Studies evaluating the effects of high-carbohydrate and high-monounsaturated fat diets have yielded conflicting results, Dr. Abhimanyu Garg and colleagues note in their report, published in the November issue of Diabetes Care. They suggest that these studies may have been limited by their short duration.

Their own study compared the effect of two isocaloric diets: a high-carbohydrate diet consisting of 55% of energy as carbohydrate, 30% as fat, and 10% as monounsaturated fat; and a high-monounsaturated fat diet deriving 40% of calories from carbohydrate, 45% from fat, and 25% from monounsaturated fat.

The 42 patients with type 2 diabetes participating in the study consumed each diet for 6 weeks, with a median interval of 7 days between the two periods, with the order of the diets randomly assigned. Subjects were invited to continue the second diet for an additional 8 weeks (phase 2 extension). Eight patients continued on the high-monounsaturated fat diet and 13 continued on the high-carbohydrate diet.

Dr. Garg, from the University of Texas Southwestern Medical Center at Dallas, and his associates found that, after the initial 6-week periods, there were no significant differences between diets in systolic or diastolic blood pressure or heart rate.

However, after the 8 week-extension, the high carbohydrate diet was associated with diastolic blood pressure that was 7 mm Hg higher than at the end of both 6-week phases, systolic blood pressure was 6 mm Hg higher, and heart rate was higher by 7 to 8 beat per minute.

In contrast, the 8-week extension of the high-monounsaturated fat diet led to a significant lowering of heart rate compared with the end of the initial 6-week periods (6 to 7 bpm, p = 0.02 to 0.05). Systolic and diastolic blood pressure were 3 to 4 mm Hg lower after 14 weeks on the high-monounsaturated fat diet, but the difference did not reach statistical significance.