In regards to whether or not fish oil can go 'bad', the answer is yes, fish oil can go 'bad'.
When we talk about 'bad', we usually refer to it as fish oil going rancid. Fish oil products, more than most other supplements, vary widely in their quality. Low quality fish oils can have a bad fishy smell, cause intestinal distress and often have but a fraction of the benefits of a good quality omega fatty acid. High quality fish oils tend not to have a bad smell to them, are well tolerated and are fortified with antioxidants, to eliminate oxygen and the chance of oxidation. We always recommend taking high quality fish oils from reputable manufacturers.
The key to fish oil freshness is to protect it from oxygen. When exposed to oxygen, fish oil becomes oxidized (which changes the molecular structure) and becomes rancid. Well preserved fish oil rarely has a fishy smell or taste. If it does, there is a good chance that it has been exposed to oxygen and is becoming rancid. Consuming rancid fish oils should be avoided, as they provide less health benefits and can cause intestinal side effects.
What Makes Fish Oil Go Bad?
So what makes fish oil go rancid? As we mentioned above, it is exposure to oxygen that makes fish oil go rancid and there are multiple factors that influence how much oxygen the fish oil is exposed to including:
- The manufacturing process
- How the fish oil is packaged
- Dosage form of the fish oil (capsule, enteric coating etc...)
- Storage conditions
- Purification process
In general, fish oil should be stored in a cool dry place and be kept away from extreme heat. This is not only to protect the actual fish oil, but also the integrity of the capsules, softgels etc... Heat, while in itself does not cause oxidation, greatly speeds up the process, especially if the manufactured fish oil isn't of high quality and contains small amounts of oxygen. With high quality fish oils, there is no oxidation to speed up. High quality fish oils can often be handled and stored at hot temperatures and not be affected.
It's difficult to say if your specific fish oil product is damaged or not as we are not overly familiar with that product from that manufacturer. Heat will most certainly affect the integrity of the capsules as you mentioned, but the actual fish oil may be OK. If it is overly fishy smelling or if you are having bad effects from it, it may be rancid and we would recommend getting a replacement product.
It is worth mentioning that even high quality fish oils may produce negative intestinal effects as some people may not manufacture enough of a fat digesting enzyme known as lipase. If you haven't taken fish oils ever before, or if it has been some time, it often takes time for your body to become used to taking higher amounts of fats. We recommend that you take fish oil with food as that can help gastrointestinal issues that may arise.