Objective and subjects: The effects of a high-fat, monounsaturated-fat enriched (Mono) diet and a reduced-fat, polyunsaturated-fat enriched (Poly) diet on lipid and glucose metabolism were compared in 31 subjects with impaired glucose tolerance.
Design and interventions: After 3 weeks on a Run-in diet (37; 18:11:5, indicating energy percentages from total fat; saturated:monounsaturated:polyunsaturated fatty acids in the actual diets) subjects were randomized into a Poly-diet (34; 11:10:10) or a Mono-diet (40; 11:19:8) for 8 weeks.
Results: In the Mono group fasting plasma glucose (mean +/- SD) was lower after the test diet than after the run-in period (6.4 +/- 1.3 vs 6.0 +/- 0.8 mmol/L, 0 vs 8 weeks, P = 0.008), but remained unchanged in the Poly group (6.2 +/- 0.6 vs 6.1 +/- 0.7 mmol/L). Glucose effectiveness (SG), insulin sensitivity index and the first phase insulin response in an intravenous glucose tolerance test did not change significantly during either of the diets, but at the end of the study SG was higher in the Mono group than in the Poly group (P = 0.013). Serum total cholesterol, LDL cholesterol, and apolipoprotein B decreased in the Mono group, while in the Poly group only serum total cholesterol decreased significantly. However, the mean changes in serum lipids and lipoproteins did not differ significantly between the groups.
Conclusions: In free-living subjects with impaired glucose tolerance both the Mono-diet and the Poly-diet consumed after a saturated-fat enriched Run-in diet improved serum lipid profile and the Mono-diet seemed to improve glucose metabolism as well.