A 91-day feeding study in rats with heated olestra/vegetable oil blends

Effect of Consumption Heated Oils with or without Dietary Cholesterol on the Development of Atherosclerosis

Heating oils and fats for a considerable length of time results in chemical reactions, leading to the aggravation of a free radical processes, which ultimately contributes to atherosclerosis. Our study focused on elucidating the effect of feeding heated oils with or without dietary cholesterol on the development of atherosclerosis in rabbits. We heated palm olein and corn oil at 180 °C for 18 h and 9 h per day, respectively, for two consecutive days. Next, 20 male rabbits were divided into four groups and fed the following diet for 12 weeks: (i) heated palm olein (HPO); (ii) HPO with cholesterol (HPOC); (iii) heated corn oil (HCO); and (iv) HCO with cholesterol (HCOC). Plasma total cholesterol (TC) was significantly lower in the HCO group compared to the HCOC group. Atherosclerotic lesion scores for both fatty plaques and fatty streaks were significantly higher in the HCO and HCOC groups as compared to the HPO and HPOC groups. Additionally, fibrous plaque scores were also higher in the HCO and HCOC groups as compared to the HPO and HPOC groups. These results suggest that heated palm oil confers protection against the onset of atherosclerosis compared to heated polyunsaturated oils in a rabbit model.

Effects of Polar Compounds Generated from the Deep-Frying Process of Palm Oil on Lipid Metabolism and Glucose Tolerance in Kunming Mice

In the present study, effects of deep-fried palm oil, specifically polar compounds generated during the frying process, on animal health including lipid and glucose metabolism and liver functions were investigated. Kunming mice were fed a high-fat diet containing deep-fried palm oil or purified polar compounds for 12 weeks. Their effects on animal health including hepatic lipid profile, antioxidant enzyme activity, serum biochemistry, and glucose tolerance were analyzed. Our results revealed that the consumption of polar compounds was related to the change of lipid deposition in liver and adipose tissue, as well as glucose tolerance alteration in Kunming mice. Correspondingly, the transcription study of genes involved in lipid metabolism including PPARα, Acox1, and Cpt1α indicated that polar compounds probably facilitated the fatty acid oxidation on peroxisomes, whereas lipid oxidation in mitochondria was suppressed. Furthermore, glucose tolerance test (GTT) revealed that a high amount of polar compound intake impaired glucose tolerance, indicating its effect on glucose metabolism in vivo. Our results provide critical information on the effects of polar compounds generated from the deep-frying process of palm oil on animal health, particularly liver functions and lipid and glucose metabolism, which is important for the evaluation of the biosafety of frying oil.

Caprenin 2. Short-Term Safety and Metabolism in Rats and Hamsters

A series of short-term feeding studies was undertaken to evaluate the biological effects of three behenic medium-chain triglycerides (BMCTs), including caprenin (CAP). All three triglycerides were composed primarily of caprylic (C8:0), capric (C10:0), and behenic (C22:0) acids, although total fatty acids compositions differed slightly. In the first experiment, adult male rats were maintained for 23 days on semipurifled diets containing 26% (w/w) of a BMCT, medium-chain triglyceride (MCT) oil or corn oil. Each triglyceride was assessed for its effects on growth, feed efficiency, calcium and iron balance, fat balance, and carcass fatty acid composition. A 28-day study of similar design evaluated the nutritive properties of chow diets that were supplemented with 15% of a BMCT or MCT when consumed by adult male golden Syrian hamsters. Finally, a 28-day feeding study in weanling male and female rats was conducted to assess the potential oral toxicity of CAP. CAP was administered in semipurifled diet at 0, 5, 10, and 15%. Corn oil was added at 18, 13, 8, and 3%, respectively, to maintain total dietary fat content at 18% and provide a source of essential fatty acids. The overall results of these experiments demonstrated that (1) BMCTs, including CAP, provided usable energy to sustain growth in rats and hamsters, although these triglycerides had lower calorie values than typical fats and oils, (2) up to 75–82% of the behenic acid content of BMCTs was unabsorbed by both species and excreted in the feces, (3) increased fecal excretion of BMCT-derived behenic acid did not significantly affect calcium and iron balance in rats, (4) behenic acid was metabolized readily by both rats and hamsters as indicated by recovery of only 3–15 % of the absorbed fatty acid in total carcass fat at the end of the studies, and (5) CAP was nontoxic to rats when consumed for 28 consecutive days at levels of up to 15% in the diet (83% of total dietary fat).

