Comparative Effects of the Fat Extracted from Raw and Fried Sardines Upon Rat Growth and Zinc Bioavailability

Three diets containing 8% olive oil, fresh sardine (Clupea pilchardus) oil and oil from sardines fried in olive oil were prepared. After in vitro digestion, soluble (dialysed and non-dialysed) and insoluble zinc fractions were determined. Fresh sardine oil and oil from sardines fried in olive oil provided more dialysed zinc and less insoluble zinc than 8% olive oil. Three groups of growing rats consumed the diets for 28 days. Food intake and body weight values of rats fed 8% olive oil were significantly higher than those fed fresh sardine oil and slightly lower than those fed oil from sardines fried in olive oil. Animals fed fresh sardine oil exhibited the lowest apparent zinc retention during days 5-12, but absorption efficiency increased during days 21-28 and all groups had similar final zinc absorption and retention values. Animals fed oil from sardines fried in olive oil displayed higher (days 5-12) or similar (days 21-28) apparent zinc absorption and retention values than rats fed 8% olive oil and fresh sardine oil. Hepatic zinc concentrations were higher in rats fed oil from sardines fried in olive oil than fed fresh sardine oil, while all groups showed similar spleenic concentrations. Zinc accumulation in skin was significantly higher in animals fed fresh sardine oil than in those fed oil from sardines fried in olive oil, and their total erythrocyte zinc concentrations were also higher than in rats fed oil from sardines fried in olive oil or on 8% olive oil. In conclusion, a diet high in raw sardine fatty acids can cause excessive zinc accumulation in skin and erythrocytes. However, these negative effects of sardine oil disappear after frying in olive oil.