This is not to say that if you don't get enough omega-3s that you will get mentally ill, but there appears to be a real link. Many factors contribute to mental illness, including, genetics, chronic stressful experiences, physical activity and yes, diet. Omega-3s look like they are one piece in the puzzle.

What about Mercury?

So should you just eat more fish? This brings up another problem. Too much fish can lead to problems from mercury and PCBs. In fact, pregnant women are advised not to eat fish at all. This is a big debate in the medical community because omega-3s are incredibly important for development of the fetus and the growing baby will ‘steal' omega-3s from the mother if she doesn't get enough in her diet. Some researchers argue that this advice does more harm than good. Still, most doctors today don't offer their pregnant patients any other alternatives – they just say don't eat fish.

This is where fish oil supplements can come in. They are becoming very popular and offer a safe alternative – if you are careful. The thing to look for is ‘molecular distillation' on the back of the bottle. This means that the manufacturer has tried to remove heavy metals and PCBs. Still, I would check with them to make sure they have some kind of quality control since the FDA does not regulate this claim.

Why now?

So why didn't we have all these problems centuries ago. It's not like all our ancestors took fish oil pills all the time. Well, there is another major factor that I haven't mentioned yet – omega-6s.

Omega-6s are another kind of PUFA that are also important in the brain. The balance between omega-6s and omega-3s in the diet is very important. They are like the yin and yang of fats. They compete with each other for many biological functions and keep each other in check.

For example, omega-6s help the immune system by turning on inflammatory processes necessary to fight infections. Omega-3s help to turn it off and keep inflammation low. They are both important but need to be kept in balance.