Abstract
ABSTRACT Experimental conditions for measuring the effect of the noncaloric fat substitute olestra on the availability of dietary nutrients were established in the weanling domestic pig. To evaluate the tolerance of the pig for dietary fat levels similar to those in the human diet, groups were fed a standard corn-soy-based swine feed with and without 14% (30% of energy) added fat for 4 wk. To evaluate the adequacy of a purified diet to produce good growth, groups of pigs were fed purified diets providing 30% of energy from fat and micronutrients at 1, 1.3 or 1.6 times the NRC's requirements for 5-to 10-kg swine. Cumulative body weight gain, digestible feed efficiency and a lack of adverse effects showed that the pig can tolerate diets providing 30% of energy from fat and that a purified diet providing the NRC's requirements for micronutrients produces growth comparable to a nutritionally complete swine feed. To determine whether tissue concentrations of vitamins A, D, E and K in the pig respond to olestra and dietary concentrations of the vitamins, two groups were fed purified diet providing 1 or 1.6 times the NRC's requirements for micronutrients and 4.8% olestra. Significant increases occurred in the serum concentration of 25-hydroxyergocalciferol and liver concentrations of retinol and a-tocopherol 

Olestra, a mixture of hexa-, hepta-and octaesters of sucrose tissue concentrations of the lipophilic nutrients cholesterol formed from long-chain fatty acids isolated from edible oils, and vitamins A, D and E, but not vitamin K (Jandacek et al. has cooking characteristics similar to those of traditional di-1990 , Jones et al. 1991a , Mattson et al. 1976 , etary fats and oils (Bernhardt 1988) . Olestra and triglycerides Mellies et al. 1983 . It has been shown in animals have similar thermal stability profiles (Kester 1993) . Olestra that the effect of olestra on the availability of the fat-soluble does not undergo lipolysis in the gut and is not absorbed intact vitamins can be offset by introducing additional amounts of Nolen 1972, Mattson and Volpenhein 1972, the vitamins into the diet (Lafranconi et al. 1994 ). Miller et al. 1995) ; therefore it contributes no energy to the Jandacek (1982) proposed that the absorption of highly diet. Because of its unique properties, olestra can serve as a lipophilic substances would be affected by olestra because such zero-calorie replacement for conventional fats and oils.

substances partition into the olestra in the gastrointestinal The evaluation of Olestra (Olean, Proctor & Gamble, Cin-(GI) 4 tract and thus are not available to the intestinal micelles. cinnatti, OH) for use as a replacement for dietary fat in foods This partitioning would not be expected to occur with waterincludes determination of its effect on the availability of disoluble nutrients; therefore olestra would not be expected to etary nutrients. Olestra has been shown to reduce affect the absorption of these nutrients. The domestic pig was chosen as the model in which to investigate the potential nutritional effects of olestra. The pig GI anatomy, morphology and physiology. The GI tract of a ling pig are similar to or greater than those of children 1-3 y of age (Middleton et al. 1997) . Finally, the sizes of the various 30-to 40-kg pig is similar in total length to that of an adult human (Leigh-Browne and Harpur 1975) and the relative sizes digestive organs of the two species at birth are markedly similar (Moughan et al. 1992 ) and the weanling pig's body size, 10-of sections of human and pig GI tracts are similar (KuriharaBergstrom et al. 1986 ).

12 kg, is similar to that of a child. Some key aspects of human nutrition have not been modPigs and humans have similar gastric cell types and similar gastric villi (Kurihara-Bergstrom et al. 1986 ). The composition eled in the pig. These include the micronutrient content of the diet, the level of fat in the diet, the chemical forms and and control of gastric secretions are similar in the two species (Kidder and Manners 1978) as are ingesta transit times (Miller concentrations of nutrients, the response of vitamin D status to UV light exposure and meal-eating pattern. These condiand Ullrey 1987).