Review of the effects of dilution of dietary energy with olestra on energy intake

The non-absorbable substitute for dietary triacylglycerol, olestra, has been marketed in the United States for fifteen years. Olestra is comprised of sucrose with six to eight of its hydroxyl groups forming ester links with long-chain fatty acids. Because olestra is not hydrolyzed by fat-splitting enzymes in the small intestine, it is not absorbed from the small intestine into blood and tissues, and therefore provides no energy that can be utilized by the body. The hedonic properties of olestra with a specific fatty acid composition are similar to those of a triacylglycerol with the same fatty acid composition. Its use by consumers has been restricted by federal regulation to the commercial preparation of savory snack food items, principally as a frying medium for potato chips. An important question about the substitution of olestra for absorbable fat in the diet is whether the consumer will sense that a smaller amount of energy has been ingested. If it is sensed, thereby providing no satiation, then consuming additional energy in later meals will compensate for the removal of absorbable energy from the diet. If it is not sensed at all, then there is no compensation, and the person reduces caloric intake. This review first summarizes studies with olestra that have focused on its effect on the physiology of appetite. In general these studies have demonstrated that olestra does not influence signals of satiation including cholecystokinin and stomach emptying. The review then discusses studies of food consumption in experimental animals in which olestra was substituted for fat in the diet. Rodents have been repeatedly observed to compensate completely for the substitution of olestra for normal fat by eating more total diet. Most studies of the effect of olestra on human satiation have found incomplete or no compensation through additional energy consumption when olestra was substituted for dietary fat. In two clinical studies, however, complete compensation was observed, suggesting that experimental conditions and individual variability influence the ability to sense the substitution of olestra for absorbable fat. There is no evidence that dietary olestra causes consumption of more energy than would have been consumed without olestra in the diet. The data from animals and humans strongly suggest that the rodent is not a satisfactory model for the human in the determination of the extent of compensation by substitution of olestra for dietary fat.

Long term feeding effects of heated and fried oils on lipids and lipoproteins in rats

Long term feeding effects (20 weeks) of heated and fried oils at 5 and 20% level in the diet on growth, plasma and tissue lipids were studied in rats. Three vegetable oils of widespread usage viz., peanut oil, sesame oil and coconut oil with varying saturation and unsaturation were chosen for the study. No significant difference in growth rate, feed efficiency ratio, and liver weights were observed. Higher plasma cholesterol levels were observed in heated oil fed group of rats compared to corresponding fried oil groups. Low levels of HDL-c and increased LDL-c and VLDL-c were noted in heated/fried oil groups. Significantly low levels (p < 0.001) of triglyceride were observed in heated/fried sesame oil group of rats. No significant change in phospholipid was observed in any of the groups. Significantly low levels of liver cholesterol and high triglyceride levels (at 20%) were observed in coconut oil group. The fatty acid composition of plasma and liver reflected the type of diet consumed. Although linoleic acid levels were quite low in some of the heated/fried oil groups the arachidonic acid levels were quite high indicating repair mechanism. The results of the study however do not present any deleterious effect on growth, plasma and tissue lipid profile of rats as the conditions employed for heating/frying were not too drastic and the oils were not heat abused.

Cyclic fatty acid monomers from dietary heated fats affect rat liver enzyme activity

This study was conducted to investigate the effects of dietary cyclic fatty acid monomers (CFAM), contained in heated fat from a commercial deep-fat frying operation, on rat liver enzyme activity. A partially hydrogenated soybean oil (PHSBO) used 7 d (7-DH) for frying foodstuffs, or 0.15% methylated CFAM diets was fed to male weanling rats in comparison to a control group fed a nonheated PHSBO (NH) diet in a 10-wk experiment. All diets were isocaloric with 15% fat. Animals fed either CFAM or 7-DH diets showed increased hepatic content of cytochrome (cyt.) b5 and P450 and increased activity of (E.C. 1.6.2.4) NADPH-cyt. P450 reductase in comparison to the control rats. In addition, the activities of (E.C. 2.3.1.21) carnitine palmitoyltransferase-I and (E.C. 1.1.1.42) isocitrate dehydrogenase were significantly decreased when compared to that of rats fed the NH diet. A significantly depressed activity of (E.C. 1.1.1.49) glucose 6-phosphate dehydrogenase was also observed for these animals compared to the control rats fed NH diet. Moreover, liver and microsomal proteins were significantly increased when CFAM or 7-DH diets were fed to animals in comparison to controls while liver glycogen was decreased significantly in experimental groups of rats. The results obtained in this study indicate that the CFAM in the diet from either synthetic sources or used fats increase the activity of liver enzyme systems that detoxify them.

