Poor Digestibility of Fully Hydrogenated Soybean Oil in Rats: A Potential Benefit of Hydrogenated Fats and Oils

Manuscript received 27 March 1997. Initial reviews completed 9 June 1997. Revision accepted 8 January 1998.

Randall J. Kaplan^*, and Carol E. Greenwood^{*, ,}

^* Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 3E2, Canada and  Kunin-Lunenfeld Clinical Research Unit, Baycrest Centre for Geriatric Care, Toronto, Ontario M6A 2E1, Canada

The digestibility and absorption of dietary triacylglycerols are dependent on a number of factors including their fatty acid profile. Data demonstrating poor bioavailability of dietary stearic acid would suggest that hydrogenated oil sources would have lower digestibility coefficients compared with their native oils. To test this hypothesis, postweanling rats were fed one of four diets, formulated to contain 40% of energy as fat (assuming complete bioavailability), for 14 d. The diets only differed by fat type, containing soybean oil (SBO), fully hydrogenated soybean oil (HSB), medium-chain triglyceride oil (MCT), or hydrogenated coconut oil (HCO). Rats fed HSB consumed more food during the last 6 d (155.2 ± 2.7 g) than those in each of the other groups (MCT: 118.9 ± 2.2 g; HCO: 124.7 ± 3.2 g; SBO: 123.8 ± 2.3 g), yet, they did not gain more weight. Two-day fecal excretion was almost three times greater in HSB-fed rats than in rats fed any other diet (P < 0.0001) because HSB was very poorly available. The digestibility coefficients (a measure of bioavailability) of the four fats were: HSB (30.9 ± 1.3%) < HCO (94.5 ± 0.4%) < SBO (97.0 ± 0.4%) < MCT (98.7 ± 0.2%) (P < 0.0007). All rats compensated for the incomplete availability of the fats, as apparent absorbable energy consumed did not differ among diet groups. The present data suggest that HSB only contributes 11.6 kJ/g (most fats contribute ~37.7 kJ/g) and that not only manufactured fat substitutes, such as olestra, but also more conventional fats are incompletely available to the body. Foods that currently contain HSB may contribute much less utilizable fat and energy than presently realized.

The Journal of Nutrition Vol. 128 No. 5 May 1998, pp. 875-880
Copyright ©1998 by the American Society for Nutritional Sciences

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