Ever since he began cultivating, Lex had a complicated relationship with food. At first, he was extremely reluctant about the fact that slowly he would lose his sense of hunger as his body gained the ability to make do without it. His love for food caused him a great amount of pain when he thought about the fact that he might lose his taste for it.
Not that he would ever dislike food, but that heightened experience of having great food when he was really hungry would surely be something he lost.
But no matter how reluctant he was, it was a bitter reality. Over time, as he became busier, he had less and less time to eat. In fact, as of late, days would go by without him realizing he hadn't eaten since his body wouldn't really remind him, and he would be otherwise occupied.