Abstract
Atherosclerosis
Atherosclerosis
Both the levels of fat and cholesterol in the diet and its fatty acid composition influence the CAD risk. In recent years, it has been recognized, however, that a high percentage of polyunsaturated fatty acids can have a negative effect, for example on the immune system. It is therefore recommended that 7-10% of dietary energy be consumed in the form of polyunsaturated and saturated fatty acids, but 10-15% as mono-unsaturated fatty acids.
In view of the associated favorable effect on CAD mortality, an increase in consumption of sea fish can now be recommended, while the benefits of consuming high doses of fish oil has not been proven.
The positive effect of a fiber-rich diet is largely due to the associated decrease in consumption of saturated fatty acids. An additional cholesterol-lowering effect has been demonstrated only for particular substances, for example oat bran. Numerous other dietary constituents, such as alcohol, salt or antioxidants, may also have effects on atherogenesis.
[Nutrition and atherosclerosis] Richter-WO. Fortschr-Med. 1995 Jun 10; 113(16): 243-6.
Blood lipids (Oat Bran)
Blood lipids
Sources of dietary fibre can be divided into three groups according to their effect on plasma lipids in humans: (1) a cholesterol-lowering effect demonstrated repeatedly by pectin, guar gum, psyllium and oat bran (sources of soluble fibre); (2) a possible, but not adequate, cholesterol-lowering effect by legumes, barley, rice bran and several types of gum; and (3) those sources that do not lower plasma cholesterol, such as wheat fibre, cellulose and lignin.
Dietary fibre and blood lipids. Truswell-AS. Curr-Opin-Lipidol. 1995 Feb; 6(1): 14-9.
Cholesterol (Rats)
Cholesterol (Rats)
Sources of dietary fiber known to alter cholesterol metabolism and/or bile acid pool size were fed to rats, and activity of the rate-limiting step in bile acid synthesis, cholesterol 7 alpha-hydroxylase, was measured. In the first experiment, semipurified diets containing 5% cellulose, psyllium hydrocolloid, pectin or oat bran as dietary fiber sources or 2% cholestyramine were fed to groups of 10 male Wistar rats for 4 wk.
In the second experiment, groups of six rats were fed diets containing 5% cellulose, rice bran, oat bran or psyllium with and without 0.25% cholesterol. In the first experiment, the activity of cholesterol 7 alpha-hydroxylase (pmol.min-1.mg protein-1) was highest in the cholestyramine-treated group (95.6 +/- 3.6), followed by groups fed psyllium (35.5 +/- 3.5) or pectin (36.0 +/- 4.5), which exhibited more than twice the enzyme activity of groups fed cellulose (16.9 +/- 1.9) or oat bran (12.3 +/- 2.0).
In the second experiment, feeding cholesterol resulted in significantly higher enzyme activity when cellulose (65%), oat bran (118%) and rice bran (60%) were fed, but no difference in activity was observed when cholesterol was added to the psyllium-containing diet. Higher activity of cholesterol 7 alpha-hydroxylase when pectin or psyllium rather than cellulose was fed may explain the almost twofold higher bile acid pool sizes previously reported in response to feeding either of these fibers.
The hypocholesterolemic effect of soluble fibers is modulated through increased synthesis and therefore pool size of bile acids.
Cholesterol 7 alpha-hydroxylase activity is increased by dietary modification with psyllium hydrocolloid, pectin, cholesterol and cholestyramine in rats. Matheson-HB; Colon-IS; Story-JA. J-Nutr. 1995 Mar; 125(3): 454-8.
Lipoproteins (Oat Bran)
Lipoproteins
This study evaluates the possible interaction between chronic oat bran intake and the postmeal metabolic response. Six normolipidemic men consumed three different diets for 14 d, at the end of which they consumed a test meal. The diets were C (control), basal low-fiber diet (15.6 g fiber/d) and a low-fiber (2.8 g fiber) test meal; OB (oat bran), basal low-fiber diet and a 40-g oat bran-enriched test meal (12.8 g fiber); and OB-A (oat bran-adaptation), 14-d oat bran (40 g/d) supplemented diet (23.8 g fiber/d) and an oat bran test meal (12.8 g fiber).
