The effect of haem in red and processed meat on the endogenous formation of N-nitroso compounds in the upper gastrointestinal tract.

Red and processed meat (PM) consumption increases the risk of large bowel cancer and it has been demonstrated that haem in red meat (RM) stimulates the endogenous production of N-nitroso compounds (NOCs) within the human intestine. To investigate whether N-nitrosation occurs in the upper gastrointestinal tract, 27 ileostomists were fed diets containing no meat, or 240 g RM or 240 g PM in a randomly assigned crossover intervention design carried out in a volunteer suite. Endogenous NOC were assessed as apparent total N-nitroso compounds (ATNC) in the ileostomy output. ATNC concentration in the diets was 22 microg ATNC/kg (RM) and 37 microg ATNC/kg (PM), and 9 microg ATNC/kg in the no meat diet. Levels significantly increased to 1175 microg ATNC/kg SEM = 226 microg ATNC/kg) following the RM (P=0.001) and 1832 microg ATNC/kg (SEM=294 microg ATNC/kg) following PM (P<0.001) compared to the no meat diet (283 microg ATNC/kg, SEM=74 microg ATNC/kg). ATNC concentrations in the ileal output were equivalent to those measured in faeces in similarly designed feeding studies. Supplementation with either 1 g ascorbic acid or 400 IU alpha-tocopherol had no effect on the concentration of ATNC detected in the ileal output. In in vitro experiments, N-nitrosomorpholine (NMor) was formed in the presence of nitrosated haemoglobin, at pH 6.8 but not in the absence of nitrosated haemoglobin. These findings demonstrate that haem may facilitate the formation of NOC in the absence of colonic flora in the upper human gastrointestinal tract.

Intakes and sources of soya foods and isoflavones in a UK population cohort study (EPIC-Norfolk).

BACKGROUND: It has been suggested that the consumption of a diet rich in phytoestrogens might protect against a variety of diseases common in Western societies. However, there are little available data on the food sources or distribution of intake in the UK diet. OBJECTIVE: To estimate the average intake and range of soya foods and isoflavones in a population-based cohort and to provide data on isoflavone consumption by food group. SUBJECTS: Men and women (11,843) from the Norfolk arm of the European Prospective Investigation into Cancer and Nutrition (EPIC). METHODS: Dietary daidzein and genistein intakes were obtained from 7-day food diaries, completed by participants between 1993 and 1998 and calculated from an in-house food composition database. Energy and anthropometric measurements were also carried out. RESULTS: Average daily isoflavone intakes for both men and women were less than 1 mg (interquartile range (IQR) men: 0.39-0.82 mg; women: 0.30-0.64 mg). However, in soya-consumers, average daily intakes were higher: 8.6 mg in women (IQR: 2.28-10.72 mg) and 7.5 mg in men (IQR: 2.22-9.17 mg). In both men and women, bread and bread rolls made the highest contribution to isoflavone intake - 62.5 and 53.0%, respectively. In soya-consuming men and women, vegetable dishes and milks were the main contributors - 25.0 and 38.5% in men and 38.5% and 26.0% in women, respectively. CONCLUSIONS: Isoflavone intake is low in the UK but may be an underestimate due to soya added to commercial products. Future analyses of the isoflavone and lignan content of basic ingredient foods and commercial items commonly consumed in the UK diet will enable more accurate estimates of phytoestrogen intake to be made. The ability to estimate isoflavone intake in Western populations more accurately will enable investigations to be conducted into the suggested beneficial effects of phytoestrogens on health.

Extraction and quantification of lignan phytoestrogens in food and human samples.

Dietary phytoestrogens have a number of biological effects, including endocrine disruption, antioxidant potential, and protein tyrosine kinase inhibition. Secoisolariciresinol, matairesinol, and shonanin are lignan phytoestrogens found in foodstuffs, especially flaxseed. Normally they are glycosidically linked to carbohydrates and in the large intestine are deconjugated from the carbohydrate portion by bacteria. The aglycone lignans can be further modified to form the mammalian phytoestrogens enterodiol, enterolactone, and enterofuran, which are absorbed into the body and excreted in urine. To assess the health implications of phytoestrogens in general populations, knowledge of the quantity in the foods eaten is necessary. This article describes a simple preparative procedure for the assay of secoisolariciresinol, matairesinol, and shonanin in foodstuffs after hydrolytic removal of any conjugated carbohydrate. The difficulties in the practical application of the assay procedure are illustrated and discussed. Analytical results indicating the concentration of secoisolariciresinol, matairesinol, and shonanin in a number of foodstuffs are presented. Also, the mass spectral data of a putative mammalian phytoestrogen, called enterofuran, identified in urine are presented.

Phyto-oestrogens: where are we now?

