Type 2 (insulin independent) diabetic women were randomly allocated to receive advice for low fat diets or low carbohydrate diets. By 24 h weighted dietary intakes before and after a mean interval of six months, patients in the low fat group had reduced their fat intake from 41% to 31% of total energy, while carbohydrate percentage of total energy intake increased from 38% to 46%. Percentage energy intake from fat and carbohydrate in the control group remained unchanged. Body weight fell in both groups especially for patients in the low fat group who were obese (weight/height2 greater than or equal to 28 kg/m2). Mean plasma glucose, HbA1, and triglycerides were unchanged. Mean plasma total cholesterol fell significantly in the low fat group compared with the controls (p less than 0.001), but there was no significant difference in the small reduction of high density lipoprotein cholesterol observed in both groups. Thus, adherence to low fat diets occurred without deterioration of diabetes and with benefit for weight and total cholesterol.