The food matrix of spinach is a limiting factor in determining the bioavailability of beta-carotene and to a lesser extent of lutein in humans.
Carotenoid bioavailability depends, amongst other factors, on the food matrix and on the type and extent of processing. To examine the effect of variously processed spinach products and of dietary fiber on serum carotenoid concentrations, subjects received, over a 3-wk period, a control diet (n = 10) or a control diet supplemented with carotenoids or one of four spinach products (n = 12 per group): whole leaf spinach with an almost intact food matrix, minced spinach with the matrix partially disrupted, enzymatically liquefied spinach in which the matrix was further disrupted and the liquefied spinach to which dietary fiber (10 g/kg wet weight) was added. Consumption of spinach significantly increased serum concentrations of all-trans-beta-carotene, cis-beta-carotene, (and consequently total beta-carotene), lutein, alpha-carotene and retinol and decreased the serum concentration of lycopene. Serum total beta-carotene responses (changes in serum concentrations from the start to the end of the intervention period) differed significantly between the whole leaf and liquefied spinach groups and between the minced and liquefied spinach groups. The lutein response did not differ among spinach groups. Addition of dietary fiber to the liquefied spinach had no effect on serum carotenoid responses. The relative bioavailability as compared to bioavailability of the carotenoid supplement for whole leaf, minced, liquefied and liquefied spinach plus added dietary fiber for beta-carotene was 5.1, 6.4, 9.5 and 9.3%, respectively, and for lutein 45, 52, 55 and 54%, respectively. We conclude that the bioavailability of lutein from spinach was higher than that of beta-carotene and that enzymatic disruption of the matrix (cell wall structure) enhanced the bioavailability of beta-carotene from whole leaf and minced spinach, but had no effect on lutein bioavailability. (+info
Modulation of distal colonic epithelial barrier function by dietary fibre in normal rats.
BACKGROUND: Dietary fibre influences the turnover and differentiation of the colonic epithelium, but its effects on barrier function are unknown. AIMS: To determine whether altering the type and amount of fibre in the diet affects paracellular permeability of intestinal epithelium, and to identify the mechanisms of action. METHODS: Rats were fed isoenergetic low fibre diets with or without supplements of wheat bran (10%) or methylcellulose (10%), for four weeks. Paracellular permeability was determined by measurement of conductance and 51Cr-EDTA flux across tissue mounted in Ussing chambers. Faecal short chain fatty acid (SCFA) concentrations were assessed by gas chromatography, epithelial kinetics stathmokinetically, and mucosal brush border hydrolase activities spectrophotometrically. RESULTS: Body weight was similar across the dietary groups. Conductance and 51Cr-EDTA flux were approximately 25% higher in animals fed no fibre, compared with those fed wheat bran or methylcellulose in the distal colon, but not in the caecum or jejunum. Histologically, there was no evidence of epithelial injury or erosion associated with any diet. The fibres exerted different spectra of effects on luminal SCFA concentrations and pH, and on mucosal indexes, but both bulked the faeces, were trophic to the epithelium, and stimulated expression of a marker of epithelial differentiation. CONCLUSIONS: Both a fermentable and a non-fermentable fibre reduce paracellular permeability specifically in the distal colon, possibly by promoting epithelial cell differentiation. The mechanisms by which the two fibres exert their effects are likely to be different. (+info
The influence of a diet rich in wheat fibre on the human faecal flora.
The effect on the faecal flora of adding wheat fibre to a controlled diet in four healthy volunteers for a 3-week period has been observed. No change in the concentration of the bacteria in the bacterial groups counted was found, although there was a slight increase in total output associated with increased faecal weight. The predominant organisms in all subjects were non-sporing anaerobes, but the dominant species in each subject was different and was unaffected by changing the diet. Similarly, the concentration of faecal beta-glucuronidase detected in two subjects was unaltered and the concentration of clostridia able to dehydrogenate the steroid nucleus found in one subject was unaltered. It is suggested that the faecal microflora is not primarily controlled by the presence of undigested food residues in the large bowel. (+info
Fermentation substrate and dilution rate interact to affect microbial growth and efficiency.
