Siv Tengblad

Desaturation and Elongation of Fatty Acids and Insulin Action

Abstract: Insulin resistance is characterized by specific changes of the composition of fatty acids in the serum lipids and in the skeletal muscle membranes. Impaired insulin sensitivity is associated with high proportions of palmitic (16:0) acid and low levels of linoleic (18:2 n‐6) acid in serum. In addition, there are apparent changes of the fatty acid desaturase activities, suggesting an increased activity of the Δ9 and Δ6 desaturases and a decreased activity of the Δ5 desaturase. The activity of the fatty acid desaturases is regulated by long‐chain polyunsaturated fatty acids and insulin and is probably also dependent on the degree of physical activity. A high ratio between arachidonic (20:4 n‐6) and dihomo‐gamma linolenic (20:3 n‐6) acid, as a measure of Δ5 desaturase activity, in the skeletal muscle phospholipids has been related to good insulin sensitivity. Available knowledge seems to indicate that the degree of saturation of the body lipids, and especially the proportion of palmitic acid in the lipid membranes, may be critical for insulin sensitivity. The strong relationships between the Δ5 desaturase activity, a high content of long‐chain polyunsaturated fatty acids in the skeletal muscle, and insulin sensitivity may be due to parallel effects of diet and/or physical activity on the fatty acid composition and on insulin sensitivity.

Effects of dietary phenolic compounds on tocopherol, cholesterol, and fatty acids in rats.

The effects of the phenolic compounds butylated hydroxytoluene (BHT), sesamin (S), curcumin (CU), and ferulic acid (FA) on plasma, liver, and lung concentrations of α- and γ-tocopherols (T), on plasma and liver cholesterol, and on the fatty acid composition of liver lipids were studied in male Sprague-Dawley rats. Test compounds were given to rats ad libitum for 4 wk at 4 g/kg diet, in a diet low but adequate in vitamin E (36 mg/kg of γ-T and 25 mg/kg of α-T) and containing 2 g/kg of cholesterol. BHT significantly reduced feed intake (P<0.05) and body weight and increased feed conversion ratio; S and BHT caused a significant enlargement of the liver (P<0.001), whereas CU and FA did not affect any of these parameters. The amount of liver lipids was significantly lowered by BHT (P<0.01) while the other substances reduced liver lipid concentrations but not significantly. Regarding effects on tocopherol levels, (i) feeding of BHT resulted in a significant elevation (P<0.001) of α-T in plasma, liver, and lung, while γ-T values remained unchanged; (ii) rats provided with the S diet had substantially higher γ-T levels (P<0.001) in plasma, liver, and lung, whereas α-T levels were not affected; (iii) administration of CU raised the concentration of α-T in the lung (P<0.01) but did not affect the plasma or liver values of any of the tocopherols; and (iv) FA had no effect on the levels of either homolog in the plasma, liver, or lung. The level of an unknown substance in the liver was significantly reduced by dietary BHT (P<0.001). BHT was the only compound that tended to increase total cholesterol (TC) in plasma, due to an elevation of cholesterol in the very low density lipoprotein + low density lipoprotein (VLDL+LDL) fraction. S and FA tended to lower plasma total and VLDL+LDL cholesterol concentrations, but the effect for CU was statistically significant (P<0.05). FA increased plasma high density lipoprotein cholesterol while the other compounds reduced it numerially, but not significantly. BHT, CU, and S reduced cholesterol levels in the liver TC (P<0.001) and percentages of TC in liver lipids (P<0.05). With regard to the fatty acid composition of liver lipids, S increased the n-6/n-3 and the 18∶3/20∶5 polyunsaturated fatty acids (PUFA) ratios, and BHT lowered total monounsaturated fatty acids and increased total PUFA (n−6+n−3). The effects of CU and FA on fatty acids were not highly significant. These results suggest some in vivo interactions between these phenolic compounds and tocopherols that may increase the bioavailability of vitamin E and decrease cholesterol in rats.

Lower tocopherol serum levels in subjects with abdominal adiposity

Abstract. Objectives. Peroxidation of lipoproteins may be of critical importance in the development of atherosclerosis. Tocopherol is considered to be the most effective lipid‐soluble antioxidant. The main aim of this study was to measure the serum tocopherol concentrations in a Swedish reference population and to relate them to family history, lifestyle and serum lipoprotein composition.

