Jon A. Story

Experimental atherosclerosis in rabbits fed cholesterol-free diets. Part 7. Interaction of animal or vegetable protein with fiber.

Rabbits were maintained for 10 months on a semipurified, cholesterol-free atherogenic regimen. All diets contained sucrose (40%) and hydrogenated coconut oil (14%). The protein (25%) was either casein or soya protein and the fiber (15%) was either wheat straw, alfalfa, or cellulose. Within either protein group the order for induction of cholesteremia was cellulose=wheat straw greater than alfalfa. For atherogenesis, the effect was cellulose greater than wheat straw greater than alfalfa Soya-wheat straw or soya-cellulose diets were less cholesteremic and atherogenic than their casein counterparts. When alfalfa was the fiber, the two types of protein were almost equivalent. Our results show that casein may be more cholesteremic and atherogenic than soya protein under certain conditions (cellulose or wheat straw as fiber) but the addition of alfalfa to the diet renders the two proteins equivalent.

Experimental atherosclerosis in rabbits fed cholesterol-free diets: 5. Comparison of Peanut, Corn, Butter, and Coconut Oils

Abstract Four groups of Dutch belted rabbits were fed a semipurified diet containing 40% sucrose, 25% casein, and 14% fat for 10 months (without added cholesterol). The fats were peanut oil (PNO), corn oil (CO), butter oil (BO), and coconut oil (CNO). All diets were hyperlipidemic and hyperlipoproteinemic. The highest serum cholesterol and triglyceride levels were observed in the CNO groups, 330 and 286 mgm/dl, respectively. Serum cholesterol and triglyceride levels in the other groups (mgm/dl) were: PNO-205 and 51; CO-152 and 28; BO-292 and 48. The serum of α β lipoprotein cholesterol ratios were: PNO-0.28; CO-0.28; BO-0.19, and CNO-0.13. This ratio is about 0.35–0.40 in normal Dutch belted rabbits. Liver cholesterol levels were similar in all groups (1.35 ± 0.5 gm/100 gm). Liver triglyceride levels were (gm/100 gm): PNO-0.37; CO-0.55; BO-0.66; CNO-0.39. The most severe gross atherosclerosis was observed in the CNO group (25% of surface area) and the least in the CO group (2%). The involved surface area in the other two groups was: PNO-10% and BO-14%. Microscopic evaluation of the severity of the aortic lesions indicated that the rabbits fed CNO, BO, and PNO had the most frequent and severe lesions. In contrast, the animals fed CO consistently showed much less aortic disease. Gross aortic examination revealed distinct differences in the characteristics of atherosclerotic lesions induced by the four dietary fats. The most extensive lesions, observed in rabbits fed CNO, were characterized by intimal proliferation spread over the area of lipid deposition. BO tended to produce aortic lesions rich in lipid but a relatively small number of cells and little collagen deposition. The aortic lesions in rabbits fed PNO contained relatively little lipid and were characterized by thick fibrous plaques due to prominent intimal proliferation and a high proportion of collagen. The rabbits fed CO developed few aortic lesions, with minimal intimal proliferation and very little lipid. The relative atherogenicity of PNO was an unexpected finding.

Age-related changes in the lipid metabolism of Fisher 344 rats

Lipid metabolism of male Fisher 344 rats aged 2–24 months was studied. Serum and liver cholesterol levels did not display the age-related gradual increase seen in other rat strains. An increase in the serum plus liver cholesterol pool from 2 to 6 months was followed by a plateau through 18 months and then another increase at 24 months of age. The triglyceride pool increased from 2 to 6 months and then remained unchanged through 24 months of age. Cholesterol synthesis from acetate decreased 50% between 2 and 9 months and fell only slightly through 24 months of age. Assay of 3-hydroxy-3-methyl glutaryl Coenzyme A (HMG-CoA) reductase showed a similar pattern but did not decrease further after 9 months of age. Cholesterol 7α hydroxylase activity was not significantly altered by age. These age- and strain-related differences present an opportunity for a comparative study of the aging process using the parameters of lipid metabolism as indicators.

