Relation of types of dietary fat to cardiovascular damage in mice

Nine edible oils or fats (hydrogenated coconut, cod liver, Wesson, linseed, olive, butter, lard, corn and cocoa-butter) were fed for 50–90 days to study the relation of saturation, chain length and essential fatty acid content to production of cardiovascular lesions. The specific oil or fat (selected for ranges in the above variables) was used as the dietary lipid in a high-fat (28%), low-protein (8%), hypolipotropic diet. Half of the animals received identical diets containing choline chloride (2 gm/100 gm of diet) as a lipotropic supplement. Atrial mural thrombosis and ventricular myocardial necrosis and calcification developed in all dietary groups. Atrial thrombosis was the most frequent lesion. The greatest incidence of atrial thrombosis occurred in mice fed the choline-deficient, butter-containing diet (92%) and the lowest incidence with the supplemented cod liver oil diet (20%). The diet containing unsupplemented hydrogenated coconut oil produced the greatest incidence of ventricular necrosis (79%) and that with choline-supplemented cocoa-butter the lowest (8%). Ventricular calcification was most extensive within the unsupplemented cod liver oil group (83%), most limited in the supplemented lard group (5%). In general, choline-supplemented diets produced a lower incidence of cardiac damage. Little correlation existed between the composition and characteristics of specific fats and their activity in producing the specific cardiac lesions observed here.     

Preference for high carbohydrate over various high fat diets by diabetic rats

Streptozotocin-diabetic male rats were hyperphagic relative to nondiabetic controls when offered only high carbohydrate (CHO) laboratory chow. Diabetics and controls ate about the same amount of high fat diets made from 67% w/w chow and 33% either coconut oil (saturated) or safflower oil (unsaturated). However, when offered a simultaneous choice of high fat diets and chow, nondiabetics and low dose (35 mg/kg) streptozotocin-diabetics showed a preference for the high fat diet: in contrast the high dose (65 mg/kg) streptozotocin diabetics developed a preference for chow. When pairs of isocaloric synthetic diets were offered, diabetics again preferred low fat/high CHO to high fat/low CHO diets, but the actual intake of fat was not constant across different diet pairs. Nondiabetics also selected away from the high fat diets in these synthetic diet pairs, even when saccharin was added to the high fat diet in an attempt to equate its sweetness with that of the paired low fat-high CHO diet. Plasma ketone levels of diabetics during obligatory high fat diet consumption were negatively correlated with their subsequent preference for the fat diet over simultaneously-offered chow. These data show that strong dietary preferences do not develop for fat in diabetics and suggest that high fat diets do not have net beneficial postingestional effects in these rats.     

Protein selection, food intake, and body composition in response to the amount of dietary protein

Though not universally observed, moderately low-protein diets have been found to increase caloric intake and body fat. It appears that animals overeat in calories in order to obtain more dietary protein. For animals to control protein intake, they must be able to distinguish between two isocaloric diets containing different percentages of protein and make the appropriate dietary selection on the basis of their previous history of protein intake. Experiment 1 examined the 24-h diet selection (5 vs. 35% casein) of Sprague-Dawley rats that had been previously fed diets containing various percentages of dietary protein (5, 10, 20, 35, or 60% casein). Animals fed 5, 10, or 20% dietary protein showed a preference for the higher protein selection diet. In contrast, no significant diet preference was found in animals pre-fed the two higher levels of dietary protein (35 or 60% casein). In this study, daily food intake and body fat of rats fed the low-protein diets (5 and 10% casein) were similar to rats fed the 20% casein diet. Experiment 2 examined the effects of the level of methionine supplementation on rats fed 10% casein. In this study, food intake and body fat were increased by approximately 20% in rats fed 10% casein diets, regardless of the level of methionine supplementation (0.3 vs. 0.15%). Together, the results suggest that the presence of low-protein-induced hyperphagia helps maintain body protein levels in the face of moderately low dietary protein and promotes an increase in the amount of body fat and energy.     

