Fish oil can increase LDL cholesterol, but the effect depends largely on which type of omega-3 you’re taking. The component called DHA is the main driver of LDL increases, while EPA alone tends to have a neutral or slightly lowering effect. In clinical trials, people with high triglycerides who took standard fish oil (which contains both EPA and DHA) saw their total LDL rise by an average of about 13%.
Why DHA Raises LDL but EPA Does Not
Standard fish oil supplements contain two omega-3 fatty acids: EPA and DHA. These two compounds behave very differently when it comes to LDL cholesterol. DHA increases the activity of a protein that transfers cholesterol between different carriers in your blood, which results in more cholesterol ending up in LDL particles. EPA does not trigger this same process.
A pooled analysis of 16 clinical studies on DHA found a significant average increase in LDL of about 7 mg/dL compared to placebo. By contrast, pooled data from nine EPA-only studies showed no meaningful change in LDL. This distinction has real clinical consequences. Prescription EPA-only products do not raise LDL or a related marker called ApoB, while combination EPA/DHA products have increased LDL by as much as 49% in some patient groups compared to placebo.
How Much LDL Typically Rises
The size of the LDL increase varies based on your dose, your baseline triglyceride levels, and the specific product you use. In one study of adults with high triglycerides who took fish oil for 12 weeks, total LDL concentration rose by 13%, or roughly 12 mg/dL. The effect was statistically significant and consistent across participants.
There’s also an interesting mathematical relationship at play: the more your triglycerides drop, the more your LDL tends to rise. One study found that for every 13 mg/dL reduction in triglycerides, LDL increased by about 1 mg/dL. People with the highest starting triglyceride levels experienced the biggest triglyceride drops, which in turn produced the largest LDL increases. This inverse relationship accounted for about 12% of the total change in LDL cholesterol.
At lower doses, the LDL effect is less pronounced. One trial found that a low dose of omega-3s given to people with type 2 diabetes did not produce a significant rise in LDL. The increases in LDL that concern doctors most typically appear at the higher therapeutic doses of 3 to 4 grams per day used to treat very high triglycerides.
The LDL That Rises May Be Less Harmful
Not all LDL particles carry the same risk. Small, dense LDL particles are more strongly linked to heart disease than large, buoyant ones. Fish oil appears to shift the balance toward the larger, less dangerous type. In a study of people with type 2 diabetes already taking a statin, adding 4 grams of omega-3s per day significantly increased LDL particle size compared to taking a statin alone. The ratio of triglycerides to HDL cholesterol also dropped, which is another marker suggesting a shift from small dense LDL to larger particles.
This shift matters for interpreting your lab results. A standard lipid panel only measures the total amount of LDL cholesterol in your blood, not the size or number of particles carrying it. So the LDL number on your lab report might go up after starting fish oil, but the underlying composition of those particles could be less atherogenic (less likely to contribute to plaque buildup). That said, this nuance doesn’t eliminate the concern entirely, especially for people already managing heart disease who need tight LDL control.
EPA-Only vs. Combination Products
This difference between EPA and DHA has shaped how prescription omega-3 products are designed and recommended. Prescription EPA-only formulations do not raise LDL and have shown significant cardiovascular benefits in large clinical trials. Prescription products containing both EPA and DHA lower triglycerides effectively but come with that LDL trade-off. This divergence may help explain why trials using EPA alone (like the REDUCE-IT trial) showed clear reductions in cardiovascular events, while trials using EPA/DHA combinations (like the STRENGTH trial) produced more mixed results.
Most over-the-counter fish oil supplements contain both EPA and DHA, typically in a ratio that provides a meaningful amount of DHA. If you’re taking a store-bought fish oil supplement at modest doses (1 to 2 grams of total fish oil, providing a few hundred milligrams each of EPA and DHA), the LDL impact is generally small. But if you’re taking high doses to manage triglycerides, the DHA content becomes a more important consideration.
What This Means for Your Lipid Panel
If you’ve started fish oil and your next blood test shows higher LDL, the supplement is a likely contributor, particularly if your triglycerides dropped at the same time. This pattern of lower triglycerides paired with higher LDL is the classic fingerprint of DHA’s effect on lipid metabolism.
For people with normal or mildly elevated triglycerides taking standard supplement doses, the LDL increase is usually modest enough that it doesn’t change the overall risk picture. For people with very high triglycerides who need prescription-strength doses (around 4 grams per day), the choice between an EPA-only product and a combination product is worth discussing with a doctor, especially if LDL control is already a priority. The American Heart Association recommends 4 grams per day of prescription omega-3s for managing high triglycerides, and the formulation chosen can meaningfully affect whether LDL goes up, stays flat, or slightly decreases.
Monitoring matters most for people with existing heart disease or those already working to bring LDL down with other medications. Adding a DHA-containing fish oil on top of a statin, for instance, could partially offset the statin’s LDL-lowering effect. In that scenario, an EPA-only option avoids working against your other treatment.