Digestive and absorptive abilities of the pig are similar to tions were investigated in this study. The general purpose of the study was to evaluate the appropriateness of the pig as those of humans (Bjorkman et al. 1984 , Forsum et al. 1981 , Graham and Aman 1987 , Juste et al. 1983 a model for determining the effects of olestra on nutrient availability. Specific objectives were as follows: 1) to evaluate ners 1978). Both species depend on dietary quality because gut microflora play a relatively minor role in modifying nutrients in the pig's tolerance for dietary fat levels similar to those in the human diet; 2) to evaluate the adequacy of a purified diet to the diet (Miller and Ullrey 1987) . The requirements of the weanling pig for nutrients are similar to or greater than human produce good growth; 3) to determine whether tissue concentrations of vitamins A, D, E and K respond to changing dietary requirements Ullrey 1987, Pond and Houpt 1978) ; thus the pig is a good model for subgroups of the population concentrations of the vitamins and to olestra; and 4) to determine how much exposure to UV light is required to produce with high nutrient demands such as children and pregnant or lactating women (Middleton et al. 1997) . Pigs reach sexual a vitamin D 3 contribution to total vitamin D status representative of the normal human situation. maturity and display reduced growth by 6-8 mo of age (Anderson 1974) ; thus it is possible to conduct studies over reasonable periods of time covering the major growth and developmental MATERIALS AND METHODS phases of the pig's life.

This study was conducted according to the U.S. Food and Drug
Pigs have been used extensively in pediatric nutritional
Administration's Good Laboratory Practice Regulations for Noncliniresearch (Cooper 1975, Glauser 1966, Mellor and Cockburn cal Laboratory Studies. All procedures involving the pigs were con-1986, Moughan et al. 1992, Schneider and Sarett 1966 1 The 1 NRC and 1.6 NRC diets containing 4.8% olestra had the same composition as the 1 NRC and 1.6 NRC diet, respectively, except that 48 g of olestra were added to 1 kg of diet. The digestible energy content of the diets containing olestra was 17.5 MJ/kg.
Pigs have been used extensively in pediatric nutritional
2 All ingredients were from ICN Biomedicals (Cleveland, OH) except olestra, which was provided by the Procter & Gamble Co. (Cincinnati, OH).
Pigs have been used extensively in pediatric nutritional
The pigs had been weaned at Ç3 wk of age and fed a standard cornTest groups and diets. The compositions of the diet fed the pigs are shown in Table 2 . To evaluate the pig's ability to tolerate a soy-based starter diet formulated by the University of Wisconsin dietary level of fat comparable to the recommended level in the Swine Unit.
Pigs have been used extensively in pediatric nutritional
human diet, one group of pigs was fed a nutritionally complete cornUpon receipt, the pigs were housed in groups of six or seven in soy-based pig feed from the Swine Nutrition Department at the 0.9 1 2.5 M pens for 2 wk. During the first week of this acclimation University of Wisconsin-Madison (standard group). A second group period, the standard starter diet was provided. During the second was fed the same corn-soy-based feed modified to provide 30% of week, the pigs were fed a purified basal diet containing the NRC energy from fat (high fat group), the recommended level for the requirements for micronutrients for 5-to 10-kg pigs (NRC 1988) and human diet (U.S. Department of Health and Human Services 1988). 14% (wt/wt) fat, which provided 30% of the total digestible energy.
Pigs have been used extensively in pediatric nutritional
This high fat diet provided the same levels of micronutrients, limiting During the acclimation period, the pigs were given a detailed amino acids and proteins per kilocalorie of digestible energy as the physical examination and a limited clinical pathology screening, and standard feed. were observed daily for abnormalities indicating ill health. Only aniTo evaluate the adequacy of a purified diet to support growth, mals with normal clinical pathology were selected for the treatment three groups of pigs were fed purified diet containing 1, 1.3 or 1.6 phase of the study.
Pigs have been used extensively in pediatric nutritional
times the NRC requirement levels of micronutrients (1 NRC, 1.3 At the start of treatment, the pigs were placed into individual NRC and 1.6 NRC groups) and 30% of energy from fat. The dietary pens in a sunlight-free facility with a 12-h light:dark cycle maintained concentrations of micronutrients and protein were based on the NRC by incandescent lights. The temperature of the facility was kept above requirements for 5-to 10-kg swine (NRC 1988) , the body weight 18ЊC; humidity was not regulated. The pens were cleaned once or range of the pigs at the start of the study. The 1.3 NRC diet provides twice daily to reduce the potential for coprophagy.