Dietary fat-induced hyperphagia in rats as a function of fat type and physical form

The influence of dietary fat on food intake and weight gain was assessed by feeding adult female rats diets that differed in the type and form of fat, as well as in the availability of other macro- and micronutrients. Compared to chow-fed controls, the various fat diets increased total food intake by 4% to 27%. Specifically, rats fed chow and a separate source of fat (fat option diet) consumed more fat and total calories, and gained more weight when the fat source was emulsified corn oil rather than pure corn oil or was vegetable shortening rather than corn oil. However, corn oil and shortening had similar effects on caloric intake and weight gain when presented as emulsified gels. Also, pure and emulsified-gel forms of shortening did not differ in their effects on caloric intake and weight gain. Supplementing the vegetable shortening with micronutrients, however, enhanced its hyperphagia-promoting effect. The results of two-choice tests revealed that the rats' preferences for the orosensory properties of the various fat sources did not account for the differential hyperphagias obtained. Rather, it appears that long-term fat selection and caloric intake are influenced primarily by postingestive factors. Fat selection and total intake were determined not only by the fat source itself, but also by the other diet options. That is, rats selected more fat and consumed more calories when chow was the alternative food than when separate sources of carbohydrate and protein were available.     

Body weight and longevity in genetically obese and non-obese mice fed fat-modified diets

Polygenically obese and genetically related non-obese male mice were fed ad libitum purified diets differing in quantity or type of fat from weaning onward to determine effects upon weight gain and life span. Non-obese mice lived 71% longer than mice in the obese line (mean = 753 d versus 441 d). Obese mice fed a low-fat diet containing 1% corn oil by weight lived 26% longer than their obese counterparts fed high fat diets containing 20% additional fat as either corn oil or beef tallow. The low fat diet had more of a normalizing effect upon longevity than upon body weight in polygenically obese mice. Conversely, dietary fat concentration had little effect upon longevity in non-obese mice and more effect upon body weight than in genetically obese mice. Type of dietary fat had little effect upon body weight and no effect upon longevity. The results of this study suggest that life span was only partially explained by body weight, and furthermore, that genetics play a greater role than body weight or dietary fat concentration in determining life span.     

Morphologic effects of dietary plant and animal lipids rich in docosenoic acids on heart and skeletal muscle of cynomolgus monkeys.

Cynomolgi (Macaca fascicularis) were fed diets containing 25% rapeseed oil (RSO), partially hydrogenated herring oil (PHHO), or a 3:1 mixture of lard and corn oil as control for 4 months. The RSO contained approximately 25% of the fatty acids as erucic acid; the PHHO contained a similar concentration of mainly cetoleic acid. The control diet did not include such fatty acids. At the time of necropsy, the RSO- and PHHO-fed monkeys showed myocardial and skeletal muscle lipidosis. Foci of mononuclear cell infiltration, although infrequent, occurred in all three groups and were thought to be nonspecific. The only significant intergroup difference in serum biochemical or hematologic parameters was an increase in serum glutamic-oxaloacetic transaminase activity in both RSO and PHHO groups. Ultrastructural studies confirmed the presence of lipidosis in cardiac and skeletal muscle and revealed mild mitochondrial degeneration, causing a depression of the P/O ratio of the RSO group and a State III respiratory rate depression of the PHHO group. The difference in the exposure/life span ratio represented by this experiment may account for the absence of clear intergroup differences such as are reported in rats used in similar studies, but a true species difference in regard to dietary oils containing docosenoic acids has to be considered as well.     

The effect of dietary fat on malondialdehyde concentrations in Fischer 344 rats

The effects of dietary fat and age on the level of malondialdehyde (MDA), a product of lipid peroxidation, were investigated in cerebellum, kidney, and liver tissues of female Fischer 344 rats. Groups of rats were fed diets containing various levels of corn oil (3, 5, 10, 15, or 20%), starting at 57 days of age, for a duration of 2, 10, or 20 weeks. High fat diets are thought to promote tumor formation, diabetes, and cardiovascular diseases via induction of oxidation stress, and this can begin early in the lifespan. However, it was observed that rats chronically consuming 3 and 5% corn oil diets yielded significantly higher levels of MDA, as analyzed by high-performance liquid chromatography, compared with those fed higher fat diets. After 20 weeks of feeding, the concentration of MDA in each of the three organs studied showed no significant differences among rats consuming diets containing 10, 15, or 20% corn oil. The levels of MDA were highest in the cerebellum, followed by kidney, and lowest in liver. Over the 20-week feeding period, a decrease in MDA level in both cerebellum and liver was observed.     

