Upvote:1
The voice is a "wind-instrument" and it relies on resonance. We have different cavities in the body, e.g. the nasal cavity and the chest cavity. These cavities are where the sound vibrations resonate and thereby gain frequency, e.g. low or high frequency.
When there is tension in the body, i.e. in muscles and ligaments there is restriction and contraction creating less space for the sound vibrations to resonate in. Sound vibrations love more space and tension kills them. Relaxation is important in order to create rich sound vibrations. A lowering of the voice can take place if there is a "bigger" cavity to resonate in, due to less tension in the body, thereby giving the vibrations a larger range of frequency to resonate in.
Its difficult to answer whether or not vegetarianism plays a role in your voice changing. There are many factors involved. You could try asking the question on the other SE's, e.g. "Health and Biology" to gain more answers or ask your doctor for a strictly medical answer if thats what your looking for. I would say get a lot of different opinions on it instead of limiting yourself to one perspective. Then you can evaluate the different answers you got and find out which one fits the best.
From a buddhist perspective an answer will be that your voice changes because it belongs to the 5 aggregates, i.e. the 1st aggregate of form. These aggregates are subject to the 3 signs of existence and therefore they are unstable, in a constant flux and ever-changing.
Upvote:4
It's probably to do with the absence of tension. When you're relaxed, your voice tends to be lower. If you meditate or do yoga the voice naturaly goes in that direction. It's possible something similar happens when you eat very healthy and remove other kinds of tensions.