Effect of dietary fat and fiber on fecal flora, bacterial metabolites, and fecal properties in Japanese volunteers.

The effects of dietary fat and dietary fiber (DF) levels in diet on fecal flora, activities of three fecal enzymes, putrefactive metabolites, fecal mutagenicity and fecal properties were studied in eight healthy volunteers. They were given low fat and low DF diet (LF: fat energy ratio was 13.9%, and DF intake was 9.0 g/day) for 10 days, high fat and low DF diet (HF: fat energy ratio was 52.7%, and DF intake was 7.1 g/day) for 10 days, and high fat and high DF diet (HFF: fat energy ratio was 52.0%, and DF intake was 24.8 g/day) for 10 days. No change of fecal flora at the bacterial group level was observed throughout the experimental period, except that the population of lactobacilli showed a tendency to increase in HF period. Fecal activities of beta-glucuronidase, beta-glucosidase and nitroreductase and some putrefactive products were unchanged between LF and HF, while these values decreased in HFF period. No significant change of fecal properties was observed between LF and HF, while by HFF supplementation fecal weight increased and fecal pH value was lower than that in LF and HF. Excretions of iron, zinc and calcium in feces did not increase by high DF supplementation.     

Effect of low-fat, high-carbohydrate, high-fiber diet on fecal bile acids and neutral sterols

The effect of a diet low in total fat and high in complex carbohydrates on the excretion of bile acids and neutral sterols and on serum lipids was studied in women, 46-47 years old, who were consuming a mixed Western diet. Participants kept an initial 3-day food record while consuming their normal diet (pre-diet period). During the dietary intervention period (experimental diet) which lasted for 26 days, all volunteers consumed a low-calorie, low-fat (less than 10% of total calories), high-fiber (37 g/day, high-carbohydrate diet. At the 1-year follow-up, the participants completed another 3-day food record, which indicates that these volunteers maintained their caloric and fat intake at levels slightly higher than the experimental diet, but lower than the pre-diet period. Individual 24-hr fecal samples for 2 days and blood samples were collected from the volunteers during each dietary period. Fecal samples were analyzed for neutral sterols and bile acids, and blood samples were analyzed to ascertain cholesterol and triglyceride levels. There were no significant differences in the excretion of neutral sterols between the dietary periods. Fecal secondary bile acids were significantly lower during the experimental and follow-up diet periods compared with the pre-test diet period. Serum cholesterol levels were significantly lower during the experimental and follow-up diet periods than during the pre-test diet period. These results suggest that switching from a high-fat, low-fiber diet to a low-fat, high-fiber diet can reduce the excretion of bile acids which are thought to be involved in the promotion of colon cancer.     

Effects of dietary fiber from wheat, corn, and soy hull bran on excretion of fecal bile acids in humans

Effects of dietary fiber on bile acid excretion and fecal bile acid concentration have been studied for seven subjects fed 26 g of either soft white wheat bran, corn bran, soybean hulls, or hard red spring wheat bran. Results indicate that even in a controlled study using a metabolic word, individual subject variation has a major impact on fecal bile acid excretion. This observation has not been fully appreciated in previous human studies. No significant change in the composition of fecal bile acids could be associated with the decrease in serum lipid levels previously reported. A method for the isolation and quantitation of fecal bile acids is described which does not require purification by thin-layer chromatography. A preliminary study of lyophilized fecal samples stored at -10 to -30 degrees C showed very little or no change in bile acid content. Samples stored at room temperatures for 11 months showed a substantial reduction in bile acid content.     

