The first approach to treatment of dyslipidaemia is with diet. Currently, modified soybean protein is often included in the diet. A study was made of 32 patients with types IIa and IIb dyslipidaemia to see what changes in blood lipids could be induced by a simple low fat diet and a diet with modified soybean protein substituted for part of the animal protein. After six weeks on the initial low fat diet, all of the patients had lower total cholesterol and triglyceride levels, but there were no significant changes in the high density lipoprotein-cholesterol levels. The same diet was continued for eight weeks by 19 of the patients, who continued to improve. The 13 patients who had shown the least response to the initial simple low protein diet were given a diet in which the animal protein was partially replaced with modified soybean protein. This diet further decreased the total cholesterol.