About 5 years ago I stopped eating gluten. For me it was mostly some intolerance and skin reaction. Needless to say how well I am doing now compared to before. Finding the link was the hard part and took decades.

A side effect I noticed was the disappearance of allergies. I had some level of pollen allergies and can't recall to have any reactions anymore, which is part of having a improved immune system function.

This is where it gets interesting to that article. I also noticed my general far better mood stability. I never had much of a problem, but like any human some ups and downs. Being more energetic I recognized also that I am far more upbeat. I do have no real explanation and it is only my case, but I can see the link between the digestion and depression.