Journal Name:
Diabetologia
Article Title:
Acute effects of monounsaturated fatty acids with and without omega-3 fatty acids on vascular reactivity in individuals with type 2 diabetes
Date Written:
2005
Volume:
48
Number:
0
Page:
113
Author(s):
West, S.G.; Hecker, K.D.; Mustad , V.A.; Nicholson, S.; Schoemer, S.L.; Wagner , P.; Hinderliter, A.L.; Ulbrecht, J.; Ruey, P.; Kris-Etherton, P.M.
Article:
Vascular endothelium dysfunction is an important initial step in the development of atherosclerosis. Endothelial function is impaired in individuals with type 2 diabetes. Increased consumption of long-chain omega-3 fatty acids is associated with reduced risk of cardiovascular disease in type 2 diabetes, and placebo-controlled studies suggests that improvements in endothelial function may be a mechanism for this effect . The objective of this study was a comparison of the vascular and metabolic effects of fatty acid blends containing plant-derived and marine-derived n-3 fatty acids in adults with type 2 diabetes, and whether inclusion in a meal alters the postprandial effects of oleic acid.
In this study, the acute post¬prandial effects of meals containing unsaturated fatty acids on flow-mediated dilation (FMD) of the brachial artery and triacylglycerols in individuals with type 2 diabetes was assessed. It was hypothesized that the consumption of omega-3 fatty acids would enhance vascular function. Saturated fat reduces FMD for several hours, but there is inconsistent evidence about whether foods containing unsaturated fats impair FMD acutely. Little is known about the acute effects of omega-3 fatty acids on vascular reactivity.
FMD was measured before and 4 h after 3 test meals (50 g fat, 2,615 kJ) in 18 healthy adults with type 2 diabetes. The monounsaturated fatty acids (MUFA) meal contained 50 g fat from high oleic safflower and canola oils. Two addi¬tional meals were prepared by replacing 7% to 8% of MUFA with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) from sardine oil or α-linolenic acid (ALA) from canola oil.
In the sample as a whole, FMD was increased 17% at 4 h vs. the fasting baseline. After the MUFA meal, subjects with the largest increases in triacylglycerols had the largest FMD decreases. The opposite pattern was observed after meals containing DHA, EPA or ALA. In subjects with high fasting triacylglycerols, meals containing 3 to 5 g of omega-¬3 fatty acids increased FMD by 50% to 80% and MUFA alone had no significant effects on FMD. In this study, FMD was not impaired 4 h after a high-fat meal containing predominantly unsaturated fatty acids. In fact, when the sample as a whole was considered, FMD significantly increased at 4 h. However, fasting triacylglycerols status, triacylglycerols response to the meals, and the fatty acid profile of the meals were important determinants of the direction and magnitude of postprandial responses. Subjects with elevated triacylgly¬cerols concentrations showed significant FMD impairment under fasting conditions, slower clearance of glucose following a meal, and larger triacylglycerols increases after a meal containing 50 g of the MUFA fat blend when compared to the low triacylglycerols group. Importantly, however, when 7% to 8% of the MUFA fat blend was replaced with n-3 fatty acids from canola or sardine oil, the high triacylglycerols group exhibited significant increases in FMD and smaller increases in postprandial triacylgly¬cerols concentrations.
Assessment of FMD is not currently recommended as a clinical marker of cardiovascular disease risk, in part because small variations in technique have large effects on FMD estimates. The authors of this study suggest that triacylglycerols sta¬tus be used to identify patients who may benefit from n-3 fatty acids. The data suggest that marine and plant-derived n-3 fatty acids would be equally effective. It is also important to consider the meaning of these effects in the context of recommended dietary intakes of n-3 fatty acids. Americans typically consume ∼1.6 g/d of n-3 fatty acids from plant and marine sources combined and vegetable oils are the primary source. In this study, 3.5 g of ALA and 4.8 g of EPA+DHA as part of a 50 g fat load was provided. The National Academies recommend that a nutritionally adequate intake of ALA is 0.8–1.1 g/day, and 10% of this amount may be supplied as EPA and DHA.
In summary, the present study showed that a meal containing 50 g of fat, primarily from unsaturated fatty acids, was not associated with impaired endothelial function. In patients with type 2 diabetes and high fasting triacylglycerols levels, meals containing 3 to 5 g of either plant or marine-derived n-3 fatty acids actually signifi¬cantly improved postprandial lipaemia and endothelial function. The data support the view that the vascular effects of a meal are dependent on both the fatty acid composition of the meal, and the metabolic status of the subject. From a clinical perspective, the results suggest that adjunctive treatment with n-3 fatty acids could enhance endothelial function even in patients who are already taking hypoglycaemic drugs. Future studies should assess whether the apparent vascular benefits of n-3 and oleic fatty acids from canola oil are observed after long-term administration, and test whether changes in markers of oxidative stress, serum fatty acids, and L-arginine and nitric oxide metabolism are potential mechanisms for these effects.
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