Influence of dietary vitamin E and oxidised sunflower oil on the storage stability of cooked chicken muscle

1. The effects of oxidised dietary sunflower oil and dietary alpha-tocopheryl acetate supplementation on alpha-tocopherol concentrations in broiler muscle and on the storage stability of refrigerated, cooked, minced muscle were determined. Broiler chicks were fed on diets containing fresh sunflower oil and 30 (FS30) or 200 (FS200) mg alpha-tocopheryl acetate/kg, or oxidised sunflower oil and 0 (OS0), 30 (OS30) or 200 (OS200) mg alpha-tocopheryl acetate/kg. 2. Inclusion of oxidised sunflower oil significantly reduced dietary and hence, muscle alpha-tocopherol concentrations. 3. Oxidised oil increased oxidation in raw and cooked muscle, and reduced the oxidative stability of muscle during refrigerated and frozen storage. 4. Supplementation with alpha-tocopheryl acetate improved the stability of muscle, with stability increasing as muscle alpha-tocopherol concentrations increased, when fresh or oxidised oil was fed. Supplementation with 200 mg alpha-tocopheryl acetate/kg offset the effects of oxidised oil in breast, but not in thigh. 5. The results show that the prooxidising effects of oxidised oils in muscle foods can be overcome, but alpha-tocopherol content needs to be adequately adjusted to compensate for increased oxidative stress. Supplementation with 200 to 400 mg alpha-tocopheryl acetate/kg may be necessary to achieve an optimum muscle alpha-tocopherol concentration.

Randomized, double-blind, placebo-controlled, consumer rechallenge test of Olean salted snacks

Olestra is a zero-calorie fat substitute that is neither digested nor absorbed. A randomized, double-blind, placebo-controlled, within-subject, crossover rechallenge study was conducted to compare the occurrence of gastrointestinal symptoms after ingestion of chips made with Olean brand of olestra or conventional triglycerides in subjects who had previously experienced gastrointestinal symptoms they attributed to consuming Olean. A total of 57 male or female subjects received 2 oz of Olean potato chips or triglyceride potato chips at each of four weekly site visits. The occurrence of gastrointestinal effects after product consumption was noted in follow-up telephone interviews 3 to 5 days after each visit. There was no significant difference in the frequency of any gastrointestinal symptoms (abdominal cramping, diarrhea, loose stools) following consumption of Olean chips or triglyceride chips, and the severity of diarrhea, loose stools, and abdominal cramping was similar. We conclude that consumption of a 2-oz serving of Olean chips is no more likely to result in reports of gastrointestinal symptoms than consumption of triglyceride snacks as a part of the usual diet, even in individuals who have claimed intolerance to Olean. The data suggest that subjects who previously experienced symptoms that they attributed to consuming products made with Olean may have mistakenly attributed their symptoms to these products.

Olestra, a nonabsorbed, noncaloric replacement for dietary fat: a review

Olestra has been shown to be safe for its intended use by extensive testing in animals and in humans. It is not digested or absorbed and has no effect on the structure or physiology of the GI tract, the only organ of the body that it contacts. Olestra can interfere with the absorption of other lipophilic substances from the GI tract. The interference occurs because a portion of those molecules that are sufficiently lipophilic partition into the nonabsorbed olestra and is carried out of the body. Whether olestra will interfere with the absorption of a specific molecule can be predicted from the octanol-water partition coefficient of the molecule, a parameter that can be measured or calculated from a knowledge of the structure of the molecule. Olestra does not affect the absorption or efficacy of oral drugs because, in general, they are not sufficiently lipophilic to partition into the olestra. Olestra does not affect the absorption of water-soluble micronutrients or the absorption and utilization of macronutrients. Olestra can reduce the absorption of the fat-soluble vitamins when olestra foods and the vitamins are coingested. These effects can be offset by adding specific amounts of the vitamins to foods made with olestra. Other than the carotenoids and vitamins A and E, olestra does not affect the absorption of potentially beneficial components of fruits and vegetables. The effects on the vitamins can be offset by adding the vitamins to olestra foods. The reduction in the absorption of carotenoids will be less than 6-10% when olestra snacks are eaten under free-living dietary patterns. Any effect this reduction has on vitamin A status can be offset by addition of vitamin A to the foods. The absorption of flavonoids, polyphenols, and most other phytochemicals in fruits and vegetables, which have been shown to provide beneficial health effects, will not be affected by olestra because they are not sufficiently lipophilic. Individuals consuming large quantities of olestra may experience mild or moderate common GI symptoms such as loose or soft stools, gas, or nausea, symptoms similar to those experienced with certain other foods or changed dietary habits. When olestra snack foods are eaten under free-living dietary patterns, the symptoms are not different from those experienced when eating full-fat snack products, in either incidence or severity. When they are experienced, the symptoms resolve in 1-2 days, but may recur. They do not worsen with continued or increased olestra consumption and pose no health risk to the consumer. Olestra products will carry an information label alerting consumers to the possibility of GI symptoms. Olestra foods provide an additional option to those individuals who want or need to lower their total energy intake and body weight. These individuals will find it easier to change dietary habits and to maintain healthful nutritional practices when they use olestra foods. For those who want or need to reduce fat intake but not lose weight, olestra foods can reduce fat intake without affecting energy. Because olestra foods have taste and other organoleptic properties that are similar to those of full-fat foods, individuals will find it easier to switch to low-fat diets.

