Fish Oil, Oxidation, and the Truth About “Rancidity”

Omega-3 supplements are at the center of a controversy regarding their oxidation levels and potential harm. This presentation addresses the gap between claims of harm and the available human data, explaining how oxidation is measured and interpreted. 

00:00 Introduction to Omega-3 Supplements

00:49 Understanding Oxidation in Fish Oil

01:10 Measuring Oxidation: Peroxide, Anisidine, and Totox Values

01:50 The Flavoring Problem in Oxidation Testing

02:46 Market Surveys and Oxidation Failures

04:08 Do Oxidation Standards Correlate with Human Harm?

04:30 Clinical Trials on Oxidized Fish Oil

06:54 Regulatory Perspectives on Oxidation and Safety

07:57 Summary and Takeaways

09:08 Conclusion and References

Chapters

• 0:00 The Oxidation Paradox
• 0:21 Why Omega-3s Matter
• 1:04 How Oxidation Is Measured
• 1:50 The Flavoring Problem
• 2:56 Market Failures And Patterns
• 4:08 Do Oxidation Limits Predict Harm
• 4:30 The 2012 Human Trial Design
• 5:12 Results: No Short-Term Harm
• 6:34 What Regulators Acknowledge
• 7:23 Limits Of Current Evidence
• 8:17 Nuanced Takeaways And Closing

