eat like a bird

Fig. to eat only small amounts of food; to peck at one's food. Jane is very slim because she eats like a bird. Bill is trying to lose weight by eating like a bird.

to eat very little We went out for a meal, but she ate like a bird and hardly said a word.

Eat very little, as in Jan is very thin-she eats like a bird. This simile alludes to the mistaken impression that birds don't eat much (they actually do, relative to their size), and dates from the first half of the 1900s. An antonym is eat like a horse, dating from the early 1700s, and alluding to the tendency of horses to eat whatever food is available. For example, I never have enough food for Ellen-she eats like a horse!