Cholesterol-induced alteration in liver mineral concentrations in corn oil and olive oil fed rats.

This study was undertaken to compare the effects of 1% cholesterol (Ch) on some liver mineral concentrations in rats fed with corn oil (C) or olive oil (O). Male Sprague-Dawley rats (n = 4 per group) were fed AIN76A semi-purified diets containing either 5% corn oil or 5% olive oil replacing corn oil with or without 1% cholesterol for 21 days. The analysis of minerals: Phosphorous (P), Potassium (K), Magnesium (Mg), and Sulfur (S), of liver were conducted by inductively coupled plasma (ICP) spectroscopic method. In the C fed rats addition of 1% cholesterol produced significant increase in P concentrations but not K, Mg, and S concentrations. In contrast, in O fed rats, 1% Ch significantly decreased Mg and S concentrations. There was no significant change in K and P concentrations. In conclusion, this study describes the interactions between dietary oils and cholesterol on certain mineral concentrations in liver of rats. The results obtained may have clinical significance and nutritional significance in cardiovascular health.     

Influence of dietary lipid upon ultraviolet light-carcinogenesis

Dietary fats are known to influence the rate of formation of certain types of chemically-induced and spontaneous tumors. An earlier report indicated dietary fat also plays an important role in predisposition to ultraviolet light (UV)-carcinogenesis. Thus, an examination of the effects of dietary lipid level, degree of saturation, and antioxidant supplements on UV-carcinogenesis was undertaken. Twelve groups of 42 animals each received a restricted, semipurified, isocaloric diet containing 4%, 12%, or 12% (60% hydrogenated) corn oil with or without antioxidants (2%, w/w). A regimen of escalating UV irradiation was employed until an accumulative dose of 142 J/cm2 had been delivered. Animals were evaluated weekly for actinic lesions and biweekly for body weights, hematocrits, and serum triglyceride levels. A cumulative distribution function of time to tumor formation was estimated for all irradiated groups from which tumor development time in 50% (TDT50) of the population was derived. Although there were no significant differences in TDT50's between animals receiving low and high unsaturated lipid dietary regimens, animals receiving hydrogenated corn oil demonstrated a significantly (P less than 0.01) greater TDT50. Further, animals receiving hydrogenated 12% corn oil demonstrated fewer tumors per animal than those receiving either level of unsaturated corn oil. Antioxidants had no effect on TDT50's within any of the dietary groups. However, in regard to number of tumors per animal, greater tumor multiplicity was observed in groups receiving unsaturated lipid and antioxidants. These data demonstrate that the degree of dietary lipid saturation modifies the carcinogenic response to UV and, in conjunction with an earlier report, suggest that dietary lipid may modify the previously reported inhibitory effect of antioxidants on UV carcinogenesis. It may be concluded that adherence to dietary standards is as important as other experimental parameters when comparisons of UV effects are involved.     

Modulation of DNA modification (I-compound) levels in rat liver and kidney by dietary carbohydrate,protein, fat,vitamin, and mineral content

I-compounds are DNA modifications detected by ³²P-postlabeling that increase with age in rodents without known carcinogen exposure. Diet type (natural ingredient versus purified) greatly influences patterns and levels of I-compounds. To test the hypothesis that I-compound formation is affected, also, by dietary macro- and micronutrients, effects of carbohydrate, protein, fat, vitamin, and mineral content on rat liver and kidney I-compounds were determined. Female Sprague-Dawley rats were fed basic or modified AIN-76A purified diets for 3–6 months. High protein (HP) diet (50%, w/w) increased I-compound levels in liver but not kidney. High carbohydrate (HC) diet (78%) produced a significant increase in the polar as well as total I-compound levels in both tissues. High fat diets (20%) elicited significantly lower levels of liver I-compounds than HC, HP, and basic diets. There were few significant differences between high polyunsaturated (safflower oil) and saturated fat (lard) diet groups. No qualitative differences in I-compound profiles were observed in either tissue. In rats fed basic diet supplemented with vitamins and/or minerals, increased vitamin content reduced the levels of polar I-compounds in liver. No extra diet-induced adducts were observed; all effects were of a quantitative nature. These data provide direct evidence that nutrients significantly influence I-compound levels and support the hypothesis that normal metabolism of nutrients leads to the production of small amounts of DNA-reactive electrophiles. These observations suggest a novel mechanism where nutrient composition of the diet may play a role in development of neoplasia and other adverse health effects.     

