IFOS 5-star, explained

Last reviewed July 2026.

IFOS (International Fish Oil Standards) is a third-party fish-oil testing program run by Nutrasource. Unlike a pass/fail seal, IFOS tests each batch and publishes a full numeric certificate, then assigns a star rating up to five. Because the underlying numbers are public, the rating is auditable — you can open the certificate and check the math.

What the stars are built from

An IFOS product report scores several categories, each against the strictest available standard:

• Potency — does the measured EPA/DHA meet the label claim? (Our ranking uses this measured number, not the claim.)
• Purity — PCBs, dioxins and dioxin-like compounds, below strict thresholds.
• Stability / freshness — peroxide, anisidine and TOTOX oxidation values.
• Heavy metals — mercury, lead, arsenic, cadmium.

A 5-star product meets the top tier across these categories for the tested batch. The key phrase is tested batch: ratings are lot-specific and can change batch to batch.

Why "5 stars" isn't the whole story

Most well-made fish oils on the market test at 5 stars — so the rating alone doesn't separate them. Two 5-star products can differ a lot on how much real EPA+DHA you get per dollar and on freshness (TOTOX). That's exactly why our ranking starts from IFOS certification and then sorts by cost-per-gram-of-actual-omega-3 — the star gets you into the room; the math picks the winner.

How to read a real certificate

Each product in our table links its IFOS certificate. Look for the "Batch Results" column next to "Concentration" (the claim): that's the measured value. Check the stability section for TOTOX, and the heavy-metals section for mercury/lead. Note the lot number and expiry — a certificate describes one batch, at one point in time.

"IFOS" and its marks are trademarks of Nutrasource; we cite published certificate data with attribution and claim no affiliation or endorsement.