The question of a potential superiority between the forms – fish oil, which has omega-3 in triglyceride forms, and krill oil, which delivers omega-3 in phospholipid form – is a relatively recent debate.
A recent study comparing the bioavailability of 1.3 grams of EPA and DHA per day from krill oil or fish oil with omega-3s in the triglyceride or ethyl ester forms found that there were no differences in blood levels of the omega-3s.
‘We’re banging each other’s heads with bioavailability’
“I appreciate that people are doing comparisons on equal doses, and I must applaud that part of the study,” said Dr Nils Hoem, Chief Scientist, Aker BioMarine Antarctic AS, told NutraIngredients-USA. “It was a nice study with respect to the clinical conduct, but the data handling was confused. The fundamental problem is that you are comparing apples and oranges.
“Fish oil has a place with us,” he stressed. “Krill oil and fish oil address different needs, and kinetically they are different. Triglycerides and phospholipids are completely different molecules. The fundamental question is how are they taken up?”
“This study was just one study in the omega-3 field,” he said. “We’re banging each other’s heads with bioavailabilities and it has to stop. It’s a real waste of time.”
‘One data point’
Jim Hamilton, CEO of Neptune Technologies and Bioressources, also told us that this study is just one data point. “Having lived on both sides of the debate [Hamilton was previously President of DSM Nutritional Products USA], it is important to not over-react to one data point,” he said.
“According to GOED, there are about 27,000 studies done with omega-3s and the vast majority of those are positive – about 82%, I think. However, when a new study comes out people go, “a-ha! A conclusion!” But the world doesn’t work that way.
“When we look at the domain of bioactivity, from our perspective the vast majority of science shows that krill is more active than fish oil.”
‘We need to stop talking about omega-3 bioavailability’
One of the problems Dr Hoem has with the recent fish vs krill study is how it tried to look at accumulated amounts. “There is something important with EPA and DHA,” he said. “When you look at the other fats, from 18C and down towards 16C and 14C, these are taken up in about two hours and gone in about 10 hours. But one meal of salmon will have EPA and DHA washing around in the plasma for three days. Our bodies are processing EPA and DHA for a long time after it’s been eaten.”
DHA has a much longer half-life than EPA, he added, and internal Aker data has indicated that accumulation of the fatty acid is so slow that it’s really hard to estimate the half-life. What is sure is that DHA is not at steady state at four weeks, he said.
“The assumption is that we reach steady state for both omega-3s at four weeks,” he said. “For EPA, that is not an unreasonable assumption (you need about 30 days), but the only way to be certain is to study for longer than that. For DHA, it continues to accumulate. The body really likes DHA, and the accumulation is so slow that it may look like you’re at steady state but you’re not. You’d only know by continuing the supplementation. But I don’t expect anyone to supplement for 12 months to find out how long”
Dr Hoem also questioned why the accumulated levels were not compared with the baseline levels for each participant, as opposed to the absolute levels used in the study. This effectively obscures the question, ‘What is the relative difference in accumulation over time, when taking the same dose of EPA and DHA, but in different forms?’, he said. This question can only be answered by looking at the relative change from baseline.
The numbers in the Lipids in Health & Disease paper indicated that the ethyl esters are at the lowest level [with a mean plasma EPA + DHA levels at four weeks of 91 ug/mL], triglycerides are intermediate [with mean levels of 108 ug/mL], and phospholipids are the highest [a mean level of 119 ug/mL at four weeks]. The differences have a p value of 0.052, so just shy of statistical significance, leading the researchers to conclude that the bioavailability is similar.
But looking at the relative change leads to differences, with percentage increases from mean baseline values to mean final values of 119% in the ethyl ester group, 153% in the triglyceride group, and 216% in the krill oil group.
“This is pretty much what we’ve seen in other studies,” said Dr Hoem. But while he has problems with the study, he still thinks that the focus should not be on bioavailability but on the differential distribution into the tissues.
“EPA and DHA don’t have their actions in the blood stream. Their activity comes when they are incorporated into the membranes, or in the membranes of the organs, or when transported into the brain. The tissue is the issue.”
So what does happen when the omega-3s are taken up by the body, and into which tissues they go, triglycerides vs phospholipids?
“We’ve been able to show using radio-labeling that triglycerides go through lymph, and a far smaller proportion of phospholipids go through lymph,” said Dr Hoem. “When we follow this over time we see clear differences in the flux in and out of different organs. For example, far more EPA is stored in white fat cells (adipocytes) when bound to triglycerides, compared to EPA bound to phospholipids.
“It will take a lot more research to elucidate the whole pattern and fluxes in and out of the tissues.”