protein, protean

Protein or protein means the dietary substance, an organic compound found in plants and animals--
If you eat plenty of whole grains and legumes, you should get enough protein to be healthy.
She is tired all the time; it could be a protein deficiency.

Protean or protean means changeable; able to change shape or form--
This amoeba is called protean because it can change its shape.
Proteus was a Greek god of the sea, and could change his shape, so protean now means shape-changing.

Now that you know that, you can say--
"When he goes on a low protein diet, he's like a different person; it's a protean transformation."