Experimental atherosclerosis in rabbits fed cholesterol-free diets Part 9. Beef protein and textured vegetable protein

Rabbits were fed a semipurified diet containing 40% sucrose, 25% protein, 15% fiber and 14% tallow. The proteins fed were beef (B), textured vegetable protein (TVP) and casein (C). One diet contained beef-TVP (1 : 1) and in another a soy carbohydrate fraction, spent flakes, was added to the diet; it provided 2.2% protein and 10.5% fiber. TVP provided 6.4% soluble carbohydrate and 10.5% fiber. The diets were fed from 8 months. Diets containing beef protein or casein gave significantly higher serum cholesterol levels and atherosclerosis and significantly lower serum HDL-cholesterol than did the other 3 diets. The beef-TVP (1 : 1) diet gave low serum cholesterol (67% below beef) levels and atherosclerosis (47% below beef). This effect is probably due to the protein. The diet containing spent flakes gave low serum cholesterol levels (44% below beef) and atherosclerosis (45% below beef). This effect is attributed to the different fiber. The lowest serum cholesterol levels and least severe atherosclerosis were observed in the rabbits fed TVP.

Experimental atherosclerosis in rabbits fed cholesterol-free diets: 4. Investigation into the source of cholesteremia☆

Abstract The metabolism of exogenous and endogenous cholesterol was studied in rabbits fed a normal diet of rabbit chow or an atherogenic, semisynthetic diet ( SS ) containing 40% carbohydrate, 25% casein, and 14% hydrogenated coconut oil. The SS diet was more cholesteremic, betalipoproteinemic and atherogenic. More cholesterol was absorbed and more synthesized by rabbits on the SS diet and more radioactive cholesterol was recovered from their lesions. The chow-fed rabbits excreted 4 times as much feces over a 3 day period. Biliary cholesterol and total bile acids were 2.2 and 2.6 times higher in the SS group. The biliary cholesterol-specific activity was significantly higher in the SS group but cholanoic acid-specific activities and primary/secondary bile acid ratios were significantly lower. The data suggest that one reason for the cholesteremic effect of the SS diet is a reduced level of degradation of endogenous cholesterol to bile acids.

Bile acid metabolism and fiber

Studies in experimental animals and in humans have shown a definite interaction of dietary fiber with bile acid metabolism. In experimental animals, some types of fiber have been shown to increase bile acid excretion as well as increase pool size and turnover of bile acids. In man, increases in bile acid excretion have been observed but not consistently. Alternations in excretion and biliary bile acid levels indicate an influence of dietary fiber in bile acid metabolism. In vitro experiments have attempted to determine the nature of the fiber-bile acid interaction. Some types of fiber and some components of fiber have been shown to bind bile acids and bile salts in appreciable quantities. The capacity for various types of fiber to bind bile acids or bile salts is quite variable, and a high capacity seems to correspond with a hypocholesteremic effect. A great deal of research is still needed for elucidation of these interactions of fiber and bile acid metabolism and the resultant beneficial effects on cholesterol metabolism and the disease-related abnormalities in cholesterol metabolism.

Soluble Corn Fiber Increases Calcium Absorption Associated with Shifts in the Gut Microbiome: A Randomized Dose-Response Trial in Free-Living Pubertal Females

