Intake of a Diet High in Trans Monounsaturated Fatty Acids or Saturated Fatty Acids: Effects on postprandial insulinemia and glycemia in obese patients with NIDDM

OBJECTIVE: High intake of trans fatty acids and saturated fatty acids (SFAs) is known to increase the risk of coronary heart disease. We studied the effects of diets enriched in various fatty acids on postprandial insulinemia and fasting serum levels of lipids and lipoproteins in obese patients with NIDDM. RESEARCH DESIGN AND METHODS: Sixteen obese NIDDM patients were studied in a free-living outpatient regimen. After a run-in period, the patients received three different isocaloric diets for 6 weeks using a randomized crossover design. The patients were instructed to keep the energy intake from carbohydrate and protein constant at 50 and 20 E% (percent of energy intake), respectively, on all three diets. The fat composition of the diets differed: saturated fat (SAT) diet (20 E% SFAs, 5 E% polyunsaturated fatty acids PUFAs, and 5 E% monounsaturated fatty acids MUFAs) versus cis monounsaturated fatty acid (CMUFA) diet (20 E% cis-MUFAs, 5 E% PUFAs, and 5 E% SFAs) versus trans monounsaturated fatty acid (TMUFA) diet (20 E% trans-MUFAs, 5 E% PUFAs, and 5 E% SFAs). Fasting serum levels of lipids and lipoproteins were measured at baseline and in the fasting state before meal tolerance tests at the end of each study period. Insulin secretion was assessed from incremental serum insulin and C-peptide responses during the meal tests. RESULTS: BMI, waist-to-hip ratio, and glycemic control remained stable throughout the study. After meal stimulation, postprandial glycemic responses were similar on all diets; however, serum insulin and C-peptide responses were greater following the TMUFA and SAT diets than following the baseline or CMUFA diets (P < 0.05). No statistical difference was found in fasting levels of serum lipids (total cholesterol, triglyceride, phospholipid, and nonesterified fatty acids) or lipoproteins of HDL cholesterol, VLDL cholesterol, LDL cholesterol, and apolipoprotein B between diets. CONCLUSIONS: In the presence of unchanged glycemia, both dietary trans fatty acids and SFAs induce an increase in postprandial insulinemia in obese patients with NIDDM.