Start with EPA and DHA, not "fish oil"
A bottle may say "1,000 mg fish oil" in big print. That number is the weight of the oil, not the weight of the omega-3s inside it. The omega-3s that most buyers care about are EPA and DHA. Look for them by name in the Supplement Facts panel, and read the amount for each one.
The rules for that panel are in federal law, 21 CFR 101.36. The panel must show a serving size, such as "2 softgels." The amounts are listed under the heading "Amount Per Serving." The rule also says the amount shown should be the weight of the ingredient itself, not the weight of its source. That is why EPA and DHA should have their own lines. If a label lists only the total oil, you cannot tell how much EPA and DHA you are buying.
Check the serving size next. Some bottles show amounts for two or three capsules. If you compare brands, compare the same amount of EPA plus DHA, not the same number of capsules.
Know the oil form
Fish oil comes in more than one chemical form. The GOED voluntary monograph, a quality standard from the Global Organization for EPA and DHA Omega-3s, covers oils sold as triglycerides, re-esterified triglycerides, or ethyl esters. The form is often printed in the ingredient line or the product name. It does not make a bottle good or bad by itself. It does tell you what you are buying, and a clear label names it.
The same monograph says the EPA and DHA content should be given as milligrams per gram of oil. It also lists other oils in its scope, such as cod liver oil, tuna oil, salmon oil and green-lipped mussel oil. Cod liver oil is a different product from a concentrated fish oil, so read the name on the front and the ingredient line on the back.
What freshness tests mean
Fish oil can go rancid. Oxygen breaks down the fats, and the oil starts to smell and taste off. Labs measure this with a few simple tests, and most labels do not print them. A certificate of analysis or a company web page often does.
- Peroxide value (PV) shows early damage. GOED sets a maximum of 5 meq/kg.
- p-Anisidine value (pAV) shows later damage. GOED sets a maximum of 20.
- TOTOX combines the two. It is (2 x PV) + pAV, and GOED sets a maximum of 26.
Lower numbers mean fresher oil. The monograph notes that the anisidine and TOTOX limits do not apply to flavored oils, because flavors interfere with the anisidine method. So a lemon-flavored oil may show only a peroxide value. That is not a red flag by itself.
The limits are tighter than those of some official books. The 2017 New Zealand study below notes that the European and British Pharmacopeias and Australian authorities use looser limits, including a peroxide value of 10 meq/kg.
Dates and storage on the bottle
Look for a lot number and a best-by or expiry date. The GOED monograph says its limits apply through the stated shelf life of the product. So a freshness claim only helps if the date on the bottle is still ahead of you. A sealed bottle that is past its date is a poor buy, whatever the limits say.
When you open a bottle, a strong sour or sharp smell is a sign the oil may have gone off. Store it as the label says, and keep the cap tight.
Seals, standards and lab names
Be careful with the word "certified." The GOED monograph is a voluntary standard. It is not a government approval, and it is not a seal. A company can say its oil meets it, so ask to see the lab report. A sound outside lab holds a recognized accreditation, such as ISO/IEC 17025, and uses validated methods. A lab report that names the lab and the method is stronger than a logo.
Third-party testing programs also exist. They buy or sample products and publish results. The study below shows why that matters. Researchers published a study of 47 fish oil products on the New Zealand market in 2017. They found that 91 percent met their EPA and DHA label claims. They also found that 72 percent met the voluntary peroxide limit, 86 percent met the anisidine limit and 77 percent met the TOTOX limit. Most products passed. A sizable minority did not, and no label could have told you which ones.
One more point: the study notes that an earlier report on the same market found far lower compliance. Testing results can differ by method and by lab. Treat any single test as a snapshot, not a final word.
A quick checklist
- EPA and DHA are listed by name, with an amount for each.
- The serving size matches the amount you plan to compare.
- The oil form is named, such as triglyceride or ethyl ester.
- A lot number and best-by date are printed.
- The company can show a lab report with PV, pAV and TOTOX, or says the oil is flavored.
- The lab is named and accredited, and the standard is described as voluntary.
One limit applies to all of this. A label and a lab report describe a batch at the time it was tested. Heat and light after that can change the oil. This guide covers how to read a label. It is not advice about what you should take.