Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.

Category: mode of transportation 
Words: bee, swim, fly, car, walk
bee

Category: physical property 
Words: protein, pasty, fat, thin, angular momentum
protein

Category: nutritional value 
Words: salt, fiber, calories, heavy, fat

heavy