1. Each of nine volunteers was fed three different diets. The percentage of total daily energy provided by fat, carbohydrate and protein remained constant, but the nature of the fat and carbohydrate was altered. The first diet contained ordinary amounts of sucrose and predominantly saturated fat. During the second dietary period, fat remained saturated, but the quantity of sucrose was increased at the expense of complex carbohydrate. In the third dietary period, the sucrose intake remained high, but fat was supplied chiefly in the polyunsaturated form.
2. A small but statistically significant increase of serum fasting cholesterol and triglyceride was observed during the second dietary period, but on the third diet levels of both lipids fell to concentrations not significantly different from those seen on the first diet.