Cleaning fish oil with heat and chemicals makes it last longer without going rancid, even though it loses some natural antioxidants.
Scientific Claim
The four-stage chemical refining process (degumming, neutralization, bleaching, deodorization) increases oxidative stability of fish by-product oils at 80°C, 100°C, and 120°C, as measured by induction period in the Rancimat test, despite reducing natural tocopherol content by 31–45%.
Original Statement
“The refinement process prolonged the oil oxidative stability in all cases... The tocopherol content of oils from farmed fish species is higher in comparison to oils from wild fish... however this content did not enhance its oxidative stability at elevated temperatures.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
Oxidative stability was measured directly via Rancimat under controlled, standardized conditions (20 L/h airflow, 80–120°C). The definitive verb 'increases' is appropriate because the effect is quantified and statistically significant.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized Controlled TrialLevel 1bWhether refined fish by-product oil maintains oxidative stability in real-world storage (e.g., in supplements or food products) over 6–12 months.
Whether refined fish by-product oil maintains oxidative stability in real-world storage (e.g., in supplements or food products) over 6–12 months.
What This Would Prove
Whether refined fish by-product oil maintains oxidative stability in real-world storage (e.g., in supplements or food products) over 6–12 months.
Ideal Study Design
Double-blind RCT storing 100 samples of refined tuna by-product oil and cod liver oil under accelerated conditions (40°C, 75% RH) for 12 months, measuring PV, TOTOX, and headspace volatiles monthly, with n=20 per group.
Limitation: Does not reflect ambient storage or consumer use patterns.
Prospective Cohort StudyLevel 2bWhether oils with higher refined stability correlate with lower consumer-reported rancidity in commercial products.
Whether oils with higher refined stability correlate with lower consumer-reported rancidity in commercial products.
What This Would Prove
Whether oils with higher refined stability correlate with lower consumer-reported rancidity in commercial products.
Ideal Study Design
Prospective cohort tracking 500 consumers using fish oil supplements made from refined by-product oils vs. conventional oils, recording rancidity complaints, shelf-life, and return rates over 18 months.
Limitation: Subjective reporting and confounding by packaging and storage conditions.
In Vitro Chemical AnalysisLevel 4In EvidenceThe relative oxidative stability of oils under controlled heat stress.
The relative oxidative stability of oils under controlled heat stress.
What This Would Prove
The relative oxidative stability of oils under controlled heat stress.
Ideal Study Design
The current study design — Rancimat testing at 80, 100, 120°C with induction period measurement — is the ideal in vitro evidence for this claim.
Limitation: Cannot predict real-world shelf-life or consumer perception.
Evidence from Studies
Supporting (1)
Production and Refinement of Omega-3 Rich Oils from Processing By-Products of Farmed Fish Species
Even though the refining process removes some natural protective compounds from fish oil, it still makes the oil last longer without going bad at high temperatures — which is exactly what the claim says.