Effect of dietary fat composition on rat colon plasma membranes and fecal lipids

The present study was designed to examine the effect of dietary fat composition on the structure of colon mucosal plasma membranes and fecal lipids. Rats were fed a purified diet containing 14% of either highly saturated fat (beef fat or butterfat) or highly polyunsaturated oil (safflower) in addition to 2% corn oil for 4 wk. Colon mucosal membranes were prepared and examined for lipid composition and protein pattern. Saturated fatty acid feeding resulted in the loss of some protein bands from plasma membranes compared to feeding polyunsaturated fatty acids. Within the saturated fatty acid--rich fats, feeding beef fat caused a greater loss than did feeding butterfat. Dietary fat composition had no effect on membrane content of phospholipid and cholesterol. Saturated fatty acid feeding resulted in an increase in the percentage of 18:1 in plasma membrane lipids compared to feeding safflower oil. The observed changes in the structure of colon mucosal membrane of animals fed the saturated fats were associated with an increase in fecal free fatty acids. There was a 4-fold and 2-fold increase in fecal free fatty acids with feeding the beef fat and butterfat diets, respectively, compared to the safflower oil diet. Alterations in fecal bile acid and free fatty acid composition were also noticed with feeding saturated fatty acids. The results obtained suggest that feeding saturated fatty acids as the main source of fat in the diet could influence the structure of colon mucosa, and this could be mediated through fecal free fatty acids.     

Changes in small intestinal digestive enzyme activity and bile acids with dietary cellulose in rats

Rats were fed semipurified diets which contained either 20% cellulose, Solka Floc, (HF) or no fiber (C) for 10 days. In the intestinal contents, the HF group had lower activity per milligram contents of trypsin, chymotrypsin, amylase, lipase and total proteolytic activity. Total activity of enzymes in the intestinal contents was also lower, except for chymotrypsin and leucine amino peptidase. Bile acid levels per milligram were lower in the HF group but the total amount was greater. The total weight of intestinal contents was greater in the HF group and total amount of protein present was elevated. The results indicate that a source of dietary fiber, cellulose, can affect the availability of enzymes and bile acids in the small intestine.     

Colon cancer and dietary fiber: cellulose inhibits the DNA-damaging ability of bile acids

Colon cancer is the second most common type of cancer in the United States. Bile acids have been implicated in the etiology of this disease. In a previous study, we showed that bile acids can damage DNA in vitro. In this study, we report that this damage is largely prevented when the bile acids are pretreated with cellulose fiber. Preliminary data show that cellulose may act as a catalyst to promote polyesterification of bile acid to a biologically inactive form.     

Effect of dietary fat on opiate receptor binding and body composition in mice

C57BL/6 and C3H male mice were fed either a 25% corn oil, 25% butter fat, or chow diet ad libitum for 6 weeks. At that time, opiate receptor binding in the brain and body composition was determined. Regardless of the type of dietary fat, both groups fed with high-fat diets in each strain of mice exhibited obesity in the absence of hyperphagia as compared with their chow-fed counter-parts. Scatchard analysis of opiate receptor binding from the brains of C57BL/6 mice fed with the polyunsaturated fat diet (corn oil) demonstrated a decreased K_D relative to the saturated fat-fed group with no significant difference in B_max. The C3H mice exhibited no significant differences in either binding affinity or receptor number within the three dietary groups. Fatty acid analysis of the synaptic plasma membrane showed changes in the C18:1 ω-9, C18:2 ω-6, and C22:6 ω-3 fatty acid composition. C18:1 ω-9 was elevated while C22:6 ω-3 was depressed in corn oil compared to butter fat-fed C57BL/6 mice. There were no differences in membrane fluidity as measured by fluorescence polarization.     

Plasma lipids, lipoproteins, and fecal excretion of neutral sterols and bile acids in rats fed various high fat diets or a low fat/high sucrose diet

The effect of feeding various diets on plasma lipids and lipoproteins and on fecal excretion of neutral sterols and bile acids was studied in rats fed for 7 wk diets containing 42% of energy as either coconut oil (CO), sunflower seed oil (SO), fish body oil (FBO), cod liver oil (CLO), or a low fat/high sucrose diet (SU). Triacylglycerols (TG) in whole plasma and VLDL + LDL were lower in rats fed high amounts of polyunsaturated fatty acids (PUFA) than in those fed the CO diet. Plasma HDL2 components in FBO and CLO groups were generally lower than in the other groups. Percentages of liver and heart linoleic and arachidonic acid were higher in the SO group, but lower in groups fed marine oils, than in the CO group. There was a high relative amount of eicosapentaenoic and docosahexaenoic acid in liver and heart of rats fed marine oils. Fecal excretion of bile acids was lower in the PUFA groups than in the CO group, whereas the sum of neutral sterols was similar in all groups. Plasma HDL2 (and VLDL + LDL) correlated positively, but HDL3 negatively, with fecal bile acid excretion. Accordingly, increased bile acid excretion does not seem to account for hypolipemia following intake of PUFA diets.     