Effect of replacement of fat by nonabsorbable fat (sucrose polyester) in meals or snacks as a function of dietary restraint

The effect of replacement of fat by nonabsorbable fat on energy intake and on feelings of hunger and satiety was assessed, in normal-weight dietary-restrained (n = 11), dietary-unrestrained (n = 13) and in postobese dietary-restrained women (n = 12), using 2 experimental designs. First, during breakfast and lunch on 2 sequential weekdays, 23 g of dietary fat was replaced by 23 g of a nonabsorbable fat. Second, dietary fat was replaced by a nonabsorbable fat in snacks consumed ad lib during a different week. Fat replacement in meals or in snacks did not result in changes in hunger and satiety ratings throughout the day. Replacement in meals yielded an energy intake reduction of 0.5 MJ/day (not significant) in dietary-unrestrained and in postobese dietary-restrained subjects; this reduction included 44% energy intake compensation. In normal-weight dietary-restrained subjects, energy intake reduction of 0.7 (p < 0.05) MJ/day was observed; this reduction included 22% energy intake compensation. Moreover, fat replacement in meals showed a shift in macronutrient composition from 35-40% energy from fat to 31-32% energy from fat. Replacement in snacks yielded an energy intake reduction of 0.4-0.5 MJ/day (not significant) in normal-weight dietary-restrained subjects and a reduction of 0.6-0.7 (p < 0.05) MJ/day in dietary-unrestrained and in postobese dietary-restrained subjects. In this situation, energy intake from snacks consisted of 48-78% energy from reduced-fat reduced-energy snacks, which implied a replacement of 10-15 g fat by 10-15 g SPE (sucrose polyester) and a shift in macronutrient composition from 35-40 percentage energy from fat to 33-36 percentage energy from fat. These results suggest short-term beneficial effects of fat replacement on energy and fat intake.

Genotoxicity and subchronic toxicity studies with heated olestra

Olestra is a class of sucrose-fatty acid polyesters intended for use as a non-caloric replacement of edible oil. Genotoxicity and subchronic toxicity studies were conducted to determine whether olestra could form genotoxic or toxic breakdown products during simulated commercial use. Heated olestra was prepared for these studies by batch-frying potato slices in olestra at 177-185 degrees C for 25-32 hr over 5-7 days. Genotoxicity of this previously heated olestra was assessed in four standard in vitro assays: (1) Salmonella mutagenesis (Ames test); (2) forward mutagenesis of mouse lymphoma cells at the thymidine kinase locus; (3) unscheduled DNA synthesis in rat hepatocytes; and (4) clastogenicity in cultured Chinese hamster ovary cells. These tests were conducted with previously heated olestra at concentrations up to at least 5 mg/ml both in the absence of exogenous bioactivation and, for assays (1), (2) and (4) with added liver microsomal (S-9) activation. The Ames and mouse lymphoma assays were performed with olestra (10 mg/ml and 23 mg/litre, respectively) either alone or emulsified with the non-toxic, non-ionic surfactant Pluronics F68, both in the presence and absence of metabolic activation. To test for clastogenicity in vivo, rats were administered previously heated olestra by gavage at 5 g/kg per day for up to 5 days and bone marrow cells were examined for chromosomal aberrations. Heated olestra lacked genotoxic activity detectable by the aforementioned assays. Heated olestra was fed to Fischer 344 rats at up to 10% of the diet (w/w) for 91 days. Evaluation of survival, food consumption, feed efficiency, physical condition, body weight, organ weight, haematological and clinical chemistry parameters, and histomorphology revealed no adverse effects attributable to ingestion of heated olestra at exposure levels in excess of those anticipated for human consumption. It is concluded that olestra used as a deep-frying medium conveys no genotoxic or toxic hazard at anticipated levels of human consumption.

