Effects of altering the ratio of dietary n-6 to n-3 fatty acids on insulin sensitivity, lipoprotein size, and postprandial lipemia in men and postmenopausal women aged 45-70 y: the OPTILIP Study.

BACKGROUND: Insulin resistance is associated with elevated plasma triacylglycerol, low HDL concentrations, elevated postprandial lipemia, and a predominance of small, dense LDLs (sdLDLs). It has been hypothesized that the dietary ratio of n-6 to n-3 (n-6:n-3) polyunsaturated fatty acids (PUFAs) may have favorable effects on these risk factors by increasing insulin sensitivity. OBJECTIVE: The objective was to measure changes in insulin sensitivity, lipoprotein size, and postprandial lipemia after a 6-mo alteration in n-6:n-3. DESIGN: In a randomized, parallel design in 258 subjects aged 45-70 y, we compared 4 diets providing 6% of energy as PUFAs with an n-6:n-3 between 5:1 and 3:1 with a control diet that had an n-6:n-3 of 10:1. The diets were enriched in alpha-linolenic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), or both. Insulin sensitivity was assessed with the homeostatic model assessment of insulin resistance and the revised quantitative insulin sensitivity test. RESULTS: Dietary intervention did not influence insulin sensitivity or postprandial lipase activities. Fasting and postprandial triacylglycerol concentrations were lower, and the proportion of sdLDLs decreased (by 12.7%; 95% CI: -22.9%, 2.4%), with an n-6:n-3 of approximately 3:1, which was achieved by the addition of long-chain n-3 PUFAs (EPA and DHA). CONCLUSIONS: Decreasing the n-6:n-3 does not influence insulin sensitivity or lipase activities in older subjects. The reduction in plasma triacylglycerol after an increased intake of n-3 long-chain PUFAs results in favorable changes in LDL size.

Effect of varying the ratio of n-6 to n-3 fatty acids by increasing the dietary intake of alpha-linolenic acid, eicosapentaenoic and docosahexaenoic acid, or both on fibrinogen and clotting factors VII and XII in persons aged 45-70 y: the OPTILIP study.

BACKGROUND: Elevated fibrinogen, activated factor XII (FXIIa), and factor VII coagulant activity (FVIIc) are associated with higher risk of fatal ischemic heart disease. This study tested the hypothesis that lowering the dietary ratio of n-6 to n-3 polyunsaturated fatty acids (n-6:n-3) would modify these risk factors in older men and women. OBJECTIVE: The objective of the study was to measure fasting hemostatic risk factors and postprandial changes in activated FVII (FVIIa) concentrations after a 6-mo alteration in dietary n-6:n-3. DESIGN: In a randomized, parallel design in 258 subjects aged 45-70 y, we compared 4 diets providing 6% of energy as polyunsaturated fatty acids at an n-6:n-3 between 5:1 and 3:1 with a control diet that had an n-6:n-3 of 10:1. The diets were enriched in alpha-linolenic acid, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid, or both. RESULTS: Fasting and 3-h plasma triacylglycerol concentrations were 11.1% and 7.2% lower with the diet that had an n-6:n-3 of approximately 3:1 and that was enriched with EPA and DHA than with the other diets. Fasting fibrinogen, FXIIa, FVIIc, FVIIa, and FVII antigen and postprandial FVIIa were not influenced by the diets. Avoiding foods high in fat the day before measurement decreased FVIIc and FVIIa by 8% and 19.2%, respectively. A test meal containing 50 g fat resulted in a mean 47% (95% CI: 42%, 52%) increase in FVIIa 6 h later, but the response did not differ by n-6:n-3. CONCLUSION: Decreasing the n-6:n-3 to approximately 3:1 by increasing the intake of EPA and DHA lowers fasting and postprandial plasma triacylglycerol concentrations in older persons but does not influence hemostatic risk factors.

The effect of guar galactomannan and water availability during hydrothermal processing on the hydrolysis of starch catalysed by pancreatic alpha-amylase.

The effects of water-soluble nonstarch polysaccharides (sNSP) on human metabolism are considered to be beneficial because they decrease postprandial glycaemia and insulinaemia following ingestion of starch-rich foods. The mechanisms by which sNSP attenuate the postprandial rise in blood glucose are not well understood but their presence increases the viscosity of gastrointestinal contents, which affects physiological functions, e.g. gastric emptying and peristalsis. Increased viscosity and decreased water activity during hydrothermal treatment of starch could influence alpha-amylase action. Using guar galactomannan as a representative of sNSP, we found that galactomannan has a direct noncompetitive inhibitory effect on alpha-amylase with a K(i) value of approximately 0.5% (3.3 microM). The inhibition is not time dependent and studies suggest direct binding of the enzyme to galactomannan; the resulting galactomannan-amylase complex being inactive. Processing of starch at low water levels greatly affects the catalytic efficiency of alpha-amylase. The Km value for starch heat treated in limited water is raised and kcat is lowered relative to starch gelatinised in excess water. Since galactomannan has no effect on the Km of alpha-amylase, we conclude that the inhibitory action of the polymer is not secondary to a decrease in available water. Neither does it seem to be a consequence of impaired diffusion of enzyme, substrate and products because of an increase in viscosity of the medium.Thus, the effects of sNSP in lowering postprandial glycaemia not only involve modifications of gut physiology, but also include direct inhibition of the first stage in the biochemical degradation of starch.