Effects of dietary cellulose, psyllium husk and cholesterol level on fecal and colonic microbial metabolism in monkeys

The effect of long-term feeding of dietary fiber and two levels of cholesterol on monkey colonic microbial metabolism was studied. Three groups of African green monkeys were fed for 3.5 yr purified diets containing 9.7% cellulose or psyllium husk and 0.8 mg cholesterol per kcal or 9.7% cellulose and 0.1 mg cholesterol per kcal. Total viable anaerobe and aerobe counts, microbial beta-glucuronidase activity, volatile fatty acid and ammonia nitrogen concentrations, dry matter and pH were determined in fecal and colonic samples. Compared to cellulose, psyllium husk feeding decreased (P less than 0.05) percentage dry matter, beta-glucuronidase (EC 3.2.1.31) activity and pH, and increased (P less than 0.05) ammonia nitrogen and volatile fatty acid output in feces and in colon contents. In all groups, colonic beta-glucuronidase activity was greater (P less than 0.05) than in fecal samples. Microbial beta-glucuronidase activity, pH or percentage dry matter in the ascending colon was not different from that in the transcending or descending segments. The ratio of anaerobic to aerobic bacteria was lower in colon contents from monkeys fed psyllium husk compared to those fed cellulose. Total viable bacterial counts were lower in monkeys fed low cholesterol compared to high cholesterol diets. The results suggest that chronic intake of dietary psyllium husk resulted in greater colonic microbial metabolism compared to cellulose feeding.     

Effect of soy protein, casein and trypsin inhibitor on cholesterol, bile acids and pancreatic enzymes in mice

Dietary vegetable proteins may lower plasma cholesterol compared to animal proteins. We considered the possibility that lower digestibility and the trypsin inhibitor (TI) content of plant proteins could lead to alterations in bile acid metabolism and exocrine pancreatic function mediating some of this change. Mice were fed cholesterolemic diets of different protein source and TI content: casein, soy protein isolate, or casein plus TI for 4 weeks. Plasma and liver cholesterol were measured; pancreata, intestinal contents and mucosal scrapes were collected for bile acid, trypsin, chymotrypsin, amylase, and lipase assays. The soy group had lower plasma cholesterol levels. Intestinal bile acids in this group were higher, suggesting a causal relationship (increased bile acid secretion leading to increased cholesterol catabolism). Conversely, liver cholesterol in this group was raised, reflecting a possible shift in body cholesterol pools. TI addition did not affect lipid metabolism, though it did affect pancreatic function: it led to increased pancreatic weight and depressed intestinal trypsin activity, but elevated chymotrypsin and amylase levels in pancreas and intestine and increased trypsin levels in the pancreas. Therefore, soybean TI does not seem to affect cholesterol metabolism, though it greatly affects pancreatic secretion. On the other hand, soy protein has a marked effect on the bile acid and cholesterol metabolism, which may be a function of protein quality.     

Analysis of fecal bile acids and diet among the Japanese in Hawaii

Fecal samples of 165 Japanese men in Hawaii, age 43 to 74, were analyzed for bile acid content by their conversion to the methyl ester and the trimethylsilyl ether derivative followed by separation on a gas chromatograph. The arithmetic mean of total bile acids for the 165 specimens was 10.96 mg/g dry weight feces. Each of the following bile acids was detectable in over 77% of the fecal specimens: cholic, deoxycholic, lithocholic, and cholanic acid. The intake of Western foods was not positively correlated with the fecal content of secondary or modified bile acids, even though other workers have observed that these bile acids predominated in persons from Westernized countries. Two of the Japanese foods were negatively correlated with the levels of modified bile acids, which suggested that these foods contributed to a decrease in modified bile acids in fecal specimens. Fecal bile acid measurements appeared to be associated with age, but not with weight, height, or serum cholesterol levels.     

