Journal Name:
Diabetologia
Article Title:
Substituting dietary saturated for monounsaturated fat impairs insulin sensitivity in healthy men and women: the KANWU Study.
Date Written:
2001
Volume:
44
Number:
n/a
Page:
312
Author(s):
Vessby, B.; Unsitupa, M.; Hermansen, K.; Riccard, G.; Rivellese, A.A.; Tapsell, L.C.; Nälsén, C.; Berglund, L.; Louheranta, A.; Rasmussen, B.M.; Calvert, G.D.; Maffetone, A; Perdersen, E.; Gustafsson, I.-B.; Storlien, L.H.
Article:
The amount and quality of fat in the diet could be important for the development of insulin resistance and related metabolic disorders. Long-chain omega 3 fatty acids and a low proportion of saturated fatty acids (SFA) in the phospholipids of the skeletal muscle membranes have been related to a high insulin sensitivity in humans with or without coronary heart disease. The objective of this study was to examine whether a change of dietary fat quality affects insulin sensitivity. A diet with a high proportion of SFA was compared to a diet with the same total fat content but with a high proportion of monounsaturated fatty acids (MUFA). A secondary aim was to investigate the possible effects of a change of fat quality on glucose-induced insulin secretion as well as on serum lipids and lipoproteins and to determine effects of the addition of long-chain n-3 fatty acids to the diet.
The KANWU study included 162 healthy subjects chosen at random to receive a controlled, isoenergetic diet for 3 months containing either a high proportion of SFA or MUFA fatty acids. Within each group there was a second random assignment for supplementation with fish oil (3.6 g omega-3 fatty acids/d) or placebo.
The present research fed up to 37 % of calorie intake as fat, and found that changing the fat quality can effect changes in insulin action of greater than 20%. Insulin sensitivity was significantly impaired on the SFA diet (-10%) but did not change on the MUFA diet (+ 2%). These effects were significantly different between diets. Insulin secretion was not affected. The addition of omega-3 fatty acids did not affect insulin sensitivity or insulin secretion. When total fat intake was below median (37E %), insulin sensitivity was 12.5 % lower and 8.8 % higher on the MUFA and SFA, respectively. Low density lipoprotein cholesterol (LDL) increased on the SFA by 4.1 %, and decreased on the MUFA diet by -5.2. Lipoprotein (a) [Lp(a)] increased on the MUFA diet by 12%.
The addition of n-3 fatty acids to the diet did not, independent of the fatty acid composition of the background diet, affect insulin sensitivity in this study which is consistent with most intervention studies It has been suggested that the n-6:n-3 ratio of skeletal muscle cell membranes might be more important in determining insulin sensitivity than amount of omega 3. Insulin secretion was not affected by a change of dietary fatty acid composition, consistent with some intervention studies.
The beneficial effect of the MUFA diet on insulin sensitivity was not seen when the fat intake was high. However, reducing SFA and increasing MUFA, induced a significant improvement in insulin sensitivity in subjects with lower fat intake. At a high total-fat intake, the positive effects of MUFA with regard to insulin sensitivity were not observed, even if the proportion or total intake of SFA was low. These findings support the importance of both the fatty acid composition and the proportion of total fat in a diet.
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