The diets were fed in a random order. Fasting and postmeal blood samples were obtained for 7 h and lipoproteins were isolated.
Adding oat bran to the test meals markedly reduced the postmeal insulin rise (P < 0.05).
Compared with the low-fiber control diet, the effects elicited postprandially by adding oat bran to a single meal were enhanced after 14 d of oat bran feeding, ie, increased plasma triglycerides, phospholipids, and free cholesterol; decreased plasma esterified cholesterol; increased chylomicron and small-sized triglyceride-rich lipoprotein triglycerides; increased LDL and HDL free cholesterol; and decreased HDL esterified cholesterol. Thus, chronic oat bran feeding alters the postmeal response in human subjects.
Chronic oat bran intake alters postprandial lipemia and lipoproteins in healthy adults. Dubois-C; Armand-M; Senft-M; Portugal-H; Pauli-AM; Bernard-PM; Lafont-H; Lairon-D. Am-J-Clin-Nutr. 1995 Feb; 61(2): 325-33.
Proliferation of Colonic Cells
Colonic cell proliferation
The effect of dietary fiber type (cellulose, pectin, or oat bran) on colonic short-chain fatty acids (SCFA), luminal pH, and epithelial cell proliferation was examined in 60 male Sprague-Dawley rats. In vivo cell proliferation was measured by [3H]thymidine incorporation into DNA, pH was measured in vivo, and luminal SCFA were determined by gas chromatography. The pectin and oat bran diets produced higher concentrations of all types of SCFA and total SCFA than cellulose at every site.
The higher the SCFA concentration, the lower was the pH at each site. In the cecum, the concentration of SCFA was positively associated with the number of cells per crypt column (r = 0.961), total cells per crypt (r = 0.963), and the proliferative zone (r = 0.845). In contrast, in the distal colon, there was no significant correlation between SCFA concentration and measurements of cell proliferation. These data suggest that fiber stimulates cecal cell proliferation through the production of SCFA.
The effects of fiber on distal colonic cytokinetics are likely mediated through a different mechanism.
Dietary fibers stimulate colonic cell proliferation by different mechanisms at different sites. Zhang-J; Lupton-JR. Nutr-Cancer. 1994; 22(3): 267-76.
Nine normolipidemic young men consumed a constant diet for 2 mo into which oat bran was incorporated during the second month so that we might test the hypotheses that oats lower serum cholesterol concentrations by decreasing bile acid and fat absorption and increasing bile acid synthesis. Bile acid kinetics were determined by measuring the 13C enrichment of serum cholic and chenodeoxycholic acids.
Oat bran consumption decreased serum cholesterol levels (p < 0.01) and cholic acid pool size (p < 0.05). Deoxycholic acid pool size (p < 0.01) and the synthesis and fractional turnover rates of both primary bile acids (p < 0.05) increased. Total bile acid pool size did not change.
Fecal excretion of total bile acids, the two secondary bile acids and fat increased significantly. The results demonstrate that oat bran lowers serum cholesterol levels in part by altering bile acid metabolism. In addition, the substantial increase in the proportion of the total bile acid pool that was deoxycholic acid is consistent with the hypothesis that oat bran also decreases cholesterol synthesis.
Mechanism of serum cholesterol reduction by oat bran. Marlett-JA; Hosig-KB; Vollendorf-NW; Shinnick-FL; Haack-VS; Story-JA. Hepatology. 1994 Dec; 20(6): 1450-7.
Several studies have indicated that consumption of oat bran lowers blood cholesterol and this effect has been attributed specifically to oat bran's soluble fiber (beta-glucan). This study was designed to test this hypothesis.
The purified fibre (oat gum, 80% beta-glucan) was isolated, and agglomerated in the presence of maltodextrin to facilitate dispersion in a drink. Subjects consumed the oat gum (2.9 g beta-glucan), or maltodextrin placebo, twice daily for 4 weeks, in a randomized, cross-over design with a 3 week wash-out between phases. Consumption was equivalent to a daily dose of about 70 g of oat bran.
The study was with (20) hypercholesterolemic male and female adults and 19 completed, the study.
Blood lipids from fasting individuals were measured weekly throughout the study. Diet was monitored using 3 day food diaries.