Dietary fiber supplementation and fecal bile acids, neutral steroids and divalent cations in rats

Young adult rats were fed ad libitum for 4 wk on defined diets containing either no fiber, 10% levels of insoluble fiber sources [cellulose, wheat bran, alfalfa, mixed fibers (Fibyrax)], 5% levels of soluble fiber sources [pectin, guar gum, psyllium (Metamucil)] or 2% cholestyramine (Questran), a bile acid sequestrant. Fecal samples were obtained from paired rats over a 3-d period, were analyzed for neutral and acidic steroid levels and compositions and, together with the food, were assayed for divalent cations (Ca2+, Mg2+, Fe2+ and Zn2+). Animals in all groups were in balance for divalent cations, and there appeared to be no relationship between the extent of cation balance and the type of fiber fed. All insoluble fiber diets and the guar gum and psyllium diets resulted in significantly higher daily fecal mass and, in general, resulted in significant dilution of total fecal steroids. With the insoluble fibers, there was a general dilution of fecal neutral steroids, which was not apparent with the soluble fibers or cholestyramine. In addition, except for the pectin- and mixed fiber-containing diets, there was reduced bacterial conversion of the primary bile acids to secondary bile acids or metabolites.     

Effect of dietary fat on the utilization of fatty acids by myocardial tissue in the rat

Weanling rats were fed high fat diets containing 40% of energy as fat for 23 d. Diets were formulated to contain equivalent content of essential nutrients per calorie for the nonfat components. Four oil mixtures provided high dietary levels of either oleic, linoleic, linolenic or erucic acid. Effect of dietary fatty acid composition on the fatty acid composition of phosphatidylcholine, phosphatidylethanolamine and cardiolipin isolated from cardiac mitochondria was examined in conjunction with the effect of diet on the oxidative activity of cardiac mitochondria. Dietary treatments that reduced the content of C16:0 in the sn-1 and sn-2 positions of phosphatidylcholine were associated with increased content of C20:1 and C22:1 fatty acids into the sn-2 position and resulted in decreased oxidative activity of cardiac mitochondria utilizing palmitylcarnitine as a substrate for oxidation. Diets high in linoleic acid did not increase membrane phospholipid content of omega 3 fatty acids, but resulted in decreased level of C20:4 omega 6. In a subsequent perfusion experiment, hearts were removed from animals fed either high erucic or high linoleic acid diets and were perfused to examine rates of fatty acid oxidation and simultaneous synthesis of high energy phosphate compounds in cardiac muscle. Diet did not affect the levels of creatine phosphate or adenine nucleotides present in the tissue on a per-gram-wet-weight basis, but production of 14CO2 from beta-oxidation of palmitic acid was lower for animals fed the high erucic acid diet than for those fed the high linoleic acid diet. Since this diet did not alter oxidation of palmitylcarnitine in vitro and as beta-oxidation of lauric acid was not decreased in the perfused heart, we conclude that mitochondrial oxidation of fatty acid was not altered by diet and that low rates observed for palmitate oxidation are attributable to reduced palmitylcarnitine synthesis.     

Effect of dietary cholesterol and degree of fat unsaturation on plasma lipid levels, lipoprotein composition, and fecal steroid excretion in normal young adult men

Effect of four test diets differing in the ratio of polyunsaturated to saturated fats (P/S, 1.8 vs 0.28) and two cholesterol levels (1,000 vs 300 mg/day) for each level of the P/S ratio was determined on plasma lipid levels, lipoprotein compositions and concentrations, and fecal steroid excretion in a controlled diet study with 11 normal young men using a crossover design. Plasma cholesterol levels were significantly decreased by the diets high in P/S ratio regardless of the dietary cholesterol levels (14% decrease by high cholesterol and 20% in low cholesterol) while the diets low in P/S ratio increased cholesterol by an average of 24 and 22% in presence of high and low cholesterol, respectively. Lipids and apoproteins of lower-density lipoproteins were changed in accordance with those of plasma cholesterol but changes in high-density lipoprotein (HDL) appear to depend on both cholesterol content and P/S ratio. Dietary cholesterol level profoundly influenced the excretion of neutral sterols and diets high in P/S ratio significantly (p less than 0.05) increased fecal bile acid extraction. The present study demonstrated that dietary polyunsaturated fats, when a moderate amount was consumed, were effective and beneficial hypocholesterolemic nutrients without reducing HDL-cholesterol.