It's probably this
stupid DIET I'm on.
The Big Bang Theory Season 7, Episode 2
changed her DIET,
and in a few months, she...
The Big Bang Theory Season 7, Episode 16
Why are you on a DIET?
The Big Bang Theory Season 7, Episode 2
"Wil, do you want more Diet Coke?
The Big Bang Theory Season 8, Episode 20
...and their potato-based DIET.
The Big Bang Theory Season 8, Episode 22