BACKGROUND Soluble corn fiber (SCF; 12 g fiber/d) is shown to increase calcium absorption efficiency, associated with shifts in the gut microbiota in adolescent males and females who participated in a controlled feeding study. OBJECTIVE We evaluated the dose response of 0, 10, and 20 g fiber/d delivered by PROMITOR SCF 85 (85% fiber) on calcium absorption, biochemical bone properties, and the fecal microbiome in free-living adolescents. METHODS Healthy adolescent females (n = 28; aged 11-14 y) randomly assigned into a 3-phase, double-blind, crossover study consumed SCF for 4 wk at each dose (0, 10, and 20 g fiber/d from SCF) alongside their habitual diet and were followed by 3-d clinical visits and 3-wk washout periods. Stable isotope ((44)Ca and (43)Ca) enrichment in pooled urine was measured by inductively coupled plasma mass spectrometry. Fecal microbial community composition was assessed by high-throughput sequencing (Illumina) of polymerase chain reaction-amplified 16S rRNA genes. Mixed model ANOVA and Friedman analysis were used to determine effects of SCF on calcium absorption and to compare mean microbial proportions, respectively. RESULTS Calcium absorption increased significantly with 10 (13.3% ± 5.3%; P = 0.042) and 20 g fiber/d (12.9% ± 3.6%; P = 0.026) from SCF relative to control. Significant differences in fecal microbial community diversity were found after consuming SCF (operational taxonomic unit measures of 601.4 ± 83.5, 634.5 ± 83.8, and 649.6 ± 75.5 for 0, 10, and 20 g fiber/d, respectively; P < 0.05). Proportions of the genus Parabacteroides significantly increased with SCF dose (1.1% ± 0.8%, 2.1% ± 1.6%, and 3.0% ± 2.0% for 0, 10, and 20 g fiber/d from SCF, respectively; P < 0.05). Increases in calcium absorption positively correlated with increases in Clostridium (r = 0.44, P = 0.023) and unclassified Clostridiaceae (r = 0.40, P = 0.040). CONCLUSIONS SCF, a nondigestible carbohydrate, increased calcium absorption in free-living adolescent females. Two groups of bacteria may be involved, one directly fermenting SCF and the second fermenting SCF metabolites further, thereby promoting increased calcium absorption. This trial was registered at clinicaltrials.gov as NCT01660503.

Cholesterol vehicle in experimental atherosclerosis. Part 16. Effect of peanut oil on pre-established lesions.

Rabbits were fed an atherogenic diet (2% cholesterol and 6% corn oil) for 8 weeks and then divided into groups of equal average serum cholesterol levels. One group was autopsied, and the others were returned to cholesterol-free diets consisting of commercial laboratory ration or ration augmented with 6% corn oil, peanut oil or PGF, a fat designed to resemble peanut oil minus arachidic and behenic acids. The animals were maintained on the diets for 8 more weeks. On all regimens, severity of atherosclerosis was exacerbated. The extent of exacerbation was significantly less in rabbits fed corn oil than in the others. The extent of exacerbation of lesions appears to be a function of the level of unsaturation of the dietary fats.

Fiber, hypercholesteremia, and atherosclerosis

Epidemiological data suggest that populations subsisting on high fiber diets are free of a number of the diseases of Western civilization, among them coronary heart disease. Studies in animals and man show that each type of fiber exerts it own specific influence. Thus, in man bran has no effect on serum lipids, but pectin lowers cholesterol levels. In animals fed atherogenic diets, alfalfa and pectin exert some measure of protection, but cellulose does not. To fully understand the mode of action of dietary fiber, it is necessary to ascertain the mechanism(s) of action of each chemical component of that fiber.

Age-strain interrelations in lipid metabolism of rats

Various aspects of lipid metabolism were compared in Fisher 344 (F) and Sprague-Dawley (SD) rats aged 2, 6, 12, 18 and 24 months. The analyses included free and total cholesterol of serum and liver, LCAT, hepatic HMG-CoA reductase, cholesterol 7α-hydroxylase, fatty acid synthetase, acetyl CoA carboxylase and cholesterol synthesis from acetate or mevalonate. The body weight of SD rats increases with age whereas that of F rats plateaus at 9–12 months. Liver and aorta cholesterol levels were comparable for the 2 strains. Serum cholesterol varied but was usually lower in F rats. HMG-CoA reductase and cholesterol 7α-hydroxylase activities were not significantly different. Cholesterol synthesis from acetate was significantly higher only in 2-month-old F rats; synthesis from mevalonate was similar at each level. Acetyl CoA carboxylase and fatty acid synthetase activity were generally higher in F rats at every age level. The major difference between F and SD rats is in their pattern of weight gain with age. Differences in lipid metabolism are most marked between the young (2-month) rats.