The effect of dilution rate (D) on carbohydrate, fibrous and nonfibrous, and protein fermentation by ruminal microorganisms was studied using a single-effluent continuous-culture system. The diets of fibrous carbohydrate, nonfibrous carbohydrate, or protein were formulated with soybean hulls (FC), ground corn (NFC), or isolated soy protein (PR) as the primary ingredient, respectively. Six dilution rates (.025, .050, .075, .10, .15, and .20/h of fermenter volume) were used. Digestibilities of DM, OM, and CP for the three diets and of NDF and ADF for the FC diet decreased (P<.001) as D increased, although the response of the digestibility to D varied with diet. Increasing D resulted in an increase in pH (P<.001) and a decrease (P<.001) in ammonia concentration. Daily volatile fatty acid production increased (quadratic; P<.01) for the FC and NFC diets, but decreased (quadratic; P<.001) for the PR diet. Increasing D quadratically increased (P<.001) the molar percentage of acetate and propionate, but quadratically decreased (P<.001) butyrate and valerate for the FC and NFC diets. For the PR diet, the molar percentage of propionate and valerate increased (quadratic; P<.01), whereas acetate and butyrate decreased (linear; P<.001) in response to increasing D. Molar percentage of isobutyrate and isovalerate decreased (P<.01) with increasing D for all three diets. As D increased, daily microbial N production showed quadratic responses with maximum values achieved at .126, .143, and .187/h D for the FC, NFC, and PR diet, respectively. There was a positive correlation between microbial growth efficiency (MOEFF) and D. A quadratic model fit the data of MOEFF as affected by D, and maximum MOEFF of 37.3, 59.6, and 71.4 g of bacterial N/kg OM truly fermented were calculated to be achieved at .177, .314, and .207/h D for the FC, NFC, and PR diet, respectively. Dilution rate significantly influenced the ruminal microbial fermentation of fibrous and nonfibrous carbohydrates and proteins, and was positively related to microbial yield and growth efficiency. In addition, microbial nitrogen composition, and therefore efficiency, was affected by substrate fermented. (+info
Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial.
BACKGROUND: Currently there is considerable interest in the potential health benefits of oil seeds, such as soy and flaxseed, especially in relation to cardiovascular disease and cancer. OBJECTIVE: We therefore evaluated health aspects of partially defatted flaxseed in relation to serum lipids, indicators of oxidative stress, and ex vivo sex hormone activities. DESIGN: Twenty-nine hyperlipidemic subjects (22 men and 7 postmenopausal women) completed two 3-wk treatment periods in a randomized, crossover trial. Subjects were given muffins that contributed approximately 20 g fiber/d from either flaxseed (approximately 50 g partially defatted flaxseed/d) or wheat bran (control) while they consumed self-selected National Cholesterol Education Program Step II diets. Both muffins had similar macronutrient profiles. Treatment phases were separated by > or = 2 wk. RESULTS: Partially defatted flaxseed reduced total cholesterol (4.6+/-1.2%; P = 0.001), LDL cholesterol (7.6+/-1.8%; P < 0.001), apolipoprotein B (5.4+/-1.4%; P = 0.001), and apolipoprotein A-I (5.8+/-1.9%; P = 0.005), but had no effect on serum lipoprotein ratios at week 3 compared with the control. There were no significant effects on serum HDL cholesterol, serum protein carbonyl content, or ex vivo androgen or progestin activity after either treatment. Unexpectedly, serum protein thiol groups were significantly lower (10.8+/-3.6%; P = 0.007) at week 3 after the flaxseed treatment than after the control, suggesting increased oxidation. CONCLUSIONS: These data indicate that partially defatted flaxseed is effective in lowering LDL cholesterol. No effects on lipoprotein ratios, ex vivo serum androgen or progestin activity, or protein carbonyl content were observed. The significance of increased oxidation of protein thiol groups with flaxseed consumption requires further investigation. (+info
Human metabolism of mammalian lignan precursors in raw and processed flaxseed.
BACKGROUND: The mammalian lignans enterolactone and enterodiol are produced in the colon by the action of bacteria on the plant precursor secoisolariciresinol diglycoside, which is found in high concentrations in flaxseed. OBJECTIVE: Two experiments were conducted to determine 1) whether there is a dose response in urinary lignan excretion with increasing flaxseed intake, 2) whether flaxseed processing affects lignan excretion, 3) peak plasma lignan concentrations, and 4) plasma lignan concentrations after chronic supplementation. DESIGN: Nine healthy young women supplemented their diets with 5, 15, or 25 g raw or 25 g processed (muffin or bread) flaxseed for 7 d during the follicular phase of their menstrual cycles. Twenty-four-hour urine samples were collected at baseline and on the final day of supplementation. As an adjunct to the 25-g-flaxseed arm, subjects consumed the supplement for an additional day and blood and urine samples were collected at specific intervals. All blood and urine samples were analyzed for enterolactone and enterodiol by gas chromatography-mass spectroscopy. RESULTS: A dose-dependent urinary lignan response to raw flaxseed was observed (r = 0.72, P < 0.001). The processing of flaxseed as a muffin or bread did not affect the quantity of lignan excretion. Plasma lignan concentrations were greater (P < or = 0.05) than baseline by 9 h after flaxseed ingestion (29.35+/-3.69 and 51.75+/-7.49 nmol/L, respectively). The total plasma area under the curve was higher on the eighth than on the first day (1840.15+/-343.02 and 1027.15+/-95.71 nmol x h/L, respectively). CONCLUSION: Mammalian lignan production from flaxseed precursors is dependent on time and dose but not on processing. (+info
Supplemental cracked corn for steers fed fresh alfalfa: I. Effects on digestion of organic matter, fiber, and starch.
