Olestra is the usual and common name for the mixture of hexa-, hepta- and octaesters of sucrose formed from long-chain fatty acids from edible oils. It has the physical, organoleptic and thermal properties of regular fats (Bernhardt 1988, Kester 1993). Olestra is not hydrolyzed by pancreatic lipases (Mattson and Volpenhein 1972) and is not absorbed intact from the gastrointestinal (GI) tract (Miller et al. 1995). Because of these unique properties, it can serve as a zero-calorie replacement for dietary fat. Olestra (Olean, Procter & Gamble, Cincinnati, OH) is approved for use in replacing 100% of the fat used to prepare savory snacks (Federal Register 1996).

A lipophilic nonabsorbed substance in the GI tract can interfere with the absorption of lipophilic nutrients (Jandacek 1982). Several studies in animals and humans have shown that olestra interferes with the absorption of highly lipophilic nutrients. Serum concentrations of -tocopherol and 25-hydroxyergocalciferol, that component of serum total 25-hydroxyvitamin D which comes from the diet, and liver concentrations of retinol were reduced in pigs fed olestra (Cooper et al. 1996a and 1996b). Human studies showed that olestra reduced serum concentrations of -tocopherol, 25-hydroxyvitamin D, carotenoids and phylloquinone (Jones et al. 1991b, Koonsvitsky et al. 1997, Schlagheck et al. 1997a and 1997b). Sensitive functional assays revealed that vitamin K status was not affected by olestra (Koonsvitsky et al. 1997, Jones et al. 1991a, Schlagheck et al. 1997a and 1997b). In a study conducted in the same subjects used in the present study, 32 g of olestra, eaten in a single meal, may have reduced the absorption of retinyl palmitate although the effect was not statistically significant (Daher et al. 1997).

Because triglycerides are lipophilic, it might be expected that the absorption of dietary fat would be affected by olestra. A previous fat-balance study, however, did not reveal an effect on dietary fat absorption when human subjects consumed up to 50 g olestra/d for 10 d (Fallat et al. 1976). The investigators found no significant difference in the amount of dietary nonolestra fat excreted in the feces during the 10-d period in which olestra was eaten, compared with the amount excreted during a 10-d base-line period. Dietary olestra levels as high as 10% did not affect growth or feed efficiency in long-term animal studies (Lafranconi et al. 1994, Miller et al. 1991, Wood et al. 1991). These results provide evidence that olestra did not affect the absorption or utilization of the dietary macronutrients, including fat.

In this study, the effect of olestra on triglyceride absorption was measured by a dual-isotope technique, following the method of Thorsgaard Pedersen (1983). The technique employs ¹⁴C-triolein as a tracer of dietary fat and ⁵¹CrCl₃ as a nonabsorbed marker of gastrointestinal transit. The suitability of ¹⁴C-triolein as a tracer of dietary fat and of ⁵¹CrCl₃ as a nonabsorbed marker has been demonstrated in normal subjects and in patients with a wide variety of malabsorptive conditions and intestinal diseases (Jorgensen et al. 1991, Thorsgaard Pedersen 1984, Thorsgaard Pedersen and Halgreen 1985, Thorsgaard Pedersen et al. 1987).

The two radioisotopes are dosed simultaneously, and the efficiency of fat absorption is determined by measuring the excretion of ¹⁴C and ⁵¹Cr in the feces. The absorption is calculated from the quotient of the ratios of the fecal levels of the two isotopes, each expressed as a fraction of the amount of isotope dosed.

The dual-isotope method is more sensitive than the conventional fat-balance technique because it is not influenced by metabolic fat, that fat derived from colonic bacteria and intestinal secretions and sloughing. In addition, there is no need to collect feces quantitatively, to separate triglycerides or fatty acids from the feces, or to accurately control and measure total dietary fat intake.

The purpose of this study was to determine the absorption of triglyceride (¹⁴C-triolein) from a single meal containing 8, 20 or 32 g of olestra and to compare it with the absorption from a meal containing no olestra.

SUBJECTS AND METHODS

The subjects underwent a 30-d acclimation period to allow for any potential adaptation of GI functions to olestra consumption. During this period, the subjects consumed their habitual diets with the addition of olestra potato chips, which delivered 10 g olestra/d, or ordinary potato chips, which delivered an equivalent daily amount of triglyceride (placebo). After the adaptation period, the subjects were housed in a metabolic ward for 14 d. During this period, the subjects were given either 0, 8, 20 or 32 g olestra/d in potato chips and cookies. The daily dose was divided evenly among the three meals. On the day when the fat absorption study began, the entire daily dose of olestra was delivered in the breakfast along with the radioisotopes.

Assignments to treatment groups were made at the start of the adaptation period so that those subjects who received olestra potato chips would receive olestra during the metabolic ward period, and those who received placebo chips would receive placebo chips during the metabolic ward period.