Phyto-oestrogens have emerged from their esoteric role in animal husbandry following the hypothesis that the human Western diet is relatively deficient in these substances compared with societies where large amounts of plant foods and legumes are eaten. Evidence is beginning to accrue that they may begin to offer protection against a wide range of human conditions, including breast, bowel, prostate and other cancers, cardiovascular disease, brain function, alcohol abuse, osteoporosis and menopausal symptoms. Of the two main classes of these weak oestrogens, the isoflavones are under intensive investigation due to their high levels in soyabean. Like the 'anti-oestrogen' Tamoxifen, these seem to have oestrogenic effects in human subjects in the cardiovascular system and bone. Although previously only available from food, isoflavones are now being marketed in health-food supplements or drinks, and tablets may soon be available over the counter as 'natural' hormone-replacement therapy. In cancer, anti-oestrogenic effects are thought to be important, although genistein especially has been shown to induce wide-ranging anti-cancer effects in cell lines independent of any hormone-related influence. There are few indications of harmful effects at present, although possible proliferative effects have been reported. In infants, the effects of high levels in soya milk formulas are uncertain. The second group, lignans, have been less investigated despite their known antioestrogenic effects and more widespread occurrence in foods. Investigation of the possible benefits of phyto-oestrogens is hampered by lack of analytical standards and, hence, inadequate methods for the measurement of low levels in most foods. This problem may prove to be a major dilemma for regulatory authorities, clinicians and others wishing to advise the general public on whether these compounds really do have the health benefits attributed to them.

Apolipoprotein E genotype modulates the effect of black tea drinking on blood lipids and blood coagulation factors: a pilot study.

Apolipoprotein E (ApoE) genotype was determined in sixty-five subjects who had taken part in a 4-week randomized crossover trial to compare the effect of six mugs of black tea per day v. placebo on blood lipids and blood coagulation factors. Four ApoE genotype variants (seven E2/E3, forty-five E3/E3, twelve E3/E4 and one E4/E4) were found. ApoE allele frequency was within the range typical for Caucasian populations (ApoE-E2 5.4%; ApoE-E3 83.8%; ApoE-E4 10.8%). Individuals bearing at least one E4 allele had substantially higher levels of serum total cholesterol, LDL cholesterol and triacylglycerols. Mean plasminogen activator inhibitor (PAI-1) activity was higher in ApoE-E4 allele-bearing individuals (E3/E4 + E4/E4, 11.89 (SE 1.27) U/ml; E3/E3, 9.19 (SE 0.80) U/ml; E2/E3, 7.21 (SE 1.04) U/ml, P values of E4-group v. E3 and E2 being respectively 0.093 and 0.030). These unexpected findings imply that elevated PAI-1 activity may be a hitherto unrecognized additional factor involved in the increased cardiovascular disease risk associated with apoE-E4 allele. The interactions between tea drinking and genotype were also examined. In the E3/E3 homozygotes, HDL-cholesterol was significantly reduced in the tea period (mean placebo 1.54 mmol/l v. mean tea 1.50 mmol/l, P = 0.027). In the E2/E3 group, triacylglycerol concentration was significantly reduced (mean placebo 1.18 mmol/l v. mean tea 1.09 mmol/l, P = 0.039). Tea also caused a significant decrease of PAI-1 activity in the subjects with E2/E3 genotype (mean placebo 7.21 U/ml v. mean tea 5.88 U/ml, P = 0.007). In the other two genotype groups, there was no significant effect of tea. The results indicate that tea drinking has a beneficial effect on some cardiovascular disease risk-associated factors, especially in E2 allele-bearing individuals. Dietary intervention may be particularly effective in population groups with certain genetic characteristics.

Effect of black tea drinking on blood lipids, blood pressure and aspects of bowel habit.

Thirty-one men (47 (SD 14) years) and thirty-four women (35 (SD 13) years) took part in a 4-week randomized cross-over trial to compare the effect of six mugs of black tea daily v. placebo (water, caffeine, milk and sugar) on blood lipids, bowel habit and blood pressure, measured during a run-in period and at the end of weeks 2, 3 and 4 of the test periods. Compliance was established by adding a known amount of p-aminobenzoic acid (PABA) to selected tea bags, and then measuring its excretion in urine. Mean serum cholesterol values during run-in, placebo and on tea drinking were 5.67 (SD 1.05), 5.76 (SD 1.11) and 5.69 (SD 1.09) mmol/l (P = 0.16). There were also no significant changes in diet, LDL-cholesterol, HDL-cholesterol, triacylglycerols, and blood pressure in the tea intervention period compared with placebo. Compared with placebo, stool consistency was softened with tea (P = 0.04), and no other differences were found in bowel habit. Results were unchanged when fifteen 'non-compliers', whose PABA excretion indicated that fewer than six tea bags had been used, were excluded from the analysis, and when differences between run-in and tea periods were considered separately for those who were given tea first or second.

Dietary assessments in the European prospective study of diet and cancer (EPIC).