The effect of supplementation with different levels of cracked corn on the sites of OM, total dietary fiber (TDF), ADF, and starch digestion in steers fed fresh alfalfa indoors was determined. Six Angus steers (338 +/- 19 kg) fitted with cannulas in the rumen, duodenum, and ileum consumed 1) alfalfa (20.4% CP, 41.6% NDF) ad libitum (AALF); 2), 3), and 4) AALF supplemented (S) with .4, .8, or 1.2%, respectively, of BW of corn; or 5) alfalfa restricted at the average level of forage intake of S steers (RALF), in a 5 x 5 Latin square design. Total OM intake was lower (P < .01) in steers fed RALF than in those fed AALF but level of forage intake did not affect sites of OM, TDF, or starch digestion (P > .05). Forage OM intake decreased (P < .01) linearly (8,496 to 5,840 g/d) but total OM intake increased (P = .03) linearly (8,496 to 9,344 g/d) as corn increased from .4 to 1.2% BW. Ruminal apparent and true OM disappearance was not affected, but OM disappearing in the small intestine increased (P < .01) linearly with increasing levels of corn. Total tract OM digestibility (71.2 to 76.2%) and the proportion of OM intake that was digested in the small intestine (15.4 to 24.5%) increased (P < .01) linearly as corn increased. The TDF and ADF intakes decreased (P < .01) linearly as level of corn increased. Total tract TDF and ADF digestibilities were not different among treatments (average 62.9 and 57.8%, respectively). Starch intake and starch digested in the rumen and small and large intestine increased (P < .01) linearly with increasing corn level. Ruminal pH and VFA concentrations decreased and increased (P < .01), respectively, with increasing corn. Supplementation with corn increased OM intake, decreased forage OM intake, and increased the proportion of OM that was digested in the small intestine, but fiber digestion was not affected. (+info
Fractionation of fiber and crude protein in fresh forages during the spring growth.
The composition of the fiber and CP of alfalfa, bromegrass, and endophyte-free and -infected tall fescue forages was compared during the spring growth from vegetative to reproductive stages. Forages were sampled from April 27 to June 6 in 1994, and from April 27 to June 11 in 1995, with 11 and 12 harvest dates, respectively. Total dietary fiber (TDF) was fractionated into insoluble and soluble fiber (SF). The CP of the forages was fractionated into nonprotein N (A), soluble CP (B1), insoluble CP that was soluble in neutral detergent (B2), CP insoluble in neutral detergent but soluble in acid detergent (B3), and CP insoluble in acid detergent (C). Effects of year, forage species, and harvest dates (day as a covariable) were included in the model. Across harvest dates, alfalfa (A) had lower (P < .01) TDF and higher (P < .01) SF concentrations than grasses (GR) (A: 49.9 and 14.4% and GR: 60.4 and 4.5% [OM basis] for TDF and SF, respectively). Alfalfa had higher (P < .01) CP (20.6% DM) than GR (15.3%). The rate of decrease in CP (% DM) across days was higher (P < .01) for bromegrass (-.4%/d) than for the other forages (-.29%/d). Fraction A (% of CP) was not different (P = .24) among forages (22.5%), but B1 was higher (P < .01) in A (17.1%) than in GR (13.2%). The B2 fraction (% of CP) was higher (P < .01) in A compared with GR (51.6 vs 45.9%, respectively). Alfalfa had lower (P < .01) B3 (3.0% of CP) than bromegrass (18.6%) and tall fescue (13.2%). Fraction C was not different (P = .23) among forages (3.8%). Fractions A, B1, and C (% of CP) did not change (P > .05) across days for all forages. Fraction B2 (% of CP) decreased across days in A (-.21%/d) but was not affected in GR. Fraction B3 (% of CP) increased (P < .05) in A (.1%/d), decreased in endophyte-infected tall fescue (-.20%/d), and did not change (P > .05) in the other forages. Crude protein and fiber composition were affected more by forage species than by maturity. The CP and NDF concentrations were more affected by maturity. Insoluble fractions but not soluble fractions of CP were affected by maturity. (+info