Pigs have been used extensively in pediatric nutritional
nutrients at levels similar to those in a human diet containing the Treatment groups. Twelve pigs, six males and six females, were Recommended Dietary Allowances (RDA) of nutrients because the selected randomly and killed at the end of the acclimation period RDA for most nutrients is set above the average requirement by an to provide base-line tissue vitamin concentrations. Eighty pigs were amount sufficient to meet the needs of almost all members of the assigned randomly to one of nine treatment groups, balanced by body population, often 2 SD above the average (NRC 1989) . For most weight. Seven groups contained eight pigs each, two control groups nutrients, the SD is Ç15% of the mean (Guthrie 1989). The 1 NRC contained 12 each. Every group contained equal numbers of males and 1.6 NRC diets provide nutrients at levels that bracket the levels and females. The treatment groups are listed in Table 1 in regard to in the 1.3 NRC diet. the specific objectives of the study.
Pigs have been used extensively in pediatric nutritional
The composition of the 1 NRC diet is shown in Table 2 . The Olestra. The olestra was synthesized by the method of Rizzi and compositions of the 1.3 and 1.6 NRC diets were the same as that of Taylor (1978) . The sample consisted of ú99% octa-, hepta-and the 1 NRC diet except that the amounts of the vitamin-mineral hexaesters. The relative composition of the fatty acids making up the premix were increased from 8.0 to 10.4 or 12.8 g/100 g diet, respecacyl groups was 42% oleic, 28% linoleic, 19% palmitic, 6% stearic tively. In these diets, the amounts of Alphacel were decreased proporand 6% others. Before the olestra was added to the diet, it was heated tionally. The total amounts of Alphacel did not differ significantly to simulate its use in the commercial preparation of savory snacks among the three diets, however, because it was the major component (e.g., potato chips), its intended initial use. When olestra is heated, of the vitamin-mineral mix. Table 3 shows the compositions of the the same degradation processes and the same degree of degradation vitamin-mineral premixes used in preparing the diets. occur as when triglycerides are heated. For example, polymeric species
Pigs have been used extensively in pediatric nutritional
The amount of each micronutrient added to the purified basal diet are formed with the same intermolecular linkages as those found in was calculated from the NRC recommended dietary concentration by heated triglycerides and to the same extent, on a molar basis (Gardner adjusting for the metabolizable energy content of the basal diet (4172 and Sanders 1990 , Gardner et al. 1992 , Henry et al. 1992 . The kcal/kg, or 17.5 MJ/kg) relative to a standard pig feed providing 3240 amount of polymers formed during heating thus provides a measure kcal (13.6 MJ) of metabolizable energy per kilogram, on which the of the degree of degradation that occurs with prolonged heating. The NRC requirement is based. The digestible energy content of the test olestra was heated until it contained a polymer level similar to diets was calculated by summing the digestible energy contributed that found in vegetable oil used to fry potatoes under commercial per kilogram of diet by each dietary ingredient. The targeted amounts of nutrients in the purified diets are shown in Table 4 . frying conditions (Henry et al. 1992 ). by HPLC (Cort et al. 1983, Thompson and Duval 1989) . After sapon- The dietary concentration of ergocalciferol was determined from performed on a HPLC system equipped with a reverse-phase C-18
Pigs have been used extensively in pediatric nutritional
Alphacel, g 16.8 33.2 32.8 column (Dupont) and UV detector, using peak height measurement and linear regression from a standard curve.
Pigs have been used extensively in pediatric nutritional
1 Eighty grams of premix were added per kilogram of diet.
Pigs have been used extensively in pediatric nutritional
The dietary concentration of phylloquinone was measured by 2 Unless otherwise indicated, supplied by ICN Biomedical (Cleve-HPLC, following the method of Haroon et al. (1986) . Dietary lipids land, OH).
Pigs have been used extensively in pediatric nutritional
were extracted by the procedure of Bligh and Dyer (1959) . After none was converted to the hydroquinone with zinc metal and then extracted with acetonitrile. Chromatography was performed with dichloromethane:methanol as the mobile phase, a silica column (5-mm The concentrations of the nutrient were kept at the requirements ODS Zorbax, DuPont), and a fluorescence detector (Kratos). Dihyfor 5-to 10-kg pigs throughout the study. This was done to avoid a dro-vitamin K 1 was used as an internal standard. Phylloquinone conchange in nutrient intake during the study that might prevent tissue centration was determined by peak height measurement and linear concentrations of the fat-soluble vitamin from reaching steady-state regression from a standard curve. values. Further, the slight excess of nutrients fed to the pigs at the The concentration of olestra in the diet was measured by reversedend of the study, relative to the requirements for 5-to 10-kg pigs, phase liquid chromatography (Tallmadge and Lin 1993) . Dietary lipwould not prevent detection of an effect of olestra on nutrient status ids were extracted with 50:50 hexane/ethyl ether, dissolved in methylbecause nutrient stores were being measured and stores are proporene chloride and injected onto an octadecylsilane column (Zorbax tional to intake.
