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The inherent and diverse capacity of dietary fibres, nondigestible oligosaccharides (NDOs) and prebiotics to modify the gut microbiota and markedly influence health status of the host has attracted rising interest. Research and collective initiatives to determine the composition and diversity of the human gut microbiota have increased over the past decade due to great advances in high-throughput technologies, particularly the 16S ribosomal RNA (rRNA) sequencing. Here we reviewed the application of 16S rRNA-based molecular technologies, both community wide (sequencing and phylogenetic microarrays) and targeted methodologies (quantitative PCR, fluorescent in situ hybridisation) to study the effect of chicory inulin-type fructans, NDOs and specific added fibres, such as resistant starches, on the human intestinal microbiota. Overall, such technologies facilitated the monitoring of microbiota shifts due to prebiotic/fibre consumption, though there are limited community-wide sequencing studies so far. Molecular studies confirmed the selective bifidogenic effect of fructans and galactooligosaccharides (GOS) in human intervention studies. Fructans only occasionally decreased relative abundance of Bacteroidetes or stimulated other groups. The sequencing studies for various resistant starches, polydextrose and beta-glucan showed broader effects with more and different types of gut microbial species being enhanced, often including phylotypes of Ruminococcaceae . There was substantial variation in terms of magnitude of response and in individual responses to a specific fibre or NDO which may be due to numerous factors, such as initial presence and relative abundance of a microbial type, diet, genetics of the host, and intervention parameters, such as intervention duration and fibre dose. The field will clearly benefit from a more systematic approach that will support defining the impact of prebiotics and fibres on the gut microbiome, identify biomarkers that link gut microbes to health, and address the personalised response of an individual's microbiota to prebiotics and dietary fibres.

Whole grains provide a wide range of nutrients and phytochemicals that optimize health. Epidemiologic studies support the protectiveness of whole grain consumption for cardiovascular disease and cancer. Dietary guidance endorses increased whole grains in our diet. A crucial question remaining is the effect of processing of whole grains on their content of nutrients and phytochemicals. Although processing is often considered to be a negative attribute in nutrition, and some forms of processing reduce nutritional value, many factors support the importance of processing of grains to enhance grain consumption. First, whole grains as harvested are generally not consumed directly by humans but require some processing prior to consumption. While refining, that is, removal of the bran and the germ, reduces the nutrient content of grain, milling of grains otherwise concentrates desirable grain components and removes poorly digested compounds and contaminants. Cooking of grains generally increases digestibility of nutrients and phytochemicals. Studies in both animal models and humans support the notion that processed grains are often nutritionally superior to unprocessed grains, probably because of enhanced nutrient bioavailability in processed grains. Processing of grains also provides shelf-stable products that are convenient and good tasting for consumers.

Dietary guidance recommends consumption of whole grains for the prevention of cancer. Epidemiologic studies find that whole grains are protective against cancer, especially gastrointestinal cancers such as gastric and colonic, and hormonally-dependent cancers including breast and prostate. Four potential mechanisms for the protectiveness of whole grains against cancer are described. First, whole grains are concentrated sources of dietary fiber, resistant starch, and oligosaccharides, fermentable carbohydrates thought to protect against cancer. Fermentation of carbohydrates in the colon results in production of short chain fatty acids that lower colonic pH and serve as an energy source for the colonocytes. Secondly, whole grains are rich in antioxidants, including trace minerals and phenolic compounds, and antioxidants have been proposed to be important in cancer prevention. Thirdly, whole grains are significant sources of phytoestrogens that have hormonal effects related to cancer protection. Phytoestrogens are thought to be particularly important in the prevention of hormonally-dependent cancers such as breast and prostate. Finally, whole grains mediate glucose response, which has been proposed to protect against colon and breast cancer.

Dietary guidelines recommend the consumption of whole grains to prevent chronic diseases. Epidemiologic studies support the theory that whole grains are protective against cancer, especially gastrointestinal cancers such as gastric and colon can-cer, and cardiovascular disease. Components in whole grains that may be protective include compounds that affect the gut environment, such as dietary fiber, resistant starch, and oligosaccharides. Whole grains are also rich in compounds that function as antioxidants, such as trace minerals and phenolic compounds, and phytoestrogens, with potential hormonal effects. Other potential mechanisms whereby whole grains may protect against disease include binding of carcinogens and modulation of the glycemic response. Clearly, the range of protective substances in whole grains is impressive and advice to consume additional whole grains is justified. Further study is needed regarding the mechanisms behind this protection so that the most potent protective components of whole grains will be maintained when developing whole grains into acceptable food products for the public.

