Looks like the old maxim "fat and happy" isn't too far off -- but it's not fat in your body that'll lift your mood.

It's fat in your diet.

We've known for ages that the brain thrives on healthy fats, and now researchers say they can actually see the reaction unfold -- and that the right fatty acids can dramatically raise spirits in minutes.

The researchers recruited 12 healthy, non-obese volunteers and randomly assigned them to get either a solution of fatty acids or saline during a series of mood-altering experiments.

To make sure no one knew whether they were getting the fatty acids or the saline solution, the volunteers were fed via gastric tubes. (Aren't you glad you didn't volunteer for this study?)

The volunteers also had to listen to depressing music and watch images of sad faces, all while connected to functional MRI machines so researchers could watch for changes in brain activity as the experiments unfolded.

The researchers wrote in the Journal of Clinical Investigation that the music and pictures caused moods to dip by an average of 2.5 points on a 10-point scale before anyone was given either solution.

Once those gastric tubes kicked in, however, the volunteers given fatty acids saw a quick rebound -- eventually losing just one point on that 10-point scale.

The saline group, on the other hand, saw no changes.

The MRIs backed up what the patients reported: The music and images altered brain activity by up to 4 percent, which may not sound like much, but actually represents a huge change.

Once again, fatty acids reversed the negative activity, leading to changes in less than one percent of the brain.

Compare that to antidepressant drugs, which can take weeks to work -- if they even work at all (and since most of them barely beat placebos in studies, don't bet your dinner on it).

It's not the first link between fatty food and a good mood. A 1998 study found that a single month of low-fat dieting was enough to boost anger and hostility. Other studies have linked low cholesterol – both in the diet and in the blood -- to depression and even suicide.

Yet the mainstream -- and even the U.S. government -- wants you to get less of those fats?

I'd get angry... but I can't right now. I just had a steak.