Why your fish oil started tasting fishy after 6 months

You opened the same bottle of fish oil you've taken for six months. Today, the burps repeat for hours. They taste worse than before. What changed?

Three possibilities

The oil is doing one of three things — and each has a different action:

1. The oil oxidised in the bottle

Fish oil oxidises from exposure to air, light, and heat. Even an unopened capsule slowly degrades. Once you open the bottle and start pulling capsules out one at a time, the remaining ones sit in increasingly oxygenated air.

By month 5-6, a bottle that tested at Totox 8 when manufactured may now be at Totox 20 or higher. The burps are the smell of that change.

What to do: throw out the bottle. Yes, even with capsules left. Continuing to take rancid oil is observed to associate with oxidative stress markers — the opposite of what you wanted.

2. The oil was never that fresh to begin with

Some brands rely on the gelatin shell to mask the smell. The capsule itself doesn't reveal what's inside until it dissolves in your stomach. By the time you're tasting it, you've already absorbed whatever was there.

The first 1-2 months you may have noticed nothing. By month 3-6, your body's tolerance for the slow drip of oxidation may have shifted, and now the burps are louder.

What to do: check the brand's Certificate of Analysis for the specific batch. If they won't provide one, that's your answer.

3. Your storage habits

Where do you keep the bottle? On the kitchen counter near the stove? In the bathroom? In the car? Fish oil hates heat, light, and humidity. A bottle stored badly degrades 3-5× faster.

What to do: refrigerate. Keep tightly closed. Out of direct light. Never in the bathroom.

The freshness test you can do yourself

1. Bite open one capsule
2. The oil should taste mildly fishy, slightly sweet, or like lemon if flavoured
3. If it tastes sharp, bitter, paint-like, or aggressively fishy — it's oxidised
4. Don't swallow that batch

What I'd do differently next time

• Buy smaller bottles (30-day supply) — finish before oxidation accelerates
• Refrigerate from day one
• Prefer brands that publish Totox per batch on their website
• Prefer brands that include antioxidants (vitamin E, rosemary extract) in the formulation

The burp isn't an inconvenience. It's a sensor. Your body is telling you what your supplement label refuses to. The question is whether you listen.