Cholesterol-free diet

Bises, and D. M. Klurfeld. Experimental atherosclerosis in rabbits fed cholesterol-free diets. Atherosclerosis 1982 41(2-3) 279-284-... 

In studying results from both chickens and man, Fisher et al. (67) concluded that pectin has a hypocholesterolemic effect only when fed with dietary cholesterol. On cholesterol-free diets, plasma cholesterol is not affected by dietary pectin. Subjects fed pectin with a cholesterol-containing diet had plasma cholesterol levels that were lower relative to those of subjects on the cholesterol control diet, but not relative to those of subjects on a cholesterol-free control diet. 

Impairment of bile acid absorption and consequent loss of these acids via excretion presumably causes an increase in hepatic conversion of cholesterol to bile acids. This conversion lowers serum cholesterol, particularly when serum contains high levels of cholesterol derived from dietary intake. However, when fed with a cholesterol-free diet, 10% pectin supplementation stimulated a 3-fold increase in cholesterol biosynthesis (77). Biosynthesis of phospholipids and triglycerides also increased significantly hence, it was suggested that these increases occurred in response to diminished fat absorption occasioned by pectin intake. This compensatory biosynthesis of cholesterol and lipids may account for pectin s inability (in most cases) to lower serum cholesterol levels in animals fed cholesterol-free diets. 

Table I. Effect of Pectin on Rats Fed a Cholesterol-Free Diet (54).

Studies of Kritchevsky et al. (1989) on experimental atherosclerosis in rabbits fed cholesterol-free diets revealed a greater influence of animal protein and of partially hydrogenated soybean oil on development of atherosclerosis than plant protein and unsaturated soybean oil. 

The mechanism of the inhibition of the HMG-CoA reductase by bile adds shown in Fig. 14 is a matter of controversy. Weis and Dietschy did not observe any influence of taurocholate on cholesterol synthesis in bile fistula rats fed a cholesterol-free diet, and concluded that the inhibitory effect of bile acids on cholesterol synthesis may be related to the increased absorption of cholesterol by the presence of bile acids in the intestine [247]. However, Hamprecht et al. were able to demonstrate a reduction of HMG-CoA reductase activity in lymph fistula rats infused with cholate [248]. Results by Shefer et al. also indicate that bile acids inhibit HMG-CoA reductase directly [212]. It seems likely that the inhibitory effect of the bile acids on HMG-CoA reductase may involve both direct and indirect effects. It was recently established that the stimulation of HMG-CoA reductase activity in response to treatment with cholestyramine is associated with an increase of the specific mRNA [258]. 

Oat bran did not change plasma cholesterol levels. Others (25) have shown that oat bran decreases total plasma cholesterol and increases HDL in cholesterol fed rats. The effect seems to be related to soluble oat gums. The lack of effect of oat bran in our experiment might be due to the fact that we studied this fiber only in cholesterol-free diets. Soluble gums may also have been lost in preparing this fiber enriched oat bran (81% dietary fiber). 

Fecal Steroid Excretion of Rats at 4th Day Refeeding Period on Cholesterol-Free Diet... 

Similar data have been reported for liver cholesterol levels in rats (7). Germfree and conventional rats fed a cholesterol-free diet had similar liver cholesterol levels however, as the amount of cholesterol in the diet was increased, the liver cholesterol levels of the germfree rats rose three times higher than did those of the comparable conventional rats. In these rats, the serum cholesterol levels did not change with microbiological status or dietary cholesterol. 

Large changes in serum cholesterol levels have been shown to occur when gnotobiotic swine were fed a cholesterol-containing diet. Gnotobiotic swine fed a cholesterol-containing diet had serum cholesterol levels of about 1000 mg %, but when they were removed from isolators and raised in a nonsterile environment, the serum cholesterol levels fell to 100 mg % within 3 weeks (8). The fall in serum cholesterol could be correlated with the development of an intestinal microflora which metabolized the primary bile acids to secondary bile acids. Similar swine fed an identical but cholesterol-free diet had serum cholesterol levels of about 100 mg % during both periods. 

During the course of a study of the effects of polyunsaturated fatty acid derivatives on cholesterol metabolism, Nakatani and his associates [432] found that amides of linoleic acid showed a pronounced cholesterol-lowering effect in mice, rats, and rabbits which had been fed cholesterol. However, addition of these amides to a cholesterol-free diet did not show any significant effect on cholesterol levels. Metabohc studies have suggested that iV-cyclohexyl linoleamide (CXCI) interferes with the absorption of cholesterol from the intestine. The antiatherosclerotic effect of compound CXCI has also been studied by Kritchevsky and Tepper [433]. They have found that the administration of 600-900 mg/day of CXCI to rabbits maintained on an atherogenic dief led to reduced atheromata however, it was found to be ineffective at a dose of300mg/day. This lower dose has been found to reduce serum and hver cholesterol levels [433]. 

The regulatory implication of such a proposal is shown in Fig. 9. In the event of cholesterol excess, such as dietary cholesterol entering the cell, the regulatory adjustment would be as follows HMG-CoA reductase activity would decline, as a consequence of phosphorylation, whereas the activities of AC AT and 7 a-hydroxylase enzymes would be stimulated. In the instance of cholesterol deprivation, for example a cholesterol-free diet or a cultured liver cell grown in lipid-deficient medium, the regulatory adjustment would be HMG-CoA reductase activity would increase as a consequence of dephosphorylation, but AC AT and 7a-hydroxylase activities would decline under these conditions. 

Factors affecting atherosclerosis in rabbits fed cholesterol free diet. 

The serum lipids in men receiving high cholesterol and free cholesterol-free diets. 

Another peculiar effect of cis-9, trans- CLA isomer is its antiatherogenic effects in different experimental models. Probably the most striking is its effect on rabbits, the best experimental model for atherogenesis. In this model, cis-9, trans- CLA in the diet decreased atherogenesis by 50% when fed as a component of a semi-.purified diet containing 0.2% cholesterol and reduced established lesions by 26% when fed as part of a cholesterol-free diet (Kritchevsky et al., 2004). Cancer and atherosclerosis have some common features among them such as sustained cell proliferation and inflammation. It is likely that cis-9, trans- CLA affects both by increasing apoptosis (Ip et al.,... 

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