You actually do need it. The funny thing about nouns in English is that if you don't nail them down, they float about in a very non-committal way. This is fine if you're speaking generally but for singular countable nouns you do need an article, possessive pronoun, number, etc to "mark" it... we call these "determiners".
"Taking a walk after meal" is so vague that the sentence is broken. "Helps" is still the better choice, but if you want a synonym it should be "assists".