During the 14 d when the subjects were in the metabolic ward, vitamin A absorption and fat absorption were measured in two sequential tests. The results of the vitamin A absorption study are presented in a separate paper (Daher et al. 1997).

The study was conducted in compliance with Good Clinical Practices regulations. Signed informed consent was obtained from each subject before enrollment. The protocol was approved by the Nebraska State Radiation Safety Committee and by the Institutional Review Board of Harris Laboratories (Lincoln, NE) where the study was conducted.

A four-subject pilot study was conducted prior to the main study to develop procedures for delivering controlled doses of the radioisotopes in food forms representing dietary fat consumption and to verify fecal collection and processing methods.

Exclusion criteria included a 48-h fecal fat excretion >15 g, diagnosed fat malabsorption secondary to any cause, history of GI disorders, exposure to radioactivity or X-rays within the past year, restriction of diet, and greater than average caloric need because of high activity level. Seventy-one subjects were enrolled in the study. Table 1 provides randomization parameters for the subject population at the beginning of the study.

Table 1. Randomization parameters for subjects completing the study [View Table]

The overall diet provided about 30% of energy as fat, about 55% as carbohydrate and about 15% as protein. The saturated:monounsaturated:polyunsaturated ratio of the fat was targeted at 1:1:1. Total digestible fat was kept constant across treatment groups by adding triglyceride to the diet, in the form of butter or corn oil margarine, to compensate for the amount of triglyceride replaced by olestra in the olestra potato chips. During the time the subjects were housed in the metabolic ward, they were required to eat at least 85% of all meals and to consume at least 90% of the test food.

On the day the radiomarkers were administered, the subjects ate only breakfast and dinner. They were required to eat all of the meals and 100% of the test foods. The breakfast consisted of a biscuit or a bagel, or some of each; jelly (28 g); apple juice (168 g); one half of a plain cake doughnut hole (the section of doughnut removed when the hole is cut), used to deliver the radiomarkers; potato chips, used to deliver the olestra; and instant tea (168 g). The amounts of biscuit and bagel were varied across the groups to keep fat, protein and carbohydrate levels constant. The bagels were essentially fat-free. The biscuits contained butter and corn oil margarine, which were used to keep digestible fat intake constant across all groups. The placebo group did not receive a biscuit and the 32-g olestra group did not receive a bagel. This breakfast provided about 4.72 MJ (1129 kcal) of energy and about 38 g of triglyceride, primarily corn oil, and contained the entire daily dose of olestra or placebo. Lunch consisted of a diet soft drink. Dinner consisted of an Italian sausage (105 g) on a white bun with mustard, French fries (1 cup), a bagel (144 g) with jelly (28 g), and instant tea (237 g). This meal provided about 5.99 MJ (1433 kcal) of energy and about 45 g of fat.

The total daily food consumption was controlled and determined by dispensing equal amounts of preweighed food to each subject and reweighing any uneaten portions. Daily intakes of total energy, fat, carbohydrate and protein (in percentage of energy and in grams) were calculated by the University of Minnesota Nutrient Data System, Version 2.3. Olestra intake was calculated from the amount of olestra potato chips consumed and from the analytically determined olestra content of the chips.

The nonabsorbable marker ⁵¹CrCl₃ (99.0% purity) was obtained from DuPont (Wilmington, DE). Because of its relatively short half-life, three separate batches of ⁵¹CrCl₃ with specific activities of 18.7, 17.2 and 14.3 Gbq/mg, respectively, were used for the three cohorts.

Sufficient volumes of the peanut oil solution of ¹⁴C-triolein and a sterile water solution of ⁵¹CrCl₃ to supply about 0.37 MBq of ¹⁴C-triolein and about 0.74 MBq of ⁵¹CrCl₃ were added to the freshly cut surface of one half of a doughnut hole. The one-half doughnut hole was eaten with the breakfast described above and 0, 8, 20 or 32 g of olestra, delivered in potato chips. The subjects were required to consume the entire meal and the entire supply of potato chips. They were not allowed to eat again until 12 h after the breakfast; this subsequent meal did not include olestra. Table 2 shows the mean amount of olestra in the breakfast and the dose of ¹⁴C-triolein for each treatment group.

Table 2. Mean amounts of olestra and 14C-triolein and 51CrCl3 [View Table]

The effect of olestra on triglyceride absorption was determined by ANOVA analysis of group mean ¹⁴C fractional absorption values. When the hypothesis of equal group means was rejected, the protected least significant difference multiple-comparison procedure was used to identify differences among the groups (Carmer and Swanson 1973, Welsch 1977). Linear trend tests were also conducted using a single degree of freedom.