Biomarkers of nutrition intake were used to validate the dietary assessments proposed for use in the European prospective study of diet and cancer (EPIC). In the UK validation studies, the accuracy of several tested methods was assessed with weighed food records and biomarkers, 24 h urine nitrogen, potassium and plasma carotenoids and vitamin C. Correlations between dietary nitrogen intake from weighed food records and 24 h urine excretion were high (0.78-0.87). The correlations between nitrogen from estimated food diaries and urinary nitrogen were r = 0.60-0.70. Correlations with other methods were lower, but improved by energy adjustment, using residuals for those nutrients correlated with total energy, such as nitrogen and potassium, but not for nutrients not correlated with energy intake--for example, beta-carotene. Hence, the correlation between urinary nitrogen and unadjusted nitrogen from a food frequency questionnaire (FFQ) was 0.24 but improved with energy adjustment to 0.49. UK EPIC uses three methods (diary, improved FFQ and 24 h recall) to assess diet, with repeated measures from the food diary at 18 months and four years. Ninety-three percent of first food diaries are returned completed by participants. Results from 200 subjects randomly selected from the first 2,000 recruits suggest that differences between methods with improved FFQ design are less obvious than in the initial validation study. Results from the diary are more closely correlated with plasma carotenoids and vitamin C than other methods, although supplements of vitamin C are the main determinant of the magnitude of correlations. More detailed biomarker studies are in progress among EPIC participants.

Comparison of metabolic effects of vegetables and teas with colorectal proliferation and with tumour development in DMH-treated F344 rats.

The aim of this study was to screen potentially chemopreventive vegetables and teas for their effects as human dietary components for the colorectal epithelium and also to seek biomarkers of preventive efficacy. Groups of F344 rats were adapted to a human basal diet supplemented with vegetables or teas, having known contents of glucosinolates, polyphenols and anti-oxidants. Both inductions and suppressions were found for overall glutathione S-transferase (GST) and quinone reductase activities. The mitotic index (MI) showed a three-fold range between groups, with substantial reductions by black tea, spinach, petit pois and peppers. Changes to PCNA labelling index and proliferation zone were marginal. No correlation was found between colonic and hepatic enzyme activities, nor with glucosinolate intake. Colonic MI was associated with the activity ratio GST(hepatic)/GST(colonic) (r = 0.49, P < 0.002), possibly reflecting a need for direct induction rather than exposure to products of hepatic conjugation.

Digestion and physiological properties of resistant starch in the human large bowel.

The digestion of four sources of resistant starch (RS) has been studied in twelve healthy volunteers who ate controlled diets for 15 d periods. RS from potato, banana, wheat and maize (17-30 g/d) was compared with a starch-free diet, a diet containing wheat starch that was fully digested in the small intestine, and with 18.4 g NSP from brand/d. RS increased stool wet weight by 1.6 g/d per g RS fed for potato, 1.7 for banana, 2.5 for wheat and 2.7 for maize, but this was significantly less than bran NSP at 4.9 g/g. RS was extensively digested in twenty-seven of thirty-four diet periods but five subjects were unable to break down one or two of the RS sources. Faecal N and energy excretion were increased. RS decreased NSP breakdown and RS2 (resistant starch granules) tended to prolong transit time. All forms of RS increased faecal total short-chain fatty acid excretion. RS2 (from potato and banana) gave greater proportions of acetate in faeces, and RS3 (retrograded starch from wheat and maize) more propionate. We have concluded that RS2 and RS3 are broken down in the human gut, probably in the colon although in 26% of cases this breakdown was impaired. RS exerts mild laxative properties, predominantly through stimulation of biomass excretion but also through some sparing of NSP breakdown.

Does increased endogenous formation of N-nitroso compounds in the human colon explain the association between red meat and colon cancer?

High red meat diets have been linked with risk of sporadic colorectal cancer; but their effects on mutations which occur in this cancer are unknown. G-->A transitions in K-ras occur in colorectal cancer and are characteristic of the effects of alkylating agents such as N-nitroso compounds (NOC). We studied th effect of red meat consumption on faecal NOC levels in eight male volunteers who consumed diets low or high in meat (60 or 600 g/day), as beef, lamb or pork, whilst living in a metabolic suite. Increased intake of red meat induced a significant (P<0.024) 3-fold increase from 40 + or - 7 to ab average of 113 + or - 25 microgram/day NOC, a range of exposure in faeces similar to that from tobacco-specific NOC in cigarette smoke. THe diets were isoenergetic and contained equal amounts of fat, but concentrations of heterocyclic amines were low. Faecal excretion of the promotor ammonia was significantly increased to 6.5 + or - 1.08 mmol/day. When the high red meat diets were supplemented with 20 g phytate-free wheat bran in six volunteers there was no reduction in NOC levels (mean 138 + or - 41 microgram/day NOC), but faecal weight increased. Higher starch and non-starch polysaccharide intakes reduced intraluminal cross-linking in microcapsules (r=-0.77) and reduced faecal pH (r=-0.64). In two volunteers there was no effect of 600 g white meat and fish o faecal NOC (mean low white meat diet 68 + or - 10 microgram/day, high white meat 56 + or -6 microgram/day nor on faecal nitrate, nitrite and iron. Faecal nitrite levels increased on changing from a white to red meat diet (mean high white meat diet 46 + or - 7 mg/day, high red meat diet mean 80 + or - 7 mg/day.) Increased endogenous production of NOC and precursors from increased red meat, but not white meat and fish, consumption may be relevant to the aetiology of colorectal cancer.