Fish oil diets do not improve insulin sensitivity and secretion in healthy adult male pigs

The effects of long-term dietary supplementation of fish oil (n-3 PUFA-rich) in adult male pigs on body condition as well as insulin sensitivity and secretion were examined. Fifteen Duroc boars aged 204·5 (sd 9·4) d (body weight 145·8 (sd 16·8) kg) received daily 2·5 kg basal diet with a supplement of: (1) 62 g hydrogenated animal fat (n 5); (2) 60 g menhaden oil containing 10·8 g DHA and 9·0 g EPA (n 6); (3) 60 g tuna oil containing 19·8 g DHA and 3·9 g EPA (n 4). Rations were balanced to be isoenergetic. After 7 months of treatments, oral glucose and meal tolerance tests were conducted after insertion of a catheter into the jugular vein. Dietary supplementation with n-3 PUFA altered the blood plasma profile: DHA and EPA increased whereas arachidonic acid decreased (P < 0·01). Plasma glucose, insulin and C-peptide responses to oral glucose and the test meal were not affected by treatments (P>0·34). For all animals, total body fat estimated from body weight and back fat thickness was correlated with both β-cell function (by homeostasis model assessment (HOMA); r+0·63) and insulin sensitivity (index of whole-body insulin sensitivity and by HOMA; r − 0·63 and r+0·66, respectively). In conclusion, long-term supplementation with dietary n-3 PUFA did not affect insulin metabolism in healthy adult male pigs. The relationship between body fat and insulin sensitivity, well documented in human subjects, suggests that the adult male pig could be a promising animal model for studies on insulin metabolism.