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Nutritional Studies on Rats on Diets Containing High Levels of Partial Ester Emulsifiers¹

I. General Plan and Procedures; Growth and Food Utilization

Food Research Laboratories, Inc. Long Island City, New York

The plan of a chronic feeding study is described in which rats were maintained for two years on nutritionally adequate diets composed principally of natural ingredients, supplemented with 0, 5, 10 and 20% levels of partial ester emulsifiers or of hydrogenated vegetable oil. The emulsifiers were Myrj 45, Myrj 52, Span 60, Tween 60, Tween 65, Tween 80 and a mixture thereof. The parent generation consisted of 810 rats. Three successive generations comprising 1440 additional rats were likewise observed for growth, food efficiency and reproductive performance.

Observations were made of body weight and food consumption permitting estimates of the efficiency of food utilization; hemocytology and hemochemistry ; physical appearance and behavior; water consumption; laxation; metabolic utilization of the partial esters; reproduction and lactation mortality rates; and gross and microscopic pathology. The findings and conclusions are to be reported in a series of papers of which this is the first.

The growth responses of the emulsifier groups at the 5 or 10% levels were not significantly different from the controls. The only emulsifier group at these levels showing a significantly lower gain than the corresponding Primex group were the males on 5% Tween 80. At the 20% level the males (but not the females) in all emulsifier groups except Myrj 45 showed a moderate but statistically significant reduction in weight gain as compared with the controls; the 20% Primex group gained even more than the controls.

Since food consumption records were maintained for the first 12 weeks of the test and the growth curves plotted on a log weight: reciprocal age basis were essentially linear, extensive statistical analyses were made for this initial period. The data reveal a trend in the direction of higher food intake with increasing emulsifier level whereas the opposite was noted in the Primex groups whose diets, in contrast with the emulsifier diets, increased substantially in caloric density as the fat level increased. Regardless of the test supplement fed, the efficiency of food utilization (EFU) as well as the efficiency of caloric utilization (ECU) were somewhat higher in the initial (F₀) generation than in the succeeding generations. This may be explained by the difference in nutritional reserves at weaning between the first generation and all the descendent generations.

Analyses of the data for efficiency of utilization of the diets after adjustment to an isocaloric basis showed no statistically significant (p = 0.05) difference either among the groups receiving the various emulsifiers or between them and the basal control group with one exception, namely a small but significant diminution in efficiency of the diet containing 20% Tween 60.

Manuscript received 9 March 1956.