Rainbow trout can discriminate between feeds with different oil sources

The purpose of present two-choice trials was to examine the capacity of groups of juvenile rainbow trout to differentiate between two isolipidic diets containing distinct oils and to detect an eventual preference. The choice was offered by means of two self-feeders per tank. One feeder distributed a standard diet with fish oil (FO), the other a diet containing vegetable oil, either rich in linolenic acid (linseed oil, LO), linoleic acid (sunflower oil, SO), or oleic acid (rapeseed oil, RO). Each 15-day preference test was preceded by a 15-day adaptation period during which both feeders distributed the same diet. The tests were followed by a 10- to 15-day validation period in order to confirm that feeder solicitations were steered by the characteristics of the diets. Preferences were expressed as relative changes in feed demands for a specific feeder. Averaged over all groups, the preference tests demonstrated the capacity of rainbow trout to discriminate between a diet with FO and a diet containing vegetable oil, and indicated a general preference for the diet with FO over the other diets irrespective of whether they received the diet with fish oil (Experiment 1) or with vegetable oil (Experiment 2) prior to the preference test. The tests also indicated a difference in the extent of relative avoidance of each of the three vegetable oil diets. Diet LO was the most avoided, as indicated by the 37-39% decrease in demands for the feeder with diet LO (P<0.05). Diet RO was the best accepted, causing a decrease in feed demands of only 15-17% (P>0.05). The avoidance of diet SO at the end of the preference test was 30% (P>0.05) after an initially higher avoidance of 43% (P<0.05). It is believed that the metabolic consequences of the excess of linolenic or linoleic acid negatively affected the feed acceptances of diets LO and SO. Further work is needed to elucidate a possible interference of differences in palatability. In all groups, the lower demands for the vegetable oil diets were compensated by increased demands for diet FO. Hence, changes in diet selection had no effect on total feed or energy intakes, measured as the sum of both selections.     

Aversion of the cat to dietary medium-chain triglycerides and caprylic acid

Young, specific-pathogen-free cats were fed purified diets containing different sources of fat. Food intake was depressed and cats lost weight when the diet contained either hydrogenated coconut oil (HCO) or medium-chain triglycerides (MCT). With an MCT preparation enriched in 8:0 (MCT8), cats would not eat after first tasting the diet. When cats were offered a choice of two high-fat diets, they chose the basal diet over a diet containing 30% HCO, by a ratio of 4.5:1. Low levels of MCT8 (5% or 10% by weight) were also rejected, whereas cats did not reject 5% or 15% MCT12. Caprylic acid, at 0.1-1.0% of the diet, was rejected. In other studies, food intake and body weight decreased when HCO was added to a fat-free diet. Cats fed 25% or 35% HCO lost weight. When 5% safflower seed oil was added to the HCO diets, body weights and food intake improved, but were still less than optimal. These studies indicate that the food intake depression in cats fed dietary HCO and MCT is primarily a result of impalatability, and that the fatty acid moiety may be responsible for the aversion.     

Role of dietary corn oil in the function of hepatic drug and carcinogen metabolizing enzymes of starved-refed rats: response to the mixed function oxidase inducer, 3-methylcholanthrene

Hepatic microsomes from rats starved 48 hours and refed diets containing zero, 3 or 20% corn oil metabolized benzo(a)pyrene, aniline and N-nitrosodimethylamine in proportion to the quantity of corn oil in the diet. No diet-related changes in apparent Km for these reactions were evident. The content of microsomal cytochrome P-450 was also clearly dependent upon the content of corn oil in the refed diets. When metabolism of these three substrates is expressed as product formed per unit of cytochrome P-450, the activities are least in microsomes from rats fed the 20% corn oil diet, suggesting that P-450 species responsible for metabolizing substrates other than these are enhanced preferentially. Cytosolic glutathione S-transferase activities are also increased with increasing corn oil in the diet. The administration of 3-MC increased cytochrome P-448 content of microsomes from all rats, regardless of diet, however highest content was present in microsomes from rats fed the 20% corn oil diet. Induction of benzo(a)pyrene hydroxylase was not influenced by dietary corn oil and, as anticipated, 3-MC caused significant repression of DMN N-demethylase in microsomes from rats fed the 20% corn oil diet. In like manner, 3-MC induced glutathione S-transferase only in cytosol from rats fed the fat-free diet.     

