Neither fish oil nor krill oil is definitively “better.” When matched for the same dose of omega-3 fatty acids (EPA and DHA), both oils lower triglycerides by a nearly identical amount and produce similar changes in blood lipid markers. The real differences come down to absorption mechanics, omega-3 concentration per capsule, added nutrients, and cost.
How the Omega-3s Differ at a Molecular Level
The omega-3 fatty acids in fish oil are bound to triglycerides, the same fat storage molecule your body uses. In krill oil, 30% to 65% of the fatty acids are bound to phospholipids instead, specifically phosphatidylcholine. Phospholipids are the building blocks of cell membranes, and there’s reason to believe this form may pass through the intestinal wall more efficiently. In a four-week crossover trial with 24 healthy adults taking 600 mg of EPA and DHA daily, krill oil raised plasma EPA levels significantly more than fish oil did at the same dose. Both oils raised DHA and the overall omega-3 index comparably.
This phospholipid advantage is real but easy to overstate. The absorption edge appears modest, and it hasn’t consistently translated into better clinical outcomes in head-to-head trials. Think of it as a slight efficiency gain, not a game-changer.
Omega-3 Content Per Capsule
This is where fish oil has a clear, practical advantage. A standard fish oil softgel contains roughly 300 to 2,250 mg of combined EPA and DHA, depending on the formulation. A krill oil softgel typically delivers just 45 to 200 mg. That means you may need to take several krill oil capsules to match what a single concentrated fish oil capsule provides.
If your goal is hitting a specific daily omega-3 target (say, 1,000 mg of EPA plus DHA for heart health), fish oil gets you there in fewer pills. Krill oil’s potential absorption advantage narrows this gap somewhat, but it doesn’t close it entirely.
Effects on Cholesterol and Triglycerides
A network meta-analysis pooling data from multiple randomized trials found that the lipid-lowering effects of krill oil and fish oil do not meaningfully differ. Both oils lowered triglycerides compared to placebo. When researchers calculated the reduction per gram of omega-3s consumed, fish oil lowered median triglycerides by about 9.0 mg/dL and krill oil by about 9.8 mg/dL. The difference between those numbers was not statistically significant. LDL cholesterol, HDL cholesterol, and total cholesterol also showed no significant difference between the two oils. The takeaway from that analysis was straightforward: the triglyceride reduction depends on how much EPA and DHA you actually consume, not which oil delivers it.
Krill Oil’s Antioxidant Bonus
Krill oil contains astaxanthin, the pigment that gives it a reddish color. Astaxanthin is a potent antioxidant that works through multiple pathways: it scavenges reactive oxygen species, activates your body’s own antioxidant enzyme systems, and helps protect cells from oxidative damage. Animal studies have shown krill oil feeding reduced oxidative damage in the liver by boosting protective enzymes and lowering markers of cell damage.
Astaxanthin also appears to improve insulin sensitivity and glucose metabolism in early research, with potential relevance for people managing blood sugar. Fish oil does not contain astaxanthin. If antioxidant protection matters to you alongside omega-3 intake, krill oil offers something fish oil simply doesn’t. That said, human trials comparing the two oils found no marked differences in blood markers of oxidative stress or inflammation, so the practical benefit in people (rather than lab animals) remains uncertain.
Krill Oil Also Affects More Metabolic Pathways
Gene expression studies have revealed an interesting distinction. Fish oil tends to upregulate cholesterol synthesis pathways, while krill oil does the opposite. Krill oil also influenced glucose metabolism, fatty acid metabolism, and lipid metabolism pathways that fish oil left untouched. Researchers attribute this broader metabolic reach to the phospholipid structure of krill oil’s omega-3s. Whether these molecular-level differences translate into meaningful health differences over years of supplementation is still an open question.
Contaminants and Purity
Krill sit near the bottom of the ocean food chain, which generally means less accumulation of heavy metals like mercury. Testing of commercial products confirms that krill oil tends to carry lower levels of PCBs (industrial pollutants) than most fish oil products. However, the picture isn’t entirely clean. Antarctic krill oil products carried the highest levels of certain chlorinated pesticide residues among all supplements tested, particularly hexachlorobenzene, a persistent pollutant that concentrates in the Antarctic food web. Some krill oil products also contained multiple detectable dioxin-related compounds, while fish oil products typically showed fewer.
In practical terms, all tested products fell well within safety limits, with contaminant levels at tiny fractions of tolerable daily intake thresholds. Neither type of oil poses a meaningful toxicity risk at normal supplement doses.
Side Effects and Tolerability
Omega-3 supplements in general can cause unpleasant taste, fishy burps, heartburn, nausea, and diarrhea. These side effects are usually mild. Many krill oil users report fewer fishy aftertaste problems compared to fish oil, likely because the smaller capsule size and phospholipid-bound fats digest differently. If fish oil burps have driven you away from omega-3 supplements in the past, krill oil may be easier to tolerate. Enteric-coated fish oil capsules can also reduce this issue, though.
Cost Per Gram of Omega-3
Krill oil is significantly more expensive than fish oil on a per-milligram-of-omega-3 basis. Because each krill oil capsule contains so much less EPA and DHA, you’re paying more to reach the same daily dose. A month’s supply of concentrated fish oil delivering 1,000 mg of EPA plus DHA daily might cost $10 to $20, while reaching the same omega-3 intake from krill oil could cost three to five times as much. The phospholipid form and added astaxanthin account for some of that premium, but much of it is simply lower omega-3 concentration per capsule.
Which One Should You Choose
If your primary goal is getting a therapeutic dose of omega-3s as affordably and efficiently as possible, fish oil is the better choice. It delivers far more EPA and DHA per capsule, costs less, and produces the same triglyceride-lowering results gram for gram.
Krill oil makes more sense if you value the added antioxidant from astaxanthin, want a supplement that may absorb slightly more efficiently at lower doses, prefer smaller capsules, or have trouble tolerating fish oil’s side effects. Its phospholipid-based omega-3s also appear to influence a broader set of metabolic pathways, which could matter over the long term even though clinical trials haven’t yet shown a clear health advantage.
For most people on a budget who just want reliable omega-3 supplementation, fish oil remains the practical winner. For those willing to pay a premium for a more complex nutritional profile and better tolerability, krill oil is a reasonable alternative, not a magic upgrade.