Pigs have been used extensively in pediatric nutritional
ODS, MAC-MOD Analytical, Chadds Ford, PA) equipped with an To determine whether tissue concentrations of the fat-soluble evaporative light-scattering detector (Applied Chromatography Sysvitamins respond to olestra and to changes in vitamin intake, two tems, MacClesfield, England). Olestra and triglycerides were sepagroups of pigs were fed either the 1 NRC or the 1.6 NRC purified rated by gradient elution using methylene chloride/acetonitrile as the diet containing 4.8% olestra [1 NRC(OA) and 1.6 NRC(OA) mobile phase. Concentration was determined by peak area measuregroups]. Olestra was added to, not substituted for, triglyceride in these ments and linear regression from a standard curve. diets; therefore the total digestible fat content of the diets was the The diets were prepared by ICN Biomedicals (Cleveland, OH) same in all groups.
Pigs have been used extensively in pediatric nutritional
and were shipped and stored at 020ЊC in plastic-lined, lightproof To determine the effect of UV light on vitamin D status, two containers under nitrogen until offered to the pigs. groups of pigs were fed purified diet containing 1.6 times the NRC Feeding regimen. The daily allotment of feed was offered to the requirements of micronutrients and were exposed to either 15 feeding period was offered again in the subsequent feeding. The total mm, Dupont) and UV detection. Retinol was detected at 325 nm; a-tocopherol was detected by fluorescence excitation at 292 nm and amount of uneaten feed was determined at the end of the day by weighing. Spillage around the feed bowls was collected and weighed emission at 325 nm. USP standards of all-trans-retinol and a-tocopherol were used to generate standard curves. along with the uneaten feed. On days when blood samples were taken, the morning feeding was delayed until after the sampling.
Pigs have been used extensively in pediatric nutritional
Serum concentrations of 25(OH)D 2 and 25(OH)D 3 were measured simultaneously by HPLC (Kao and Heser 1984) . The serum The daily allotment of feed offered to the pigs was calculated from the pig's body weight at the beginning of the week and the predicted samples were acidified with concentrated hydrochloric acid, and the 25-hydroxy metabolites extracted with prepacked octadecylsilano silweight gain over the week, using growth curves for the same strain of cross-bred pigs fed standard corn-soy-based swine feed (Martin ica cartridges (C-18 Bond Elute, Analytichem International, Harbor City, CA). Further purification was accomplished by reextracting on and Crenshaw 1989). To facilitate complete consumption of the daily feed allotment, the pigs were fed 95% of the NRC requirement for aminopropyl cartridges (NH 2 Bond Elute, Analytichem International). The metabolites were separated and quantified with a silica digestible energy based on body weight (NRC 1986) .
Pigs have been used extensively in pediatric nutritional
Measurement schedule. The pigs were examined twice daily for column (Zorbax, 5-mm, Dupont) and UV detection (Kratos Analytical). Concentrations of the two metabolites were calculated from a signs of vitamin deficiencies and for general health. Feed intake was determined daily. Body weights (BW) were determined and cumulasingle calibration curve established with a 25(OH)D 3 standard (Duphar, Amsterdam, The Netherlands). Recovery was determined for tive weight gain was calculated weekly. To take into account variability in body size at the start of treatment, the calculated cumulative each serum sample by adding a 25-hydroxy-(25[27]-methyl-3 H)cholecalciferol standard (Amersham, Arlington Heights, IL) to the samweight gain was ''normalized'' in two ways, by dividing by the wk-0 body weight (cumulative weight gain/wk-0 BW) and by dividing by ple before extraction. PT was measured weekly as part of the clinical chemistry battery. the body surface area at wk 0 (cumulative weight gain/wk-0 body surface area). The wk-0 body surface area was estimated as (wk-0 Statistical analysis. Biological response data, which included tissue concentrations of the vitamins and growth parameters, were ana-BW) 0.75 (Kleiber 1975) . Digestible feed efficiency, defined as [(kg BW gain/kcal digestible energy consumed) 1 1000], was calculated lyzed by one-way ANOVA for each sex and by two-way ANOVA using gender and diet as class variables. If no significant difference weekly.