Because multiple days of data as well as duplicate samples for each day were taken for each subject, the variability among subjects, between days for a given subject, and between samples from a given day for a given subject was estimated. The estimates were made by using ANOVA to obtain mean squares and the method of moments to estimate the variance components (Milliken and Johnson 1984). All statistical tests were performed at the two-sided 0.05 significance level, using PC SAS® version 6.04 (SAS Institute, Cary, NC).

RESULTS

The treatment groups did not differ in nutrient intake during the period they spent in the metabolic ward. Total energy intake ranged from 10.89 to 11.56 MJ, with about 29% from fat, 58% from carbohydrate, and 13% from protein. The mean nutrient intake on the day when the radioisotopes were administered was essentially constant across the groups (Table 3).

Table 3. Mean nutrient intake by treatment group on the day 14C-triolein and 51CrCl3 were administered [View Table]

A slight but significant dose-related effect of olestra on triglyceride absorption was observed. Table 4 shows the group mean ¹⁴C-triolein absorption values. In the absence of olestra, 99.1% of the ¹⁴C-triolein was absorbed, whereas subjects who consumed 32 g olestra with the breakfast absorbed 97.9%. This difference was significant. The absorption values for the 8- and 20-g olestra groups were not significantly different from placebo.

Table 4. Fractional absorption of 14C-triolein by treatment group1 [View Table]

Data from each of the two days of stool collections (not shown) were analyzed separately. The results were the same; a slight but significant dose-response effect occurred on each day. Group mean absorption values calculated from the earliest stool collection tended to be 0.5-1% greater than values calculated from the second stool collection. Absorption values calculated for an individual from the two 24-h stool collections generally differed by 1% or less, at most by 4%. Calculation of the variance (²) by the methods of moments (Milliken and Johnson 1984) showed that the greatest variability was between subjects within a group (² = 1.0 × 10⁴). The variance between days for a subject was 3.9 × 10⁵; the variance between duplicate samples taken from the feces collected on a given day from a given subject was 3.8 × 10⁵.

The stool samples with the highest ⁵¹Cr content were most commonly those collected 48-72 h after dosing. No consistent differences were found among the treatment groups with respect to the recovery of ⁵¹Cr in the two samples with the highest ⁵¹Cr levels. In those collections, 52% (range = 33-84%) of the ⁵¹Cr dose was recovered from the placebo group, 63% (range = 33-87%) from the 8-g olestra group, 48% (range = 8-67%) from the 20-g olestra group, and 57% (range = 22-85%) from the 32-g olestra group.

DISCUSSION

Only the highest dose of olestra (32 g) caused a slight (1.2%) but significant reduction in triolein absorption. Thirty-two grams of olestra in a single meal is an exaggerated dose: if people ate 32 g of olestra in each meal, the daily intake would be 96 g, almost 14 times the estimated 95th-percentile chronic intake (6.9 g/d) of the population of savory snacks eaters, the intended use of olestra (Webb et al. 1997). The 1.2% decrease in fat absorption produced by this dose is less than the change in fat absorption produced by common diet components such as calcium and fiber (Denke et al. 1993, Kay and Truswell 1977).

For the most nutritionally important components of dietary fat, the essential fatty acids (linoleic and -linolenic), the effect of olestra is likely to be less than the effect on triolein because the efficiency of digestion and absorption of triglycerides increases as the melting point decreases (Deuel 1955). Triolein has a melting point of 32°C, while trilinolein has a melting point of 43°C (Deuel 1951). Although neither triolein or trilinolein occurs widely in the diet, they are reasonable models for common vegetable oils such as olive oil, which is high in oleic acid, and safflower oil, which is high in linoleic acid. The absorption of dietary fats with melting points higher than that of triolein, such as those containing saturated fatty acids, may be affected more strongly by olestra than is the absorption of triolein. Yet, because these fats also are absorbed efficiently, one would not expect the effect to be substantially greater.

The maximum effect of olestra measured here on triglyceride absorption would not produce a nutritionally meaningful reduction in energy intake. For an individual consuming 8.37 MJ/d (2000 kcal) of energy from a diet that provides 30% of the energy from fat, or 67 g, the 1.2% reduction in absorption translates to a reduction in fat absorption of 0.8 g (67 × 0.012). This value represents a reduction in available energy of about 29 kJ (about 7 kcal).

In summary, olestra had a slight effect on fat absorption. Thirty-two grams of olestra reduced ¹⁴C-triolein absorption by 1.2%, a statistically significant but nutritionally nonsignificant change. Thirty-two grams of olestra exceeds by more than fourfold the estimated 90th-percentile chronic intake of olestra from savory snacks (6.9 g) by the total population. This amount is 25% greater than the estimated 90th-percentile single-day intake of olestra, 23.9 g, by the subgroup of heaviest eaters, 13- to 17-y-old adolescents (Webb et al. 1997).

ACKNOWLEDGMENTS