In a randomized cross-over study 5 gestational diabetic women were tested on a low fat, high unrefined carbohydrate (HC) diet and a low carbohydrate (LC) diet for a period of 4 days each. Glucose tolerance was shown to be significantly improved on the HC diet compared to the LC diet (p less than 0.05). Urinary glucose output was 50% lower on the HC diet (1.3 +/- 1.1 mmol/d) than on the LC diet (2.6 +/- 3.0 mmol/d), although this difference was not statistically significant. Fasting free fatty acid levels were significantly lower on the HC diet (HC 590 +/- 270 mumol/l, LC 690 +/- 270 mumol/l; p less than 0.02); as were the fasting cholesterol levels (HC 5.9 +/- 1.1 mmol/l, LC 6.3 +/- 1.1 mmol/l; p less than 0.01). Fasting plasma glucose, 2 h postprandial plasma glucose, and fasting plasma triglyceride levels did not differ on the 2 diets. These pilot study results suggest that diets low in fat and high in unrefined carbohydrate content are beneficial to the management of women with gestational diabetes.