Pigs have been used extensively in pediatric nutritional
Prothrombin time (PT) was measured weekly. Prothrombin time was found between the responses of males and females, intergroup comparisons were made on the combined data to provide increased was chosen as a measure of vitamin K status because it is the standard measurement used in the pig. More sensitive measures are available power for detecting group differences. The protected least significant difference test was used to make pairwise comparisons (Snedecor and for assessing vitamin K status in humans; those measures were used to develop data about the effects of olestra on vitamin K status in Cochran 1980). Pairwise comparisons were made for groups relevant to the specific objectives of the study. human studies (Schlagheck et al. 1997a and 1997b Measurements were made at base line, wk 2 and wk 4. Liver concenone half the detection limit, rather than zero, for the purpose of statistical analysis (Helsel 1990 ). trations of vitamin A (total retinol and retinyl esters) and vitamin E (a-tocopherol) were used as measures of the status of these vitamins.
Pigs have been used extensively in pediatric nutritional
The stability of dietary components was determined by regression analysis of mean values vs. time. Measurements were made for the group of pigs killed at base line and for all groups killed at the end of the study.
Pigs have been used extensively in pediatric nutritional
All analyses were conducted with SAS Version 5.18 or 6.06 software (SAS Institute, Cary, NC). All comparisons were made at the Biological measurements and methods. Blood was collected from the cranial vena cava after an overnight fast. The sera or plasma two-tailed 0.05 significance level. samples were stored at 020 { 10ЊC until analyzed. The pigs were killed by being rendered unconscious with a captive bolt pistol and The concentrations of vitamin A (total retinol and retinyl esters) diet decreased slightly over time; the trend was significant. No and vitamin E (a-tocopherol) in liver tissues were measured by HPLC such trend was present for the 1 NRC diet. This finding sugusing a method that allowed both vitamins to be determined simultagests that there was no significant degradation of b-carotene neously (Kayden et al. 1983 ). The samples were saponified with ethain the purified diets. NRC(OA) diet, determined from a single measurement at was not significantly different than the value measured in the group killed at base line. The liver concentration of vitamin each time point. Subsequent measurements made on the same purified diet over a period of 8 mo showed no change in olestra E for the pigs fed the 1 NRC diet was not significantly different than the value measured in the base-line group. concentration (Cooper et al. 1997b) , an indication that the trend observed here is unlikely to represent instability of olesOlestra produced significant reductions in the liver concentrations of vitamins A and E (Table 8) . Addition of 4.8% tra in these purified diets.
Pigs have been used extensively in pediatric nutritional
Health and growth of the pigs. All of the pigs completed olestra to the diet providing the NRC requirements for the two vitamins reduced liver vitamin A and vitamin E concenthe study. Daily observations revealed no signs of ill-health, nutritional deficiency or indications of intolerance to olestra trations by 55 and 66%, respectively. such as failure to eat or to grow. The pigs fed the diets con-TABLE 6 taining 4.8% olestra ate Ç29 g olestra/d during the first week of the study and Ç53 g olestra/d during the last week.
Cumulative weight gains for pigs fed standard feed or purified
No significant differences were found between males and diets with or without 4.8% olestra for 4 wk 1 females with respect to their pattern of growth; therefore the data were combined for intergroup comparisons. All groups Cumulative weight gain grew at the same rate. Cumulative weight gains at the end of the study are shown in the NRC requirements ( Table 8) . The liver concentration of 3 Wk-0 body surface area Å (wk-0 body weight) 0.75 (Kleiber 1975 to total vitamin D status models the human situation (Arnaud et al. 1977 , Delvin et al. 1979 of the fat substitute olestra on nutrient bioavailability. The week of the study is Ç17 times the average chronic intake of energy consumption.