There were no significant changes (P > 0.05) in blood lipids during the placebo phase. Mean initial total cholesterol (6.76 +/- 0.13 mmol/l) and low density lipoprotein (LDL) cholesterol (4.59 +/- 0.14 mmol/l) levels fell throughout the oat gum phase, and at week 4 each was reduced 9% relative to initial values (P = 0.0004 and 0.005 respectively). When oat gum was discontinued, total and LDL cholesterol returned to initial levels.
There were no significant changes in high density lipoprotein (HDL) cholesterol. Triglyceride levels also remained unchanged except for a singular decrease at week 4 of the oat gum phase relative to the initial value, but not compared to the placebo value. The lowered mean total and LDL cholesterol levels occurred in the absence of any dietary changes.
The main component of the soluble fibre of oats, beta-glucan, significantly reduced the total and LDL cholesterol levels of hypercholesterolemic adults without changing HDL cholesterol.
Oat beta-glucan reduces blood cholesterol concentration in hypercholesterolemic subjects. Braaten-JT; Wood-PJ; Scott-FW; Wolynetz-MS; Lowe-MK; Bradley-White-P; Collins-MW. Eur-J-Clin-Nutr. 1994 Jul; 48(7): 465-74
LDL Cholesterol
LDL cholesterol
Oat bran fibers might lower total and LDL cholesterol. In a clinical trial, soluble fiber of oat bran slightly lowered total cholesterol and LDL cholesterol levels. There were no major changes in triacylglycerides; HDL cholesterol levels were not significantly influenced by soluble fiber. Oat bran as a dietary supplement may decrease LDL cholesterol levels.
Brown L, Rosner B, Willett WW, Sacks FM: Cholesterol-lowering effects of dietary fiber: a meta-analysis, Am J Clin Nutr 1999 Jan; 69(1): 30-42
High Cholesterol
High cholesterol
Oat bran and psyllium may decrease plasma LDL cholesterol in both normal and hypercholesterolemic individuals. In an eight-week study, normal and hypercholesterolemic individuals ate either psyllium or oat bran, or were in a control group. Plasma LDL cholesterol concentrations decreased by 22.6 to 26% in the psyllium and oat bran groups and 8.4% decrease was found in the control group. Based on these results, oat bran may be an effective dietary supplement in reducing LDL cholesterol.
Romero AL, Romero JE, Galaviz S, Fernandez ML: Cookies enriched with psyllium or oat bran lower plasma LDL cholesterol in normal and hypercholesterolemic men from Northern Mexico, J Am Coll Nutr 1998 Dec; 17(6): 601-8
Colon pH
Colon pH
Oat bran as a dietary fiber may reduce right colonic pH. In a clinical trial, the short-term effect of oat bran on colonic metabolism was evaluated. The trial indicated that the caecal pH was lowered after the trials. Oat bran may impact the pH of the colon.
Naaeder SB, Evans DF, Archampong EQ: Effect of acute dietary fibre supplementation on colonic pH in healthy volunteers, West Afr J Med 1998 Jul-Sep; 17(3): 153-6
Hyperlipidemia
Hyperlipidemia
Oat bran and rice bran may benefit individuals with hyperlipidemia. After a 6-week clinical trial, serum LDL cholesterol declined significantly by 8.3% in the rice starch group and 13% in the rice bran and oat bran groups. Among all groups, triglycerides and HDL-C concentrations were the same.
Gerhardt AL, Gallo NB: Full-fat rice bran and oat bran similarly reduce hypercholesterolemia in humans, J Nutr 1998 May; 128(5): 865-9
Oat Beta Glucan & Immune Function
Oat beta glucan and immune function
Glucan obtained from oats may exhibit the same immune stimulatory effects as glucans from yeast or fungi. Researchers tested the effects of oat beta-glucan (ObetaG) on mouse peritoneal immune cells. ObetaG induced production of IL-1 from macrophages, IL-2, IFN-gamma and IL-4 secretion from cultured spleen cells, and accumulation of leukocytes from a single intraperitoneal administration. ObetaG may therefore stimulate immune activity both in vitro and in vivo.
Estrada A, et al: Immunomodulatory activities of oat beta-glucan in vitro and in vivo, Microbiol Immunol 1997;41(12):991-8
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