Insulin sensitivity after a reduced-fat diet and a monoene-enriched diet in subjects with elevated serum cholesterol and triglyceride concentrations.

BACKGROUND AND AIMS: To investigate the effect of a reduced-fat diet and a monoene-enriched diet (MUFA diet) on serum lipids, glucose and insulin metabolism in subjects with elevated cholesterol and triglyceride concentrations. METHODS AND RESULTS: Eighteen subjects with elevated serum cholesterol and triglyceride concentrations consumed the MUFA diet (39% of energy (E%) as fat and 21 E% monoenes) and the reduced-fat diet (34 E% fat, 16 E% monoenes) for 4 weeks according to a randomized cross-over design. Both periods were preceded by consumption of a standardized baseline diet for 2 weeks. Serum lipid and lipoprotein concentrations were determined at the beginning and end of each diet period. A frequently sampled intravenous glucose tolerance test was performed after the MUFA diet and the reduced-fat diet. Insulin sensitivity index (SI) was 40% higher after the reduced-fat diet than after the MUFA diet (2.42 +/- 0.42 vs 1.73 +/- 0.24 10(-4) min-1 U-1 ml-1, p = 0.018). This change in insulin sensitivity was seen in 13 subjects and was most evident in those who began with the MUFA diet. Compared to the baseline diet (high in saturated fat), both experimental diets lowered serum total and LDL cholesterol concentrations (6.6-6.9%, p < 0.05 and 7.4-8.0%, p < 0.05 respectively). CONCLUSIONS: Both diets were equally effective in lowering serum lipid concentrations, but the reduced-fat diet resulted in better insulin sensitivity.

A high-trans fatty acid diet and insulin sensitivity in young healthy women.

Epidemiological and experimental studies suggest that a diet rich in saturated fat affects insulin sensitivity. Monoenes and dienes that have an usaturated bond with the trans configuration (trans fatty acids) resemble saturated fatty acids with respect to structure, but no published data are available on the effect of trans fatty acids on insulin sensitivity. Therefore, the effects of diets high in trans fatty acids (TFA diet) and oleic acid (monounsaturated fat [MUFA] diet) on glucose and lipid metabolism were studied in 14 healthy women. Subjects consumed both experimental diets for 4 weeks according to a randomized crossover study design. Both experimental diet periods were preceded by consumption of a standardized baseline diet for 2 weeks. The diets provided 36.6% to 37.9% of energy (E%) as fat. In the TFA diet, there was 5.1 E% trans fatty acids, and in the MUFA diet, 5.2 E% oleic acid, substituted for saturated fatty acids in the baseline diet. A frequently sampled intravenous glucose tolerance test (FSIGT) was performed at the end of the experimental diet periods. Glucose effectiveness (S(G)) and the insulin sensitivity index (S(I)) did not differ after the two experimental diet periods. There was also no difference in the acute insulin response between the diets. The total cholesterol to high-density lipoprotein (HDL) cholesterol ratio and serum total triglyceride, HDL, and low-density lipoprotein (LDL) triglyceride and apolipoprotein B (apoB) concentrations were higher (P < .05) after the TFA diet. In conclusion, in young healthy women, the TFA diet resulted in a higher total/HDL cholesterol ratio and an elevation in triglyceride and apo B concentrations but had no effect on glucose and insulin metabolism compared with the MUFA diet.

Divergent incorporation of dietary trans fatty acids in different serum lipid fractions.

Trans fatty acids may be involved in atherosclerotic vascular diseases. We investigated the incorporation of dietary trans fatty acids and oleic acid into the serum triglycerides (TG), cholesterol esters (CE), and phospholipids (PL). Fourteen healthy female volunteers, aged 23.2+/-3.1 yr (mean+/-SD), body mass index 20.8+/-2.1 kg/m2 participated in this study. All subjects consumed both a trans fatty acid-enriched diet (TRANS diet) and an oleic acid-enriched diet (OLEIC diet) for 4 wk according to a randomized crossover design. Both experimental diet periods were preceded by consumption of a baseline diet for 2 wk which supplied 37% of total energy (E%) as fat: 18 E% from saturated fatty acids (SFA), 12 E% from monounsaturated fatty acids, and 6 E% from polyunsaturated fatty acids. Five E% of the SFA in the baseline diet was replaced by trans fatty acids (18:1t and 18:2c,t + 18:2t,t, where c is cis and t is trans) in the TRANS diet and by oleic acid (18:1n-9) in the OLEIC diet. After the TRANS diet, the proportions of 18:1t and 18:2t increased (P<0.001) in all serum lipid fractions analyzed. The increase of 18:1t in TG and PL (1.80+/-0.28 vs. 5.26+/-1.40; 1.07+/-0.34 vs. 3.39+/-0.76 mol% of total fatty acids, respectively) was markedly higher than that in CE (0.44+/-0.07 vs. 0.92+/-0.26), whereas that of 18:2t was nearly the same in all three fractions. The proportions of palmitic, stearic, arachidonic, and eicosapentaenoic acids in TG, CE, and PL and that of oleic acid in TG and CE were decreased when compared with the baseline value. In contrast, the proportion of palmitoleic acid in TG and PL and that of linoleic acid in PL increased on the TRANS diet. After consumption of the OLEIC diet, the proportion of oleic acid increased in all three lipid fractions analyzed, and the percentage increase was nearly the same in all fractions. In contrast, the proportions of 18:1t in TG and PL and 18:2t in TG and CE decreased when compared with the baseline value. In conclusion, a moderate increase in dietary trans fatty acids resulted in a marked incorporation into serum lipids and decreased the conversion of linoleic acid to its more unsaturated long-chain metabolites. Analysis of 18:1t from serum TG and PL seems to reflect reliably the dietary intake of this fatty acid.