Cumulative weight gains for pigs fed standard feed or purified
olestra estimated for humans consuming savory snacks prepared with olestra, 3.1 g/d, and Ç8 times the 90th-percentile intake, 6.9 g/d (Webb et al. 1997) . The initial intended use The serum concentration of 25(OH)D 2 , measured at the of olestra is in preparing savory snacks such as potato chips. end of the study, increased in a dose-responsive manner as Pigs fed a purified diet in which all micronutrient contents the concentration of ergocalciferol in the purified diet was met NRC requirements, with 30% of energy from fat, grew at increased from 1 to 1.6 times the NRC requirement ( Table  a rate equivalent to that produced by the standard swine feed 9). The trend was also present at wk 2. Relative to base line, with or without 30% of energy from fat. Olestra had no effect serum 25(OH)D 2 concentration increased by 2.5, 4.3 and 5.9 on growth. The pigs fed the purified diets, with or without times over the 4 wk of the study for pigs fed the 1 , 1.3 or 1.6 olestra, grew at the same rate and had the same feed efficiency. NRC diet, respectively.
Cumulative weight gains for pigs fed standard feed or purified
All of the pigs grew at essentially the same rate observed by Olestra significantly reduced the serum 25(OH)D 2 concenother researchers for the same crossbred strain fed a corntration when added to the 1 and 1.6 NRC diets. The mean soybean meal. During the last week of the study, for example, reduction was 33% for the pigs fed the 1 NRC diet.
Cumulative weight gains for pigs fed standard feed or purified
Effect of UV light on serum 25(OH)D 3 . Exposure of the pigs to UV light produced reciprocal changes in the serum (Table 6 ). In-
Concentrations of vitamin A and vitamin E in liver of pigs fed
creasing the daily amount of UV exposure produced the ex- For the pigs that were not exposed to UV light, serum 1 NRC (OA) 25.1 { 6.3 a 3.9 { 0.5 a
Concentrations of vitamin A and vitamin E in liver of pigs fed
To determine the amount of UV exposure needed to pro- equation resulting from the regression was as follows: were not compared statistically for those groups not exposed to UV light because most pigs had values below the analytical detection limit. To calculate group means, one half the detection limit, rather than zero, was used for those pigs (Helsel 1990) .
Concentrations of vitamin A and vitamin E in liver of pigs fed
2 Group designations indicate the diet fed, e.g., 1.3 NRC Å 1.3 times the NRC's requirements for micronutrients for 5-to 10-kg swine (NRC 1988) . OA Å with 48 g olestra added/kg diet; 15 UV and 45 UV indicate 15 or 45 min/d exposure to UV light, respectively.
Concentrations of vitamin A and vitamin E in liver of pigs fed
when the pigs weighed 25-30 kg, the growth rate for all groups cates that deficiencies in micronutrients present at close to required levels are sometimes manifested when the levels of other was about 5 kg/wk, the same rate that Martin and Crenshaw (1989) reported for 11-to 60-kg pigs of the same cross breed.
Concentrations of vitamin A and vitamin E in liver of pigs fed
nutrients are manipulated. This was the case for vitamin K in the AIN-76 diet for rats (Bieri 1980) and for potassium in domesThe purified diet providing vitamins A, D, E and K at or near the NRC requirements for 5-to 10-kg swine produced tic cats fed purified diets with variable protein concentration (Hills et al. 1982) . adequate but marginal stores of these vitamins. The pigs' vitamin stores were responsive to changes in dietary concentraBody weight gain and digestible feed efficiency were used as key measures of the adequacy of the dietary micronutrient tions of the vitamins and were affected by olestra in the diet. The serum concentration of 25(OH)D 3 responded to UV exlevels. These parameters are the most reliable overall indicators of micronutrient status when protein intake is sufficient posure.
