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.