The Nation's Health + [Omega-3 fatty acids]

Omega-3 fatty acids: Does fish oil raise LDL cholesterol?

Katie had an LDL (conventionally calculated) of 87 mg/dl, HDL of 48 mg/dl.

She added fish oil, 6000 mg per day. Three months later her LDL was 118 mg/dl, HDL 54 mg/dl. In other words, LDL increased by 31 mg. What gives?

Several studies have, indeed, shown that fish oil raises LDL cholesterol, usually by 5-10 mg/dl. Occasionally, it may be as much as 20-30.

Unfortunately, many physicians often assume that it's the (minor) cholesterol content of fish oil capsules, or some vague, undesirable effect of fish oil. It's nothing of the kind.

Since we based Katie's program on (NMR) lipoprotein analysis, not conventional lipids (HDL, calculated LDL, triglycerides, total cholesterol), I knew that Katie also had a severe excess of intermediate-density lipoprotein, or IDL, and very-low density lipoproteins, VLDL. This signifies that after a meal, dietary fats persist for 12, 24,or more hours. Fish oil is a very effective method to clear IDL and VLDL, though sometimes it also causes a shift of some IDL and VLDL into the LDL class. Thus, the apparent increase in LDL.

Another contributor: Conventional LDL is a calculated value, not measured. The calculation for LDL is thrown off by any reduction in HDL or rise in triglycerides. In Katie's case, the rise in HDL from 48 to 54 means that calculated LDL is becoming more accurate and rising towards the true measured value. At the start, Katie's true measured LDL was 122 mg/dl, 35 mg higher than the calculated value. Calculated LDL is therefore approximating measured LDL more accurately as HDL rises.

The most important lesson to learn is that, if LDL rises significantly on fish oil and you haven't had lipoproteins formally measured, there may have been a substantial postprandial abnormality like IDL that was unrecognized.