Compounds other than threonine that affect fat deposition in the livers of rats fed low protein diets.

The level of fat in the livers of young rats fed a 9 per cent casein-sucrose diet containing choline and the other known lipotropic agents is markedly decreased when additional threonine (0.18 to 0.36 per cent) is included in the diet (1, 2). Harper et al. (3) also found that the deposition of liver fat was reduced when the low protein diet was supplemented with a high level (1 to 1.5 per cent) of glycine, serine, glycocyamine, betaine, or choline. The larger amounts of the latter compounds, however, were less effective than threonine. They also noted that glycine, choline, and betaine further reduced the level of liver fat in rats fed 9 per cent casein diets that contained additional threonine and that combinations of 1.5 per cent glycine with betaine, serine, or choline caused greater reductions than did 1.5 per cent glycine alone. The level of fat in the livers of animals fed a diet containing 2 per cent glytine was lower than that of a group receiving only 1.5 per cent glycine. A mixture of ketogenic amino acids (1 per cent nn-leucine, 1 per cent DLisoleucine, and 1 per cent L-tyrosine) was also found to reduce deposition of liver fat. Since the level of choline in the diet was already adequate and since liver fat deposition was not increased when the methionine normally added to the diet was replaced with cystine, it was assumed that neither choline nor the other supplements caused reductions in the level of liver fat by relieving a classical choline deficiency. The work reported here was undertaken in order to investigate further the effects of glycine and a number of related compounds on the deposition of fat in the livers of rats fed 9 per cent casein-sucrose diets.