Concentrations of vitamin A and vitamin E in liver of pigs fed
This is the first study in swine to show the adequacy of a diet and when energy intake is controlled, as in this study. Casein, a complete and easily digested source of amino acids and nitroin which all micronutrients were set to the NRC requirement level for swine. Purified diets composed of similar ingredients gen, was included in the purified diets at a level of 25%, enough to provide sufficient protein intake. Energy intake was have been developed and used previously for swine nutrition research, but those diets contained multiples of the NRC requirecontrolled at 95% of the NRC energy requirement for growing swine. Feeding at this level ensured that the pigs ate all or ments of some micronutrients (Cunha et al. 1994 , Heinemann et al. 1946 , Miller et al. 1965 . The adequacy of the 1 NRC diet nearly all of their daily feed allotment without experiencing a significant limitation in growth rate. fed in this study indicates that the micronutrient requirements, determined under conditions in which a single micronutrient is Because these pigs grew rapidly, they are a sensitive model in which to detect effects of substances on nutrient bioavaillimiting in the diet, are valid when all micronutrients in the diet are limited to their requirement level. This is significant in light of ability inasmuch as nutrient pools are expanding rapidly and nutrient demands to support growth are high. Growth was the numerous interactions known to occur among micronutrients (Machlin and Langseth 1988) . Experience in other species indimeasured for only 4 wk in this study, a length of time adequate to test the nutritional adequacy of a diet; however, a subsestance, than the availability of retinyl palmitate because bcarotene is more lipophilic. A measure of the lipophilicity of quent study has shown that the same pigs fed the 1 NRC diet used here maintained similar growth rates for up to 26 wk a molecule is its octanol-water partition coefficient (p c ). The value of the octanol-water partition coefficient is generally (Cooper et al. 1997b) . Therefore this diet is adequate for use in both short-and long-term studies.
Concentrations of vitamin A and vitamin E in liver of pigs fed
expressed as log 10 p c . Water-soluble molecules have log 10 p c values°0; lipid-soluble molecules have log 10 p c values ú.0. The use of a diet that provides micronutrients at or near the NRC requirement levels, as in this study, offers a rigorous
Concentrations of vitamin A and vitamin E in liver of pigs fed
The log 10 p c for b-carotene is 17.6; the value for retinol, the species absorbed when retinyl palmitate is eaten, is 7.6 (Cooper test of factors that affect nutrient availability because nutrient stores are proportional to intake in this range of dietary nutriet al. 1997d ). The greater effect of olestra on the absorption of b-carotene, in relation to the effect on the absorption of ent levels. The 1 NRC diet provided intakes that were adequate but not excessive. Feeding pigs a diet that provides nutriretinyl palmitate, has been shown in human studies (Daher et al. 1997b , Schlagheck et al. 1997a and 1997b ). ents at the NRC level of requirements, the 1 NRC diet, increases the possibility that an effect on any given Vitamin E was provided as dl-a-tocopheryl acetate, a source of vitamin E in the U.S. diet and a model compound for the micronutrient will be detected as a decrease in growth. Depressed growth is a common sign of nutrient deficiency.
Concentrations of vitamin A and vitamin E in liver of pigs fed
various isomers of the vitamin (Farrell 1988) . Vitamin D and vitamin K were provided as ergocalciferol and phylloquinone, The NRC requirement produces a lower level of nutrient status in the pig than the RDA produces in humans because respectively, major sources of these vitamins in the human diet. Menadione is the usual source of vitamin K in swine the RDA for most nutrients is set at a value sufficiently above the average requirement, usually 2 SD, to meet the needs of diets. If menadione were used instead of phylloquinone, however, the potential for olestra to affect vitamin K status in almost everyone in the population (NRC 1989) . Pigs fed a diet that provides micronutrients at the NRC requirement humans could not be detected because menadione is poorly soluble in lipids and thus unlikely to be affected by olestra. level thus model the situation in which humans consume marginal but adequate levels of micronutrients. Such individuals
Concentrations of vitamin A and vitamin E in liver of pigs fed
The log 10 p c for menadione is 2.2.
Concentrations of vitamin A and vitamin E in liver of pigs fed
Other conditions used in the study model human dietary are most at risk of nutritional deficiency if nutrient availability is further restricted.