Dairy products and metabolic effects in overweight men and women: results from a 6-mo intervention study

BACKGROUND Some epidemiologic studies have suggested inverse relations between intake of dairy products and components of the metabolic syndrome. OBJECTIVE The objective was to investigate the effects of an increased intake of dairy products in persons with a habitually low intake on body composition and factors related to the metabolic syndrome. DESIGN Middle-aged overweight subjects (n = 121) with traits of the metabolic syndrome were recruited in Finland, Norway, and Sweden and randomly assigned into milk or control groups. The milk group was instructed to consume 3-5 portions of dairy products daily. The control group maintained their habitual diet. Clinical investigations were conducted on admission and after 6 mo. RESULTS There were no significant differences between changes in body weight or body composition, blood pressure, markers of inflammation, endothelial function, adiponectin, or oxidative stress in the milk and the control groups. There was a modest unfavorable increase in serum cholesterol concentrations in the milk group (P = 0.043). Among participants with a low calcium intake at baseline (<700 mg/d), there was a significant treatment effect for waist circumference (P = 0.003) and sagittal abdominal diameter (P = 0.034). When the sexes were analyzed separately, leptin increased (P = 0.045) and vascular cell adhesion molecule-1 decreased (P = 0.001) in women in the milk group. CONCLUSIONS This study gives no clear support to the hypothesis that a moderately increased intake of dairy products beneficially affects aspects of the metabolic syndrome. The apparently positive effects on waist circumference and sagittal abdominal diameter in subjects with a low calcium intake suggest a possible threshold in relation to effects on body composition.

Malondialdehyde concentration in plasma is inversely correlated to the proportion of linoleic acid in serum lipoprotein lipids

It has been suggested that the susceptibility of low density lipoprotein (LDL) to oxidative stress depends on the balance between its contents of polyunsaturated fatty acids and antioxidants. In a healthy reference population (n = 103), the plasma concentration of malondialdehyde (MDA) (mean 0.86, range 0.50-1.27 mumol/l) was positively correlated to the serum concentrations of LDL cholesterol (r = 0.31, P = 0.001), very low density lipoprotein triglycerides (r = 0.25, P = 0.009) and apolipoprotein B (r = 0.23, P = 0.03), and negatively correlated to lipid corrected alpha tocopherol in serum (r = -0.22, P = 0.02) and lipoprotein(a) (Lp(a)) (r = -0.26, P = 0.01). Plasma MDA was negatively correlated to the content of linoleic acid in the serum lipoprotein phospholipids (r = -0.35, P = 0.0008). In a stepwise regression analysis 12% of the variation in plasma MDA was explained by variations in the content of linoleic acid and 27% after addition of Lp(a) and abdominal sagittal diameter. The significant negative relation between plasma MDA and the amount of linoleic acid in the lipoprotein lipids indicates that other factors, e.g. the availability of anti-oxidants and the lipoprotein metabolism, may be of greater importance for intravascular lipid peroxidation than the proportion of polyunsaturated fatty acids in the lipoprotein lipids.

Indices of fatty acid desaturase activity in healthy human subjects : effects of different types of dietary fat

Δ9-Desaturase (stearoyl-CoA desaturase 1, SCD-1) regulates the desaturation of SFA, mainly stearic and palmitic, to MUFA. Δ6-Desaturase (D6D) and Δ5-desaturase (D5D) are involved in the metabolism of linoleic and α-linolenic acid to polyunsaturated metabolites. The objective of the present study was to study the effects of different types of dietary fat on indices of fatty acid desaturase (FADS) activity (evaluated as product:precursor ratios) in plasma and skeletal muscle in human subjects. A high SCD-1 index has been related to obesity and metabolic disorders, while the D5D index is associated with insulin sensitivity. Fatty acid composition of serum and skeletal muscle lipids was analysed by GLC during a randomised, controlled, 3-month dietary intervention in healthy subjects. A comparison of the effects of a diet containing butter fat (SFA, n 17) with a diet containing monounsaturated fat (MUFA, n 17), keeping all other dietary components constant, showed a reduced SCD-1 activity index by 20% on the MUFA diet compared with the SFA diet assessed in serum cholesteryl esters. The D6D and D5D indices remained unaffected. Supplementation with long-chain n-3 fatty acids reduced the SCD-1 index by a similar magnitude while the D6D index decreased and the D5D index increased. It is concluded that changes in the type of fat in the diet affect the indices of FADS activity in serum and skeletal muscle in human subjects. The desaturase activity indices estimated from the serum lipid ester composition are significantly related to corresponding indices studied in skeletal muscle phospholipids.

Omega-3 polyunsaturated essential fatty acids are associated with depression in adolescents with eating disorders and weight loss

Aim:  To study the relationship between polyunsaturated fatty acids (PUFA) status and depression in adolescents with eating disorders (ED) and weight loss.

Essential fatty acid status in teenage girls with eating disorders and weight loss

Aim:  To explore the relationship between essential fatty acids (FA) and weight changes in adolescent girls with eating disorders (ED).