What would cause a man in his mid-to-late 60's have issues with his sense of taste?

This man is working with his doctor and has an appointment with a neurologist (I think that’s the type of doctor he said) to try to discover the cause. And, hopefully, how to fix it. He has had a brain scan that showed no tumors or obvious problems. His most recent blood work – including thyroid – came back normal.

This problem is rather odd. He had always enjoyed most foods, a few dislikes but no more than the average person. He can’t seem to put a pattern to what tastes good and what doesn’t. Below I’ve listed the things that I remember he has said:

Still good: most fruit, pork chops, spinach, bacon, ice cream, milk shakes, black coffee (although he says that seems a bit more bitter of late), blue cheese dressing

Not good: bread, crackers, pretzels, cheese

If I remember correctly, burgers, steak, chicken and chocolate are on the list of things he likes but no longer have taste appeal. They don’t taste bad, but they don’t taste good. I don’t remember where he is with spicy food. I know he likes it, but I don’t remember if it still tastes good to him.

When we first started talking about this, my first thought was that it was aging related. But to me, it seems like there could be more to it. This has been going on over the last six to eight months.

He is really tired of this and I’m hoping that there are some jellies with a bit of insight. Thank you!