Lipid-based fat substitutes

Fats and oils account for 38% of the total calories in the diet of Western populations, especially in the U.S. They provide the most concentrated source of energy, 9 kcal/g of a triacylglycerol molecule compared with 4 kcal/g provided by carbohydrate and protein. In response to consumer demands for low-calorie or calorie-free fats and their reluctance to give up the taste of fat, current research efforts have been directed toward the development of lipid-like fat substitutes. These fat substitutes contain the fatty acids found in conventional fats and oils, with all the physical and organoleptic properties of fats, but provide few or no calories in the diet. Some of the fat substitutes are modified triacylglycerols (glycerol backbone) with reduced digestion and absorption; others are digestible and nondigestible carbohydrate fatty acid esters and polyesters, respectively. Sucrose polyester (Olestra), a sucrose molecule esterified with six to either fatty acids, is the most studied of the lipid-based fat substitutes containing a carbohydrate backbone. If approved by the FDA, sucrose polyester will find application in almost all fat-containing foods. Specialty fats or fat substitutes targeted to certain individuals with special needs are being developed. Among these are the medium-chain triacylglycerols and structured lipids (glycerol backbone), or ¿nutraceuticals¿ with reduced absorption and medical applications. Enzyme biotechnology is another tool available to lipid chemists to selectively modify, esterify, transform, transesterify, and interesterify fats and oils or synthesize new lipids such as structured lipids of food, nutritional, and medical importance. These designer fats may be the trend in the future to produce medical lipids that do not occur normally in nature. The different types of lipid-based fat substitutes are reviewed with respect to their synthesis, analysis, metabolism, potential applications/uses, and the future of fat substitutes.

Lipid oxidation products in food and atherogenesis

Lipid oxidation products are present in unknown amounts in the food supply of industrialized societies. Evidence for a putative role of some of these compounds in accelerating events in the atherogenic process--the initiation of endothelial injury, the accumulation of plaque, and the termination phase of thrombosis--comes from both animal and human studies. Although metabolic and epidemiological studies in humans and animals generally support the concept that a higher intake of polyunsaturates is beneficial to lipoprotein metabolism and cardiovascular health, some findings suggest that a diet high in polyunsaturated fatty acids that are insufficiently protected by antioxidants, such as vitamin E, may carry a higher risk of atherosclerosis. Although gross pathological effects of ingestion of lipid oxidation products are unlikely in the human feeding situation, more subtle metabolic actions of these compounds on vitamin E status, platelet activity, and lipoprotein metabolism cannot yet be discounted. The presence of reactive lipid oxidation components in foods needs more systematic research in terms of the metabolic effects of these compounds and their occurrence in the usual diet, as well as the associated antioxidant requirements.

Routes of formation and toxic consequences of lipid oxidation products in foods

Lipid oxidation in foods is initiated by free radical and/or singlet oxygen mechanisms which generate a series of autocatalytic free radical reactions. These autoxidation reactions lead to the breakdown of lipid and to the formation of a wide array of oxidation products. The nature and proportion of these products can vary widely between foods and depend on the composition of the food as well as numerous environmental factors. The toxicological significance of lipid oxidation in foods is complicated by interactions of secondary lipid oxidation products with other food components. These interactions could either form complexes that limit the bioavailability of lipid breakdown products or can lead to the formation of toxic products derived from non-lipid sources. A lack of gross pathological consequences has generally been observed in animals fed oxidized fats. On the other hand, secondary products of lipid autoxidation can be absorbed and may cause an increase in oxidative stress and deleterious changes in lipoprotein and platelet metabolism. The presence of reactive lipid oxidation products in foods needs more systematic research in terms of complexities of food component interactions and the metabolic processing of these compounds.