Concentrations of vitamin A and vitamin E in liver of pigs fed
conditions. For example, the fat content of the diet was set at 30% of energy. This level was based on current dietary The 1 NRC diet provided adequate but not excessive fatsoluble vitamin status in ranges responsive to changes in availrecommendations for good health (U.S. Department of Health and Human Services 1988) and contrasts with the very low ability. The mean liver vitamin A concentration in the group fed the 1 NRC diet was 55.5 nmol/g liver. This liver concentrafat levels typically used in swine nutrition studies. A dietary fat level similar to that in the human diet is important when tion is sufficient to maintain normal plasma retinol concentrations in pigs (Hennig et al. 1985) but is below the 70 nmol/g investigating the availability of fat-soluble vitamins because of the role of fat in the absorption of these vitamins and in liver considered adequate in humans (International Vitamin A Consultative Group 1993). The mean liver vitamin E congastric emptying. Olestra had no effect on the digestion or utilization of fat based on the absence of an effect on growth centration in this group of pigs was 11.6 nmol/g liver. This is similar to values that other researchers have measured in pigs and digestible feed efficiency in the olestra-fed groups. Olestra has been shown not to significantly affect triglyceride absorpfed the NRC requirement of vitamin E in a purified diet, and higher than required to prevent clinical deficiency (Hoppe et tion in humans (Daher et al. 1997c ). The pigs were fed three meals per day to mimic the major al. 1993). The serum 25(OH)D 2 concentration for pigs fed the 1 NRC diet was adequate to prevent clinical deficiency and eating pattern in humans. Pigs given free access to feed eat 7-12 times during the day and usually do not consume large similar to values measured by other researchers in pigs fed the NRC requirement of vitamin D (Engstrom and Littledike amounts at any one time (Houpt and Houpt 1991) . In this study, the pigs adapted readily to the three-meals-a-day regi-1986). Vitamin K status, as measured by PT, was normal in the pigs fed the 1 NRC diet.
Concentrations of vitamin A and vitamin E in liver of pigs fed
men. Use of a meal-eating pattern similar to the human pattern is important inasmuch as eating patterns theoretically can afThe NRC requirement levels used for these and all other micronutrients were those for 5-to 10-kg pigs, the size of the fect the digestion and metabolism of nutrients. The pigs were exposed to UV light to stimulate the cutapigs at the start of the acclimation period. Even though NRC guidelines indicate that the requirements for micronutrients neous production of vitamin D 3 . Including both vitamin D 2 and vitamin D 3 as contributors to vitamin D status models the decrease as pigs age, the stores and tissue levels of vitamins A, D and E did not change substantially from the beginning human situation, in which vitamin D 3 is the primary contributor. Generally, dietary vitamin D 2 provides only 10-20% of to the end of the study. This finding supports the use of the 5-to 10-kg pig requirements for pigs up to at least 30 kg, the vitamin D status in humans (Arnaud et al. 1977 , Haddad and Hahn 1973 , Jones 1978 , Poskitt et al. 1979 . This study showed weight of the pigs at the end of this study. Use of a single level of nutrients prevents possible perturbations of steadythat a vitamin D 3 contribution to total vitamin D status typical of the human situation can be obtained in pigs by 1-2 min/ state vitamin concentrations in tissues.
Concentrations of vitamin A and vitamin E in liver of pigs fed
The chemical forms of the fat-soluble vitamin in the purid exposure to UV light. Exposure to UV light caused a reduction in the serum confied diets were chosen to be as relevant to human nutrition as was practical. Vitamin A was provided as a 3:1 mixture of centration of 25(OH)D 2 . The pigs fed the 1.6 NRC diet and exposed to UV light had lower serum 25(OH)D 2 concentraretinyl palmitate and b-carotene, typical of the average proportions and the forms of vitamin A in the U.S. diet (Olson tions than the pigs fed the 1.6 NRC diet and not exposed to UV light. A plausible explanation for this observation is 1983). Including b-carotene as a dietary source of vitamin A ensures that the full effect of a nonabsorbed lipophilic subcompetition between vitamin D 3 and vitamin D 2 for the liver 25-a-hydroxylase enzyme. In pigs, vitamin D 3 is the preferred stance, such as olestra, on vitamin A status will be measured. The interaction between olestra and lipophilic nutrients insubstrate for the liver enzyme (Horst et al. 1982) . As a result, an increase in the amount of vitamin D 3 available for hydroxylcreases as the lipophilicity of the nutrient increases (Jandacek 1982) . The availability of b-carotene should be more strongly ation might be expected to cause a decrease in serum 25(OH)D 2 concentration. Because of this interaction, the efaffected by olestra, or any other nonabsorbed lipophilic sub-

{'paper_id': '19070790', 'title': "The domestic pig as a model for evaluating olestra's nutritional effects.", 's2_url': 'https://api.semanticscholar.org/CorpusID:19070790', 'source': 'S2ORC'}