained by the intake of rye products, berries, coffee, tea and roots. The urinary excretion of plant lignans corresponded to 17 % and enterolignans to 92 % of the intake of lignans. The urinary excretion of plant lignans was explained 14 % by the intake of rye products and intake of coffee, and consequently 3-7 % by the intake of water-insoluble fibre. The urinary excretion of enterolactone was explained 11 % by the intake of vegetables and rye products, 14 % by the intake of water-soluble fibre and only 4 % by the intake of lariciresinol. Although the assessed intake of lignans corresponded well with the urinary excretion of lignans, the enterolactone production in the human body depended more on the dietary sources of lignans than the absolute intake of lignans.

Kinetics of the appearance of cereal alkylresorcinols in pig plasma.

Alkylresorcinols (AR) are phenolic lipids found in high amounts in wholegrain wheat and rye. They may be important as bioactive components and/or biomarkers of wholegrain wheat and rye intake. AR absorption was studied with pigs during a habitual diet and after a single meal of AR-rich diet. In study 1, four pigs were fed wholegrain rye (RD) and white wheat bread (WD) for 1 week in a cross-over design. Arterial and venous AR concentrations were determined over 540 min after feeding on days 5 and 7. In study 2, four pigs were fed a synthetic, starch-based diet for 5 d, and arterial and venous AR concentrations were determined over 960 min after feeding a single meal of RD. In study 1, plasma AR concentrations after consuming RD peaked at 120 min, remained elevated between 120 and 420 min, and were re-elevated on refeeding at 480 min. In study 2, AR appeared in the plasma after 60 min, peaked at 180-240 min, and remained elevated after 960 min. The apparent elimination half-life was 3.93 h, and the maximum plasma concentration was 666 (sem 35) nmol/l. Arterial and venous plasma AR concentrations were similar, suggesting that AR are absorbed via the lymphatic system. AR concentrations in pig plasma increase rapidly after a meal containing AR, and persist in plasma for at least 5 d, indicating that AR may be a useful biomarker of wholegrain wheat and rye intake.

Quantitative aspects of the metabolism of lignans in pigs fed fibre-enriched rye and wheat bread.

A diet rich in lignans has been suggested to be protective against a range of chronic diseases. The distribution and metabolic fate of lignans is, however, very poorly understood. We fed high-fibre wheat breads low in lignans (n 8) or high-fibre rye breads (n 9) rich in plant lignans to pigs for 58-67 d, and analysed the content of plant lignans and their metabolites in the diet, blood, bile, faeces, urine and selected tissues. Apparent faecal digestibility of dietary precursors was higher than of total (plant- and entero-) lignans due to conversion to enterolactone and enterodiol. The digestibility of lariciresinol and matairesinol was lower than that of the sum of plant lignans. This suggests that interconversion of plant lignans during digestion and enterohepatic circulation occur without complete conversion to enterolignans. The majority of lignans present in plasma and urine was in the form of enterolignans, but up to 23 % in the plasma, and 11 % in the urine of the rye-fed pigs were in the form of plant lignans. There was a very high concentration of lignans in bile from the rye-fed pigs with as much as 77 % in the form of plant lignans. Lignans were detected in the tissue of colon, liver, breast and brain at a much higher level with rye than with wheat, but only in the form of enterolactone. The importance and implications of systemic exposure to plant lignans remain to be elucidated.

Flaxseed Ingestion Alters Ratio of Enterolactone Enantiomers in Human Serum

Enterolactone (EL) is an enterolignan found in human subjects. In this pilot study, the enantiomeric ratios of serum EL were determined in serum from healthy adults during consumption of habitual diet, and after an 8-day supplementation with flaxseed (25 g/day). (−)EL dominated in all serum samples collected during habitual diet consumption. However, the ratio of (−)EL and (+)EL enantiomers differed markedly between individuals. Flaxseed ingestion increased significantly the proportion of (+)EL in all subjects. Moreover, a small but significant increase in serum (−)EL concentration was measured. After flaxseed ingestion, (−)EL concentrations correlated with those of (+)EL suggesting that the stereochemistry of the parent plant lignan in flaxseed is not a major determinant of EL formation in human subjects. Comparison of EL concentrations obtained with the validated chromatographic methods (HPLC-MS/MS, HPLC-CEAD, and GC-MS) and the time-resolved fluoroimmunoassay (TR-FIA) revealed that the immunoassay method underestimates human serum EL concentrations after the flaxseed ingestion.