Mutagenicity of high fat diets in the colon and small intestine of transgenic mice

Dietary fat has been implicated as a cause of colon cancer byepidemiological studies. Unfortunately, these studies are compatiblewith high fat as either initiator or promoter. Since initiatorsare normally mutagenic, we have tested the mutagenicity of highfat diets in the intestinal epithelium at two loci. The Dlb-Iassay, used in the small intestine, detects a wide spectrumof mutations. The lacI assay (Big Blue^TM Mouse assay) is notas sensitive to some types of mutation as is Dlb-I but was usedin the colonic epithelium. Mice suitable for both assays werefed isocaloric high fat diets and subsequently assayed for somaticmutation. The diets consisted of: (i) a mixture of beef tallow,butter and lard totalling to 31% w/w of the diet (AIN-76A) upto 17 weeks; and (ii) corn oil, beef tallow, lard or butterindividually, at 31% w/w of the diet for 5 and 9 weeks. Thesediets provided 50% of the calories from fat. The weights ofthe experimental and control mice were similar throughout theexperiment. No significant increases in mutant frequencies wereobserved on any high fat diet compared to controls, so we concludethat uncooked fats are not mutagenic and are not initiatorsof carcinogenesis in the intestinal epithelium. ¹To whom correspondence should be addressed     

Some effects of a grain-based mash diet on cholesterol metabolism in swine

The aim of the first part of this study was to find out in swine how much fat could be included in a cholesterol-free semi-purified diet without resulting in changes in serum cholesterol levels or hepatic microsomal HMG-CoA reductase activities from those in swine fed a grain-based mash diet. Graded levels of peanut oil from 5 to 40% by calories were included in a casein-carbohydrate-cellulose based diet and effects compared with those in swine fed mash (10% fat) for 2 weeks. Serum cholesterol levels were essentially unaffected by any of the diets. However, in the semipurified diet-fed swine at all levels of dietary fat hepatic microsomal HMG-CoA reductase activities were reduced to values circa 25% of those in the mash-fed swine. This is as great as the reduction from mash levels of activity produced by high fat, high-cholesterol hyperlipidemic diets.The aim of the second part of the study was to find out in terms of whole body cholesterol balance difference in the effects of a cholesterol-free, low-fat (9%) semi-purified diet and a mash diet that might account for the differences in hepatic microsomal HMG-CoA reductase activities. The principal difference proved to be in the fecal output of bile acids (908 ± 86 mg/day on mash vs 292 ± 11 mg/day on a low-fat semi-purified diet). Thus the higher hepatic microsomal HMG-CoA reductase activities in the mash fed swine are presumably in response to the greater loss of steroids. The mixed natural fibers in the grain-based mash diet, as compared to cellulose only in the other, probably accounts for the increased fecal output of bile acids.     

Effect of exercise on Hepatic cholesterof of rats fed diets high in saturated or unsaturated fats

Summary Rats have been fed diets containing 24.2% coconut or corn oil or an equal mixture of each for 14–18 weeks. Half of the animals in each dietary group were exercised by running in motor-driven work wheels throughout the entire experimental period. During the final 10–14 weeks, these exercised animals ran continuously for 60 min at 1.0 mph or faster each day. Comparisons between sedentary groups revealed that hepatic cholesterol and excretion of digitonin precipitated sterols in the feces increased (P < 0.01) as the per cent of unsaturated fat (corn oil) in the ingested food increased. In contrast, total liver lipid decreased (P < 0.01) as the consumption of corn oil increased. No change in plasma cholesterol occurred in the sedentary rats in response to the three diets. Hepatic cholesterol of the exercised groups was significantly less (P < 0.05–P < 0.01) than that of their respective control groups (same diet). However, the group fed the corn oil diet had a significantly higher (P < 0.01) liver cholesterol after exercise than did the exercised group fed the coconut oil diet. Liver lipid was reduced (P < 0.01) by exercise in the corn oil and mixed corn-coconut oil fed groups. Plasma cholesterol and sterol excretion were unchanged by the exercise program.This investigation supported by Research Grant HE 08262 from the National Heart Institute, National Institutes of Health, U.S. Public Health Service.     