A high-stearic acid diet does not impair glucose tolerance and insulin sensitivity in healthy women.

Results in epidemiological and experimental studies suggest that a diet rich in saturated fat may affect insulin sensitivity. However, no published data are available on the effect of stearic acid in this respect. Therefore, we examined the effects of a high-stearic acid diet and a high-oleic acid diet on glucose metabolism, serum lipids and lipoproteins, and blood coagulation factors in 15 healthy female subjects. Subjects followed the two experimental diets for 4 weeks according to a randomized crossover design. Both experimental diet periods were preceded by consumption of a baseline diet for 2 weeks. The diets provided 36% of energy (E%) as fat. In the experimental diets, 5 E% stearic or oleic acid was substituted for 5 E% of saturated fatty acids in the baseline diet. After the experimental diets, no differences were found in the insulin sensitivity index (mean+/-SEM, 5.4+/-1.9 v 5.2+/-1.6 x 10(-4) min(-1) x microU(-1) x mL(-1), nonsignificant [NS]), glucose effectiveness (0.026+/-0.006 v 0.026+/-0.003 min(-1), NS), or first-phase insulin reaction ([FPIR] 368+/-57 v 374+/-66 mU/L x min, NS). The concentration of serum lipids and lipoproteins and blood coagulation factors did not differ after the diet periods. In conclusion, a diet rich in stearic acid did not deteriorate glucose tolerance or insulin action in young healthy female subjects as compared with a diet rich in oleic acid.

Serum leptin in subjects with impaired glucose tolerance in relation to insulin sensitivity and first-phase insulin response.

OBJECTIVE: It has been suggested that insulin could regulate the secretion of leptin, the ob gene product, but the findings have been contradictory. Therefore, we studied the association between leptin and insulin secretion and insulin sensitivity in impaired glucose tolerance (IGT). SUBJECTS: 39 obese subjects (17 men, 22 women, body mass index (BMI) 30.6 +/- 0.6 kg/m2, age 54 +/- 1 y, mean +/- s.e.m.) with IGT. MEASUREMENTS: Leptin, insulin sensitivity and first-phase insulin response (frequently sampled intravenous glucose tolerance test), anthropometry, infrared densitometric assay. RESULTS: Leptin correlated with BMI (r = 0.36, P = 0.022), fat percent (r = 0.74, P < 0.001) and fat mass (r = 0.53, P < 0.001). After adjustment for sex and fat mass, leptin showed no significant linear correlation with fasting insulin, insulin sensitivity or first-phase insulin response. CONCLUSION: In obese IGT subjects fat mass is the main correlate of serum leptin concentration. First-phase insulin response or the degree of insulin resistance are not associated with leptin in IGT.

Linoleic acid intake and susceptibility of very-low-density and low density lipoproteins to oxidation in men.

Lipoprotein peroxidation is thought to play an important role in atherogenesis. In the Kuopio Atherosclerosis Prevention Study (KAPS) the intake of fat and fatty acids, the oxidation susceptibility of the plasma very-low-density + low-density lipoprotein (VLDL+LDL) fraction (by induction with copper or hemin and hydrogen peroxide), and concentrations of plasma antioxidants, serum lipids, and lipoproteins were measured in 393 men. In the multivariate-regression model dietary linoleic acid was the most important determinant of the maximal oxidation velocity for the hemin assay (standardized regression coefficient = 0.294, P<0.0001). In the copper assay the association of dietary linoleic acid and maximal oxidation velocity was second in order of strength (standardized regression coefficient = 0.324, P< 0.0001). We conclude that high linoleic acid intake is associated with increased oxidation susceptibility of atherogenic lipoproteins in men.