Effect of low carbohydrate diets during pregnancy on embryogenesis and fetal growth and development in rats

Effects in pregnant rats of feeding diets specifically deficient in carbohydrate were studied. The dietary nonprotein energy source was lipid, provided as intact fat (soybean oil) or a fatty acid mixture (edible oleic acid) or a combination of these. These diets provided 9.5% casein protein, which was shown to be minimally adequate in both the lipid-based experimental diets and the high carbohydrate control diet. The diets were fed from mating through d 21 of pregnancy, and pups were delivered by cesarean section. The soybean oil-based zero-carbohydrate diet supported embryogenesis and produced at term normal numbers of normal appearing pups of body weight lower than that of pups from the high carbohydrate control diet. In contrast, the oleic acid-based zero-carbohydrate diet failed to maintain pregnancy, indicating a requirement for carbohydrate or intact fat or both. To maintain pregnancy to term required both 5-10% intact fat and 4% carbohydrate as glucose or its equivalent amount of glycerol from lipid. From feeding graded levels of glucose in fatty acid based diets containing 5-10% intact fat as soybean oil, the carbohydrate requirement was found to be 6-8% glucose to sustain maternal food intake and weight gain and to produce normal fetal weight at term, and 12% glucose to provide approximately half the fetal liver glycogen levels in controls fed a high carbohydrate diet. These experiments have produced the first evidence of the quantitative requirement for carbohydrate for embryogenesis and fetal growth and development in the pregnant rat dam.