There are three forms of omega-3s found in supplements; triglycerides, ethyl esters, or phospholipids (see Figure 1). As more retail brands than ever tout the superiority of one form over the other through “on-pack” claims and whether one form is “more natural”, it’s easy to get confused about what they really are.
A natural triglyceride found in fish has a glycerol “backbone” with three fats attached. There is usually only one omega-3 connected at the middle arm, while the two outside arms usually contain other fats like omega-6 and saturated fats. Standard fish oils remain in a natural triglyceride form where the structure hasn’t been altered and contain approximately 30% EPA and DHA.
Phospholipid omega-3’s are found in krill oil and instead of having three fats connected to the glycerol backbone, they contain two fats with the third arm consisting of phosphate and choline.
Figure 1: Triglyceride and ethyl ester forms of omega-3’s (adapted from Ackman 1989, Holmer 1989)
The production of the ethyl ester form of EPA and DHA is an essential and necessary step for obtaining omega-3 oils that are higher than 30% concentration. To achieve this, the natural triglyceride form needs to be changed to ethyl ester omega-3’s by completely removing them from the backbone. Once this process is complete, they are then concentrated and purified through molecular distillation. When the desired concentration is achieved, many fish oil manufacturers convert the ethyl ester omega-3’s back to a triglyceride form, whereas others maintain the purified oil in the ethyl ester form.
Some companies state that the reassembled triglyceride form is a “natural triglyceride”. They are more correctly called “resynthesized triglycerides” because they have had to be reassembled and now the triglyceride form has two to three omega-3’s attached to the glycerol backbone, when the original natural form only had one omega-3 attached (Ackman, 1989, Holmer, 1989).