Effects of methionine addition in soya bean or casein diets supplemented with carrageenan on weight gain and blood lipids in rats

Seven groups of 12 Wistar rats were fed during two experimental periods. During the first period of 4 weeks, rats were fed diets containing 100 g kg^?1 of casein or soya-protein. In the case of casein, diets contained casein, casein + 3.5 g kg^?1 of sodium carrageenan and casein + 3.5 g kg^?1 of sodium carrageenan + 1 g kg^?1 of DL-methionine. In the case of soya protein, diets contained soya protein, soya protein + 6.2 g kg^?1 of sodium carrageenan, soya protein + 6.2 g kg^?1 of sodium carrageenan + 1 g kg^?1 of DL-methionine and soya protein + 1 g kg^?1 of DL-methionine. During the second period of 8 weeks, all rats were fed laboratory pellets containing 170 g kg^?1 of standard protein mixture. Methionine supplementation of heated soya bean meal containing carrageenan prevented the decrease of growth observed with unsupplemented diet. Methionine supplementation of casein improved protein efficiency ratio and had no effect on long-term growth of rats because carrageenan did not cause growth retardation. At the end of second period, carrageenan ingested during the first period had no effect on plasma cholesterol. When carrageenans added to casein were ingested during the first period, plasma triglycerides were significantly lower after the second period. It would seem that carrageenans induce protein malnutrition by a lack of methionine when they are present in low protein diets with low methionine content, and that a sufficient content of methionine in diets prevents the carrageenan effect.