This was the advice I received from a very sharp and nutrition-oriented internist (MD) with whom I met this week. Among other things, he encouraged me to cut open one of my capsules and just smell it. I did so and WOW -- the odor was overpowering! The oil in the capsules seems clearly rancid, and I've now tossed the remainder. By comparison, my bottle of Carlson's Fish Oil, kept refrigerated since opening, had no hint of odor and seems to be a much better choice.
According to the internist, most if not all fish oil capsules are rancid -- "it's very difficult to encapsulate fish oil without it turning rancid." So my particular brand .is apparently not out of the ordinary.
Based on the above, you just might want to cut one of your fish oil capsules and see if it passes the "smell test". Incidentally, I have nothing against fish oil capsules (been taking them regularly) or any personal interest in Carlson's Fish Oil. It happens to be what I have and also what the internist recommends.
I was quite surprised by the result of this simple experiment and thought I'd pass it along to those of you who also include fish oil in your supplement regimens.
Bill