Dietary fish oil does not protect rats exposed to restraint or sleep deprivation stress

It has been suggested that fish oil (FO) prevents weight loss caused by physiological stress such as cancer, injury, or cardiovascular disorders. Previously, we observed that a high-fat diet containing corn and coconut oil exaggerated weight loss caused by the mixed physiological and psychological stress of repeated restraint (RR). This experiment tested the effects of a high-fat diet containing FO as the predominant lipid source in rats exposed to the mixed physiological and psychological stress of either RR or sleep deprivation (SD). FO did not prevent stress-induced hypophagia or weight loss in RR or SD rats but exaggerated the negative effects of stress on body weight in SD rats by promoting loss of lean body mass. RR caused a reduction in body fat content irrespective of dietary treatment. In SD rats, both stress and FO independently reduced body fat mass. FO did not have any effect on adrenal and thymus weights during RR or SD and did not influence corticosterone levels after 1 h of RR or after 48 or 96 h of SD. In conclusion, our results suggest that high levels of dietary FO do not improve the response to stress in rats exposed to mixed stressors.     

The effect of liver denervation on the consumption of various diets by rats

Liver afferents have been proposed to influence food intake control, however, previous studies have shown that chow (pellet) intake is apparently not altered in total liver denervated rats. The present study explored whether total liver denervation could alter the rats' intake of various diets other than chow pellets. Total liver denervations were verified using staining histological and monoamine histofluorescence techniques. The denervated and sham operated rats were given short-term (4-6 days) exposure to four diets: (diet 1, chow plus a 32% w/v sucrose-water solution; diet 2, 1:1 mixture of powdered chow and granular glucose; diet 3, 33% w/w Crisco and powdered chow mixture and diet 4, a 5% w/v glucose-water solution plus chow. Body weight gains were not affected-by either surgery or diet exposure. Daily consumptions of the diets were similar in both groups, nevertheless, there was a trend for the denervated rats to consume slightly more of a high fat diet, which lends support for one hypothesized liver satiety mechanism. Also, the denervated rats consumed less (an average 5 kcal/day) of the 5% glucose solution (one hypothesis tested would predict an increase consumption of glucose by the denervated rats). Thus the liver may play a role, albeit small, through several ill defined mechanism(s) in the regulation of feeding.     

Effect of dietary fats and proteins on drug metabolism

Rats were given diets ad libitum which varied in the amount (5 or 15%) and kind of fat [coconut oil (CNO) vs corn oil (CO)]. Animals were injected either with hexobarbital or pentobarbital and sleeping time was recorded. With animals eating a low fat diet, there were slight differences between the CNO vs CO groups. At the higher fat level, animals receiving the polyunsaturated diet slept more than twice as long as compared to animals eating a diet with saturated oil. Simultaneous injection with carbon tetrachloride significantly increased the sleeping time between the two dietary fat groups. Also, the kind of protein and level of fat in the diet had an influence on sleeping times. It was concluded that both the quality and quantity of fat as well as the quality of the protein can influence drug metabolism.     

Transient overconsumption of novel foods by deafferentated rats: effects of novel diet composition

We recently demonstrated that capsaicin-treated rats consume more of an unfamiliar high-fat diet than vehicle-treated controls, but only on initial exposure (Chavez et al, 1997). We hypothesized that negative feedback signals carried by capsaicin-sensitive visceral afferents are critical for the regulation of intake of novel foods, but redundant pathways take over during subsequent exposures. To examine the role of nutrient content of the novel diet, rats were systemically treated with capsaicin (n = 15) or vehicle (n = 10), and exposed to 1) a fat/olestra diet that was isocaloric with chow; 2) a readily accepted fat-free cake; and 3) pure corn oil. Each 3-h feeding trial was preceded by 24-h food deprivation. Treated rats did not overconsume familiar chow, but did consume 50% more than controls of both the fat/olestra diet and the corn oil on first exposure; this suggests that capsaicin eliminated visceral afferents that normally carry satiety signals. However, the effect with the fat/olestra mixture was due primarily to depressed intake by controls, unlike the pure fat diets; this apparent neophobic response was blunted in treated rats. Because treated rats failed to overconsume the fat-free cakes, the neural system damaged by capsaicin appears to be linked to energy or fat sensory mechanisms, and possibly to hedonic responsiveness.