In an attempt to explain the wide individual variation seen in urinary isoflavonoid phytoestrogen excretion, we conducted a series of 3 human feeding studies: a large cross-sectional study of equol production in humans with a soy challenge, a comparison of phytoestrogen metabolism when subjects consumed fermented and unfermented soy products, and a dose-response study of urinary isoflavonoid excretion at the low end of soy consumption. All studies were conducted in young, healthy humans. Urinary isoflavonoids were measured by isotope-dilution gas chromatography-mass spectrometry. Similar to results from other studies, 35% of screened subjects (30 men and 30 women) excreted equol (>2000 nmol/d). In women, equol excretion was associated with higher intake of dietary fiber and carbohydrate. Fermentation of soy decreased the isoflavone content of the product fed but increased the urinary isoflavonoid recovery, suggesting that fermentation increases availability of isoflavones in soy. When soy-protein powder was fed at 0, 5, 10, and 20 g/d (0-36 mg isoflavones), there was a linear dose response of urinary isoflavonoid excretion to soy consumption that did not differ between subjects with high and low equol excretion. These results suggest that equol excretion may be related to the fermentable carbohydrate content of the diet; additional study is needed. Processing of soy affects isoflavone metabolism and must be considered in recommending exposure to isoflavones from soyfoods. Although optimal isoflavone exposure for disease protection has not been determined, urinary isoflavonoid excretion appears linear at low-to-moderate soy consumption.

Epidemiological studies have demonstrated that diets high in vegetables and fruit are associated with a decreased risk of cancer and, possibly cardiovascular disease. Certain constituents of vegetables and fruit inhibit the in vitro activity of platelet-derived growth factor (PDGF), a potent mitogen implicated in both cancer and cardiovascular disease. Few studies have measured PDGF in relationship to diet in vivo. Specifically, there are no data regarding the changes in PDGF levels of mitogenic activity after a dietary intervention. In this study, 19 young, healthy individuals consumed four (9-day) experimental diets in random order: (a) control diet alone; (b) control diet plus carotenoid-rich vegetables; (c) control diet plus cruciferous vegetables; and (d) control diet plus soy foods. Compared to the control diet, there was a significant elevation in PDGF-AB serum levels when the individuals were consuming the soy diet (P = 0.016). Increased PDGF-AB levels were also noted for the carotenoid diet. There was no change from baseline levels when individuals were consuming the cruciferous diet. Overall, mitogenic activity did not change on any of the experimental diets. This study suggests that high soy and carotenoid diets increase serum levels of PDGF-AB. This may represent an additional mechanism by which diet influences individual risk of cancer; further investigation into the role of diet and growth factors is warranted.

Urinary lignan and isoflavonoid excretion were examined in 11 men and 9 women consuming four nine-day controlled experimental diets: basal (vegetable free), carotenoid vegetable (carrot and spinach), cruciferous vegetable (broccoli and cauliflower), and soy (tofu and textured vegetable protein product). Three-day urine collections (Days 7-9) were analyzed for lignans and isoflavonoids with use of isotope-dilution gas chromatography-mass spectrometry. Urinary excretion of the lignans enterodiol and enterolactone was higher during the carotenoid and cruciferous vegetable diets than during the basal diet (p = 0.0001), suggesting that these vegetables may provide a source of mammalian lignan precursors. Urinary excretion of the isoflavonoids equol, O-desmethylangolensin, daidzein, and genistein was higher when subjects consumed soy diets than when they consumed the other test diets (p < 0.02). Gender differences in lignan excretion were observed. Men excreted more enterolactone (p = 0.006) and less enterodiol (p = 0.013) than women, implying a gender difference in colonic bacterial metabolism of lignans. There was no effect of gender on isoflavonoid excretion.

Higher intakes of vegetables and fruits are associated with a lower risk of certain human cancers. A biomarker of vegetable and fruit intake would be a valuable research tool. A cross-sectional study assessed the association between plasma carotenoid concentrations and intakes of vegetables and fruits. Plasma carotenoids (alpha-carotene, beta-carotene, lutein, beta-cryptoxanthin, and lycopene) were measured in 50 male and 49 female participants, aged 18-37 years, with a wide range of habitual vegetable and fruit intakes. Dietary intakes were assessed via a food frequency questionnaire. Intake of vegetables and fruits and high carotenoid foods were measured. The sum of the plasma carotenoids (excluding lycopene) was highly correlated with intake of total vegetables and fruits (r = 0.59). Of the individual plasma carotenoids, plasma alpha-carotene had the highest correlation with intakes of both total vegetables (r = 0.50) and total fruits (r = 0.58). Intakes of foods with high carotenoid contents were correlated with their corresponding plasma concentrations as follows: high beta-carotene foods (r = 0.41); high lutein foods (r = 0.46); and high lycopene foods (r = 0.11). Multiple regression analyses showed that intake of total vegetables and fruits was the most significant determinant of each plasma carotenoid except lycopene. The utility of combining the plasma carotenoids as biomarkers of vegetable and fruit intake was assessed by a stepwise regression of total vegetable and fruit intake on plasma carotenoids. Significant determinants of intake of total vegetables and fruits were alpha-carotene, beta-cryptoxanthin, lutein, and energy intake (R2 = 0.53).(ABSTRACT TRUNCATED AT 250 WORDS)

