Journal Name:
Ann. Nutr. Metab.
Article Title:
Effects of Dietary alpha-Linolenic Acid, Eicosapentaenoic Acid or Docosahexaenoic Acid on Parameters of Glucose Metabolism in Healthy Volunteers
Date Written:
2008
Volume:
53
Number:
NA
Page:
182
Author(s):
Egert, S.; Fobke, M.; Andersen, G.; Somoza, V.; Erbersdobler, H.F.; Wahrburg, U.
Article:
Recent attention has been focused on blood glucose concentrations because, depending on its concentrations in blood, glucose reacts with amino groups or plasma and tissue proteins to form glycosylated proteins. These glycosylated proteins gradually transform non-enzymatically into advanced glycosylation end products and have been shown to result in altered protein function of the affected molecules. Glycosylation of low-density lipoproteins, for example, was found to be associated with impaired receptor-mediated uptake and catabolism. Glucose concentrations also play an important role in the metabolic syndrome. A high blood glucose concentration indicates the beginning or the existence of glucose intolerance and insulin resistance, which may result in the manifestation of type 2 diabetes mellitus.
Glycosylated haemoglobin (HbA1c) is a biomarker of long-term glucose homeostasis that reflects blood glucose concentrations over the previous 6–10 weeks and is associated with cardiovascular and ischaemic heart disease mortality in non-diabetic subjects. HbA1c was found to be associated with dietary intake of fats, particularly saturated fats. Fructosamine, another non-enzymatic glycated substance in the blood, is a marker of glycaemia in the previous 2–3 weeks. Fructosamine, like HbA1c, is associated with cardiovascular disease in non-diabetic subjects.
The objective of this study was to investigate the effects of alpha -linolenic acid (ALA) and purified eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) on fasting concentrations of glucose, insulin, fructosamine, on glycosylated haemoglobin (HbA1c) and on insulin sensitivity. The clinical component consisted of a randomized strictly controlled dietary study in 48 healthy volunteers (13 males, 35 females) of normal body weight (mean age 25.9 years) with three dietary groups (ALA, EPA and DHA) and a parallel design, consisting of two consecutive periods. Subjects received a 2- week wash-in diet rich in monounsaturated fatty acids followed by experimental diets enriched with equal amounts of ALA, EPA, or DHA for 3 weeks. Mean dietary intake of ALA in the ALA group was 6.0 g/day (2.5% of energy intake), mean intake of EPA in the EPA group was 2.8 g/day (1.1% of energy intake) and mean intake of DHA in the DHA group was 2.9 g/day (1.1% of energy intake).
Fasting serum concentrations of insulin and fructosamine and of HbA1c did not change significantly after consuming the ALA, EPA or DHA diet. Fasting serum glucose levels did not change significantly following either the ALA or DHA diet. During the EPA diet, fasting glucose concentration slightly increased by 0.15 mmol/l. No effects on insulin sensitivity indicated by the HOMA insulin resistance index were observed.
Except for a minor effect of EPA on fasting glucose levels, the moderate amounts of dietary ALA, EPA or DHA administered in this study did not significantly affect blood concentrations of glucose, insulin, fructosamine and HbA1c in healthy normal-weight men and women over a time course of 3 weeks.
Higher intakes of EPA and DHA (about 4 g/day) have also been shown to increase fasting plasma glucose concentrations in mildly hyperlipidemic men and type- 2-diabetic patients. The experimental period of 3 weeks was not long enough to reflect diet-induced changes in HbA1c levels because of its long half-life, which depends on the half-life of erythrocytes, which is about 120 days. Oral diabetic medication, obesity or insulin resistance and other conditions such as hypertension may also have affected insulin sensitivity in this study.
Previous studies in healthy subjects also show that omega 3 PUFA could increase insulin sensitivity at least in the post-prandial state (oral glucose load). It is unclear whether ALA confers similar benefits as it has not been studied to the same extent as EPA and DHA.
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