Fish oil, insulin sensitivity, insulin secretion and glucose tolerance in healthy people: is there any effect of fish oil supplementation in relation to the type of background diet and habitual dietary intake of n-6 and n-3 fatty acids?
OBJECTIVE
To evaluate whether a moderate supplementation of long-chain n-3 fatty acids is able to modulate insulin sensitivity, insulin secretion, beta-cell function and glucose tolerance in healthy individuals consuming a diet rich in either saturated or monounsaturated fat, also in relation to their habitual dietary intake of n-6 and n-3 fatty acid.


RESULTS
One hundred and sixty-two healthy individuals were randomly assigned to follow either one of two isoenergetic diets for 3 months, one rich in monounsaturated fats and the other rich in saturated fats. Within each group there was a second randomisation to fish oil (n-3 fatty acids 3.6 g/day) or placebo. At the beginning and at the end of the treatment periods insulin sensitivity (SI), first phase insulin response (FPIR) and glucose tolerance (K(G)-value) were evaluated by the intravenous glucose tolerance test (IVGTT). Fish oil did not have any effect on SI, FPIR, K(G)-value and disposition index in either diet. Even after dividing subjects according to the median value of n-6/n-3 ratio of serum phospholipids at baseline, there was no change in SI (Delta SI 0.42+/-0.34 on fish oil vs 0.14+/-0.23 on placebo for those with n-6/n-3 <4.85; -1.03+/-0.47 on fish oil vs -0.27+/-0.32 on placebo for those with n-6/n-3 >4.85) (M+/-SE), FPIR (Delta FPIR 135.9+/-78.9 vs 157.2+/-157.5 pmol/L; 38.8+/-181.7 vs 357.1+/-181.7 pmol/L), K(G)-value (Delta K(G) 0.14+/-0.15 vs 0.12+/-0.11; -0.32+/-0.16 vs 0.15+/-0.15) or disposition index (Delta disposition index 1465.4+/-830.4 vs 953.8+/-690.0; -1641.6+/-1034.3 vs 446.6+/-905.1). Considering the 75th percentile of n-6/n-3 ratio (5.82) the results on insulin sensitivity, insulin secretion and disposition index were confirmed, while, in this more extreme situation, n-3 fatty acid supplementation induced a significant deterioration of K(G)-value (p=0.02).


CONCLUSIONS
In healthy individuals a moderate supplementation of fish oil does not affect insulin sensitivity, insulin secretion, beta-cell function or glucose tolerance. The same is true even when the habitual dietary intake of n-6 and n-3 fatty acids is taken into account.
Giacco
Rosalba
R
Institute of Food Science, Italian National Research Council, Avellino, Italy. rgiacco@isa.cnr.it <rgiacco@isa.cnr.it>
Cuomo
Vincenzo
V
Vessby
Bengt
B
Uusitupa
Matti
M
Hermansen
Kjeld
K
Meyer
Barbara J
BJ
Riccardi
Gabriele
G
Rivellese
Angela A
AA
D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000378:metabolism*; D015992:Body Mass Index; D004041:Dietary Fats / Q000008:administration & dosage; D004042:Dietary Fats, Unsaturated / Q000008:administration & dosage; D019587:Dietary Supplements; D015525:Fatty Acids, Omega-3 / Q000008:administration & dosage*; D043371:Fatty Acids, Omega-6 / Q000008:administration & dosage*; D005247:Feeding Behavior; D005260:Female; D005395:Fish Oils / Q000008:administration & dosage* / Q000737:chemistry; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D000078790:Insulin Secretion; D008297:Male; D008875:Middle Aged
D001786:Blood Glucose; D004041:Dietary Fats; D004042:Dietary Fats, Unsaturated; D015525:Fatty Acids, Omega-3; D043371:Fatty Acids, Omega-6; D005395:Fish Oils; D007328:Insulin