Transcript

SPEAKER_00: 0:00

Omega-3 supplements sit at the center of a contradiction. Oxidation is measurable and common in the market, yet claims of harm often outpace the human data. This presentation is meant to examine that gap, how oxidation is measured, how those numbers are interpreted, what the evidence actually supports regarding quality safety and testing in omega-3 supplements. Approximately two-thirds of adults and 95% of children in the United States fall short of dietary omega-3 guidelines. Fish oil-based supplements are usually positioned to help us meet or exceed those recommendations based on personal health goals. The clinical promise of fish oil comes from its polyunsaturated fatty acids, specifically EPA and DHA. These omega-3s are consistently associated with cardiovascular benefits, including reduced risk of coronary heart disease and coronary heart disease-related mortality. The benefit of fish oil comes from its structure, but that same structure is also considered its weakness. EPA and DHA, the primary fatty acids in fish oil, contain multiple double bonds, which make them highly sensitive to things like heat, light, and oxygen. Over time, that exposure causes the oil to oxidize or go rancid, as some people call it. We measure this oxidation in stages. Peroxide value captures early oxidation products. Inicidine value reflects later stage breakdown products. These are mainly aldehydes, that's important to remember. Lastly, totox stands for total oxidation value. This simply combines both previous values into a single number meant to summarize overall oxidation. The limits shown here, and this is important, peroxide value of 5, anisidine of 20, and totox of 26 are not safety thresholds. They're voluntary quality benchmarks set by the industry to assess freshness and stability of oil, so they serve as quality benchmarks, not safety. This slide highlights what's often called the flavoring problem. The primary issue is that the anisidine value test is what's called a colorometric test, and it's not chemically specific. The anisidine value is designed to detect aldehydes formed during oxidation, but many flavorings, especially citrus and lemon flavors, which are commonly used in fish oils, naturally contain aldehydes as well. The test cannot distinguish between aldehydes coming from oxidation and aldehydes coming from added flavorings. As a result, flavored oils can show an artificially high anisidine value and therefore a high totox score, even when the underlying oil itself is not highly oxidized. Because of this limitation, the global organization of EPA and DHA monograph explicitly states that the anisidine value test is not applicable to flavored oils. The global organization for EPA and DHA, also called Goed, are who set these voluntary benchmarks. All this matters because when we look at large market surveys, these testing limitations directly influence how many products appear to fail oxidation standards. When oxidation is evaluated across the U.S. market, more than half of omega-3 supplements exceed at least one voluntary freshness benchmark. In a 2023 multi-year analysis of 72 products sold between 2014 and 2020, 54% failed one or more go-ed oxidation specifications. That tells us oxidation is not a fringe issue, but it doesn't tell us where the problem is concentrated or why it's happening. For that, we have to look deeper at how these products are actually formulated. When the data are broken down by formulation, the pattern becomes more clear. The oxidation failures are overwhelmingly concentrated in flavored products. In this same data set, 68% of flavored supplements exceeded the goed tox limit compared to just 13% of unflavored products, making flavored oils more than five times more likely to fail. This doesn't mean flavored products are inherently unsafe. It reflects a combination of chemical instability and testing limitations, particularly with anisidine value, which we discussed earlier. The point is that oxidation risk is not evenly distributed across the market. Once we see where oxidation failures are concentrated, the next question becomes unavoidable. Do these chemical standards actually correlate with biological harm in humans? In other words, does exceeding a peroxide value, anisidine value, or totox limit meaningfully shift the balance away from the known health benefits of omega-3s and toward real physiological risk? To answer that, we have to move beyond chemistry and market surveys and look directly at what happens in humans. To directly test whether oxidized fish oil causes measurable harm in humans, Otis Stead and colleagues conducted a randomized double-blind controlled trial published in the British Journal of Nutrition in 2012. 54 healthy adults were assigned to consume either fresh fish oil, deliberately oxidized fish oil, or a control oil for seven weeks, all at a high dose of eight grams per day. This design is important. The oxidized oil exceeded common freshness cutoffs. The dose was well above typical supplemental intake, and the study measured established markers of oxidative stress and inflammation. In other words, this trial was designed to answer the exact question that we just asked. The fresh fish oil used in this study had a totalx value of 11 well within industry freshness benchmarks. By contrast, the oxidized fish oil had a totox value of 45. That's about 73% higher than the GoAd voluntary upper limit of a totox of 26. This was not a borderline case. The oil was deliberately and substantially oxidized. That makes the next question important. When humans consume this level of oxidation at a high daily dose, did it translate into measurable biological harm? After seven weeks, the result was straightforward. Despite the high level of oxidation, there was no significant differences between the fresh fish oil, the oxidized oil, and control groups across multiple markers. Markers of oxidative stress, inflammation, antioxidant status, and endogenous antioxidant enzyme activity all remained unchanged. In short, even at oxidation levels well above industry freshness benchmarks, short-term intake did not produce measurable adverse effects in healthy adults after nearly two months of intake. Importantly, oxidation did not impair absorption of omega-3s. Both the fresh and oxidized fish oil group showed nearly identical increases in blood levels of EPA and DHA. In other words, even though the oil was oxidized, the body still absorbed the beneficial fatty acids just as effectively. And this is the paradox. On the market side, more than half of omega-3 supplements fail chemical freshness standards, but on the clinical side, even highly oxidized oil has not shown short-term harm in healthy adults. In other words, chemical quality and observed biological effects do not align as cleanly as people often assume that they do. Importantly, this uncertainty isn't controversial. It's formally acknowledged by the European Food Safety Authority. In its scientific opinion, EFSA concluded that current evidence does not allow oxidation values to be translated into human risk, nor does it support setting health-based limits for peroxide or anistetine values. In short, regulators recognize that oxidation can be measured, but its implications for human harm remain unproven to this point in time. It's also important to be clear about what this study does not answer. The trial lasted seven weeks, so it does not tell us anything about long-term chronic intake. It was conducted in young, healthy adults, which means results may not apply to more vulnerable populations. And finally, the oil was deliberately oxidized in a controlled way. Real-world oxidation may produce different byproducts, at least over longer periods of time. So while the findings are informative, they don't close the book on every possible risk. We don't yet know at what level oxidation of fish oil actually loses health potency or induces harm in humans. Putting this all together, market surveys show that many omega-3 supplements fail voluntary freshness benchmarks, especially flavored products, but this is heavily influenced by how oxidation is measured. Clinical trials, meanwhile, show that even substantially oxidized fish oil does not cause short-term harm and is still absorbed in healthy adults. And from a regulatory standpoint, authorities acknowledge that the human health impact of oxidation remains uncertain and cannot be inferred from chemical cutoffs alone. So the evidence points to a quality and measurement problem and not a proven safety crisis. The takeaway is more nuanced than simply labeling fish oil as rancid or not rancid. Totox is a useful quality signal, but it's an imperfect proxy, not a direct measure of harm, especially in finished flavored products. Severely degraded oils should be avoided for quality and sensory reasons, but when it comes to moderately elevated oxidation values, the evidence does not currently support a clear link to adverse health effects in humans, at least over short durations. True quality assurance means understanding both the limits of our measurement tools and the full context in which these products are made and used. If you care to read some of the primary sources cited in this lecture, you can find them here in the video version of this dialogue. For everybody else, thank you for joining. Until next time. Stay healthy, everyone.