Effects of pregnancy, sucrose, and various low-protein diets on the eating behavior of rats.

To assess the effects of various low-protein diets on the eating behavior of female rats, 280 rats were assigned to one of 20 groups, according to a 5 x 2 x 2 (Protein Level x Pregnancy x Sugar) design. Each rat was offered one of five isocaloric, soy-based diets: 25%, 8%, 4%, 2% or 1% protein diet. The subjects' intakes and weights were recorded daily for 3 weeks. Protein content of the diet, pregnancy, and the presence of dietary sucrose all had significant effects on diet, sucrose, and protein intake. By the third week of the experiment, pregnant rats offered 1%, 2% or 4% protein diets consumed significantly less of their diet than did their nonpregnant controls, whereas pregnant rats in the 25% protein group consumed significantly more of their diet than did nonpregnant controls. The eating behavior of the rats offered the 8% protein diet was most affected by the presence of dietary sucrose. Pregnant rats in the 8% protein group consumed less of their diet than did nonpregnant controls when sucrose was also offered, but they consumed more of their diet than did nonpregnant controls when sucrose was not offered. A learned food aversion is probably the best explanation for the severe reduction of diet intake observed in pregnant rats in all of the 1%, 2%, and 4% protein groups, as well as in pregnant rats offered the 8% protein diet and sucrose.