Safety evaluation of olestra, a nonabsorbed, fatlike fat replacement

Olestra is the mixture of the hexa-, hepta-, and octa-esters of sucrose with long-chain fatty acids from any edible oil. Its physical properties are comparable to those of triglycerides, but it is not digested by lipolytic enzymes or absorbed and therefore is noncaloric. Technically, it can replace fat in a wide variety of foods and can be used to make cooked, baked, and fried foods lower in fat and calories. A Food Additive Petition is under review by the FDA, which is comprised of results of extensive testing in animals and humans. The major areas of investigation are metabolism and absorption, chronic toxicity, mutagenicity, carcinogenicity, reproductive and developmental toxicity, safety for gastrointestinal tract, nutrition, and the potential for olestra to affect absorption of drugs. This testing involved studies in five different species of animals and over 30 clinical investigations. The results of this research support the safety of olestra for use in foods.

A 20-month olestra feeding study in dogs

Three groups of beagle dogs (five/sex/group) were fed olestra, a mixture of octa-, hepta- and hexa-esters of sucrose formed with long-chain fatty acids, at 0, 5 or 10% of the diet for 20 months. The objective of the study was to assess the potential chronic toxicity of olestra in a non-rodent species. The feed was supplemented with vitamins A and E to ensure that the diets were nutritionally adequate and comparable for all groups. The levels of supplementation were established in a 91-day feeding study. Survival was 100% and growth was not affected by olestra. Olestra-fed animals consumed more feed than controls, apparently to compensate for the caloric dilution of the diet by olestra, but the increases were generally not statistically significant. No biologically significant changes were seen in haematological or serum biochemical parameters or in vitamin D and vitamin K status of the animals. Histopathology revealed no olestra-related effects. Isolated incidences of soft stools, apparently resulting from the large amounts of undigested olestra, were noted in olestra-fed animals. The results of this study indicate that olestra was not toxic when fed to dogs at up to 10% of the diet for 20 months.

Analysis of liver tissue for olestra following long-term feeding to rats and monkeys

The potential for olestra to be absorbed and to accumulate in tissues was investigated by analysing liver tissue from rats and monkeys in long-term feeding studies using sensitive chromatographic methods. Studies with intravenously administered olestra indicated that absorbed olestra is predominantly taken up by the liver. In monkeys, 74% of the injected dose was detected in the liver, as intact olestra, 48 hr after dosing. In rats, 58-96% of the injected dose was found in the liver, as intact olestra, within 24 hr. No olestra was detected (limit, 34 micrograms/g) in the livers of 14 monkeys fed olestra at 8% of the diet for 29 months. Also, no olestra was found in samples of liver, heart, kidney, spleen, lymph nodes and adipose tissues from 26 monkeys fed olestra at 0, 2, 4 or 6% of the diet, in random order, for consecutive 2-month periods. No olestra was detected in the livers of 47 out of 50 rats fed olestra at levels of up to 9% of the diet for up to 2 years. The amounts (2-4 micrograms/g) detected in the other three rats were near the detection limit of the chromatographic method (1.6 micrograms/g). The results show that accumulation of olestra in the liver, the primary target organ for absorbed olestra, was less than 3 x 10(-6)% of the total amount eaten by rats over 24 months and less than 4 x 10(-5)% of the amount eaten by monkeys over 29 months. These results are consistent with previous studies which showed that olestra is essentially not absorbed from the gastro-intestinal tract.

Chronic toxicity and carcinogenicity studies of olestra in Fischer 344 rats

Two 2-year feeding studies were carried out in Fischer 344 rats with olestra, a mixture of the hexa-, hepta- and octaesters of sucrose formed with long-chain fatty acids. Olestra was fed at 0, 0.99, 4.76 or 9.09% (w/w) of the diet in the first study, and at 0 or 9.09% (w/w) of the diet in the second. Daily observations, feed consumption and body weights, ophthalmoscopic examinations, organ weights, serum chemistry, haematology, urinalysis and histopathological evaluations revealed no evidence of any adverse effects associated with olestra ingestion. Relative to controls, there was a higher incidence of basophilic liver foci in olestra-fed female rats at 12 months. At 24 months, foci were observed in most animals in all groups but were more numerous in olestra-fed females. The foci were not associated with hepatic tumours, alterations in liver function, or increases in liver weight and therefore not considered to represent a toxic response to olestra. Isolated statistically significant differences in mortality, mononuclear cell leukaemia, and pituitary adenomas were observed but were not considered to be related to olestra ingestion since they were not reproducible across the two studies, generally not dose responsive, not consistent between sexes, and the incidences were within the ranges for historical and contemporary laboratory controls. The results of the two studies show that olestra was not toxic or carcinogenic when fed to rats at up to 9% of the diet for 24 months.