Journal Name:
Nutr. Metab. Cardiovasc. Dis.

Article Title:
Effects of saturated and unsaturated fatty acids on estimated desaturase activities during a controlled dietary intervention.

Date Written:
2008

Volume:
18

Number:
10

Page:
683

Author(s):
Warensjö, E.; Risérus, U.; Gustafsson, I.B.; Mohsen, R.; Cederholm, T.; Vessby, B.

Article:
Quality rather than the quantity of dietary fat (FA) is most important for the development of cardiovascular disease. The relative proportions of FA in blood lipids can be used as biomarkers of dietary FA and are known to change as a consequence of an alteration in dietary fat quality during intervention. The desaturating enzymes, D9-desaturase (also referred to as stearoyl-CoA-desaturase (SCD)), D6-desaturase (D6D) and D5-desaturase (D5D), introduce cis-double bonds in the carbon chain of long chain FA. These enzymes catalyze the synthesis of long chain monounsaturated FA (MUFA) and polyunsaturated FA (PUFA). The study of desaturase activities directly in sub-cellular microsomal (i.e. endoplasmic reticulum) fractions is complicated in humans and not feasible in clinical studies.

Data in humans on how the surrogate measures of desaturase activities in serum change in response to shifts in dietary fat quality are however largely lacking. This is of clinical interest, since estimated desaturase activities have predicted metabolic risks, even when other risk factors were taken into account. Therefore, the objective of this study was to estimate desaturase activities and FA composition in serum cholesteryl esters (CE) and phospholipids (PL) induced by two different diets; one high in unsaturated fat, based on canola/rapeseed oil (RO-diet) and one a diet high in saturated fatty acids (SFA), mostly from butter (SAT-diet) in a strictly controlled cross-over study effects In a two-period (three weeks) study, 20 subjects (six women and 14 men) consumed a diet high in saturated fat (SAT-diet) and a canola/rapeseed oil diet (RO-diet), rich in oleic acid (OA), linoleic acid (LA) and alpha-linolenic acid (ALA). Estimated desaturase activities were calculated as precursor to product FA ratios in serum cholesteryl esters and phospholipids. The estimated SCD [16:1 n-7/16:0] and Delta(6)-desaturase [20:3 n-6/18:2 n-6] was significantly higher while Delta(5)-desaturase [20:4 n-6/20:3 n-6] was significantly lower in the SAT-diet (P<0.001 for all), compared to the RO-diet. The serum proportions of palmitic, stearic, palmitoleic and dihomo-gamma-linolenic acids were significantly higher in the SAT-diet while the proportions of LA and ALA were significantly higher in the RO-diet. The content of 16:1 was higher in the SAT-diet than in the RO diet, which may then have affected the ratio of relevant serum lipid esters.

Although the intake of ALA was almost four times higher during the RO-period compared to the SAT-period, most serum long chain n-3 FA did not significantly differ between the two test periods. This result is however not surprising since the conversion of LA and ALA competes for the same desaturases (D5D and D6D) and the synthesis of n-3 long chain FA from ALA is more effective when the intake of SFA is higher and LA is lower. The serum proportion of arachidonic acid (AA), which is formed from LA, did not differ significantly between the two test diets, although LA was 2.5 times higher in the RO-diet. Again this is not surprising since AA is tightly regulated across membranes.

This is the first study to demonstrate that surrogate measures of desaturase activities change as a consequence of an alteration in dietary fat quality. The estimated SCD-16 and D6D increased while D5D decreased after a high SFA diet, compared to an canola/RO-diet. Both the [16:1/16:0]-ratio and 16:1 seem to reflect changes in saturated fat intake and may be useful markers of saturated fat intake in Western countries. The SCD-18 ratio would not be such a good marker, since the high dietary content of OA will ‘‘dilute’’ endogenously synthesized OA (18:0/18:1 n-9) and thus affect the ratio in serum. The proportion of 16:1 in serum PL was significantly reduced after the MUFA diet, while the proportion of OA increased. At the same time was 16:0 in serum lipids slightly lowered and 18:0 not affected by the canola/rapeseed MUFA diet.

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