Back to fish + chicken?

It has been now more than a year since I totally stopped buying fish.

Chicken was already gone maybe one year before that.

Now, over the last year, I noticed as well a renewed weakening or slight pain on lower back and sometimes knees.

It is not much but is enough to ring an alarm bell.

Is this related with a lack of protein?

This is one of the key questions I have right now.

If protein stimulates muscle building and muscle sustains knees and back, then lower protein intake will negatively impact on the muscle mass.

therefore, it might weaken these joint and lower back areas.

Is this true?

Is this how it works?

This is a theory I would need to confirm