Growth and composition of brain myelin lipid in rats raised on restricted casein and soy protein diets

Studies were made in weanling and post-weanling rats to compare the effects of restricted dietary levels (8%) of casein (CS) and soy protein (SP) on the lipid composition of brain myelin, isolated by discontinuous sucrose density gradient ultracentrifugation. Diets containing normal levels (25%) of SP and CS (control), were also investigated. With the restricted protein diets, but not the 25% SP diet, there were significant reductions in the quantities of myelin, and of myelin lipid classes, relative to control. These deficits, including those of growth and body weight (but not brain weight), were greater at weaning than at 6 weeks of age. The severity of the deficits at each age, differed very significantly, depending on the type of dietary protein fed. Concerning the individual phospholipids at weaning, the restricted protein diets resulted in significantly lower values relative to control; these values were more depressed with the 8% SP than with 8% CS diet. The results were explained on the basis of a possible greater amino acid imbalance in the low protein SP diet than the corresponding CS diet.