Don’t Worry - Just Focus on Consuming Recommended Amounts of EPA+DHA
If you read any articles suggesting that more omega-3 fatty acids are deposited into the body from krill oil than fish oil, check the citation. A new study by Ghasemifard and colleagues compared the bioavailability and metabolic fate of n-3 fatty acids from krill oil and fish oil in a rat study. There were no diet-related differences in body weight, tissue weights, or whole-body lipid content between the dietary treatments. As the authors note, oil-related differences in apparent n-3 fatty acid digestibility were small, less than 1%.
Rats gained the same amount of weight and accumulated the same amount of whole-body n-3 PUFA on both diets. Because the animals were fed pre-determined rations based on body weight, males were fed more and grew more. Diet-related differences in individual fatty acid content of tissues (mg/g) were found for a few individual fatty acids but the majority were not statistically different. Just remember that the probability of finding a statistical difference increases with the number of comparisons being tested.
The authors acknowledge the limitations of this rat study. In the discussion of the proportion of n-3 PUFA retained in the body of rats from krill vs fish oil, they write, “Importantly, in the present study, it was also clearly shown that the ‘bioavailability’ is in actuality the same, but the resultant metabolic fate is different.” Were there real differences in metabolic fate of n-3 PUFA between krill and fish oils?
Unfortunately, the measures of β-oxidation and metabolic fate were determined by difference and these calculations encompass all the errors common to measuring dietary intake (wastage and orts), fecal excretion (coprophagy) and body fat content. A more accurate approach to measure the metabolic fate of omega-3 fatty acids requires use of isotopically labeled fatty acids.
Earlier this year, the same research group used the same methods to measure the effect of fish oil supplementation regime (daily vs once weekly) on whole body n-3 PUFA content in rats. NutraIngredients captured my thoughts on this differential methodology to measure metabolic fate of long-chain fatty acids.
Mammals are very efficient in digesting and absorbing fat (Moore, 1903). Even though a proportion of the omega-3 fatty acids in krill oil are in triacylglycerol form compared to fish oil, differences in bioavailability are largely statistical arguments.
Don’t obsess about bioavailability. Just consume the recommended 250-500 mg EPA+DHA daily.
Ghasemifard S, Hermon K, Turchini GM, Sinclair AJ. Metabolic fate (absorption, β-oxidation and deposition) of long-chain n-3 fatty acids is affected by sex and the oil source (krill oil or fish oil) in the rat. 2015 Br J Nutr doi: 10.1017/S0007114515002457
Ghasemifard S, Sinclair AJ, Kaur G, Lewandowski P, Turchini GM. What is the most effective way of increasing the bioavailability of dietary long chain omega-3 fatty acids – Daily vs. weekly administration of fish oil? 2015 Nutrients doi: 10.3390/nu7075241
Moore JF. The relative digestibility of some edible fats and oils. Arkansas Agricultural Experiment Station. 1903 Bulletin No. 78.
Burdge G, Calder PC. Conversion of α-linolenic acid to longer-chain polyunsaturated fatty acids in human adults. 2005 Reprod Nutr Dev doi: 10.1051/rnd:2005047
Nichols PD, Kitessa SM, Abeywardena M. Commentary on a trial comparing krill oil versus fish oil. 2014 Lipid Health Dis doi: 10.1186/1476-5111X-13-2
Salem Jr N, Kuratko CN. A reexamination of krill oil bioavailability studies. 2014 Lipids Health Dis doi: 10.1186/1476-511X-13-137