Lignans and isoflavonoid phytoestrogens, produced from plant precursors by colonic bacteria, may protect against certain cancers. We examined the effects of flaxseed consumption on urinary lignans and isoflavonoids. Eighteen women consumed their usual omnivorous diets for three menstrual cycles and their usual diets supplemented with flaxseed powder (10 g/d) for three cycles in a randomized crossover design. Three-day urine samples from follicular and luteal phases were analyzed for lignans and isoflavonoids by isotope-dilution gas chromatography--mass spectrometry. Excretion of the lignans enterodiol and enterolactone increased with flaxseed from 1.09 +/- 1.08 and 3.16 +/- 1.47 to 19.48 +/- 1.10 and 27.79 +/- 1.50 mumol/d, respectively (P < 0.0002). Enterodiol and enterolactone excretion varied among subjects in response to flaxseed (3- to 285-fold increase). There were no differences in excretion of isoflavonoids (daidzein, genistein, equol, and O-desmethylangolensin) or the lignan matairesinol with flaxseed. Excretion was not altered by phase of menstrual cycle or duration of flaxseed consumption.

Current dietary advice suggests consumers increase consumption of whole-grain products because of their potential role in prevention of chronic disease. Whole grains are important sources of nutrients that are in short supply in our diet, including dietary fiber, resistant starch, trace minerals, certain vitamins, and other compounds of interest in disease prevention, including phytoestrogens and antioxidants. Despite dietary recommendations to increase intake of whole grains, little epidemiological evidence is available to support the physiological importance of whole-grain intake. Most epidemiological studies focus on nutrients, rather than whole foods, so little attempt has been made to evaluate the contribution of whole grains in disease. Further, studies on vegetarians that show decreased risk of degenerative diseases are unable to separate the contribution of fruit and vegetable intake when compared with whole-grain intake and protection from disease. The few epidemiological studies that have evaluated a role for whole grains suggest that they have an important role in disease prevention and deserve more study.

Lignans are a group of phytochemicals shown to have weakly estrogenic and antiestrogenic properties. Two specific lignans, enterodiol and enterolactone, are absorbed after formation in the intestinal tract from plant precursors particularly abundant in fiber-rich food and are excreted in the urine. We evaluated the effect of the ingestion of flax seed powder, known to produce high concentrations of urinary lignans, on the menstrual cycle in 18 normally cycling women, using a balanced randomized cross-over design. Each subject consumed her usual omnivorous, low fiber (control) diet for 3 cycles and her usual diet supplemented with flax seed for another 3 cycles. The second and third flax cycles were compared to the second and third control cycles. Three anovulatory cycles occurred during the 36 control cycles, compared to none during the 36 flax seed cycles. Compared to the ovulatory control cycles, the ovulatory flax cycles were consistently associated with longer luteal phase (LP) lengths (mean +/- SEM, 12.6 +/- 0.4 vs. 11.4 +/- 0.4 days; P = 0.002). There were no significant differences between flax and control cycles for concentrations of either estradiol or estrone during the early follicular phase, midfollicular phase, or LP. Although flax seed ingestion had no significant effect on LP progesterone concentrations, the LP progesterone/estradiol ratios were significantly higher during the flax cycles. Midfollicular phase testosterone concentrations were slightly higher during flax cycles. Flax seed ingestion had no effect on early follicular phase concentrations of DHEA-S, PRL, or sex hormone-binding globulin. Our data suggest a significant specific role for lignans in the relationship between diet and sex steroid action, and possibly between diet and the risk of breast and other hormonally dependent cancers.

This study compared the bowel function, fecal hemoglobin (Hb) loss, iron status and diets of 36 women of varying activity levels. In addition, we examined the effect of a marathon race on bowel function and fecal Hb loss in 15 of these women. The subjects were divided into 4 groups based on estimated daily exercise energy expenditure: Group A) less than 400 kcal/d (less than 1674 kJ/d); Group B) 400-599 kcal/d (1674-2507 kJ/d); Group C) 600-800 kcal/d (2511-3348 kJ/d); and Group D) greater than 800 kcal/d (greater than 3348 kJ/d). There were no differences in hematological and iron indexes among the 4 groups. Mean daily stool wet weights and individual stool weights were greater for groups B and D as compared to group A. However, transit time and frequency of defecation were not different. Daily fecal Hb losses (mg/day) were greater in groups B, C, and D as compared to A, but there was no difference in fecal Hb concentrations (mg/g feces) among the groups. Dietary intakes of energy, protein, fat and fiber were similar for all groups. Ascorbic acid and iron intakes from food significantly increased with increased estimated daily energy expenditure. Total intakes of ascorbic acid and iron, including oral supplements, were not different among the groups. Marathon racing resulted in a 21% increase in mean transit time, a 27% decrease in daily stool weight and 21% lower frequency of defecation. Fecal Hb concentrations and daily Hb losses before and after the race were not significantly different, despite an increased daily Hb loss in 10 of the 15 runners after the race.(ABSTRACT TRUNCATED AT 250 WORDS)