"The rice and pasta"
"le" and "un" and "les" and "des" are not interchangeable. In both English and French language, their use is defined by rules which are not always similar.
DEFINITE ARTICLE "the" => le, la, les
As their name explicits, they define nouns: the meal = le repas, is a specific meal, not any meal. Often, when you get longer sentences or a full text, you get hints by context.
- ex: the woman eats THE rice that the cook prepared = la femme mange LE riz que le chef a préparé.
Note1: in English, when you claim a generality, like "men are stronger than women", the French use the definite article: "LES hommes sont plus forts que LES femmes". The same goes for "LE riz et LES pâtes".
INDEFINITE ARTICLE "a/an" => un, une, des
In this case, the object is not defined, it is rather "one" thing out of several. - ex: the woman eats A banana = la femme mange UNE banane.
Note2: in English, "a/an" has no plural, whereas in French, the plural of UN/UNE is DES.
- ex: the woman eats bananas = la femme mange DES bananes (= a certain quantity of)
In this case le riz/ the rice would lead one to think it would also be les pâtes/ the pasta. Had it started by talking about some rice..du riz then I would have continued on to des pâtes.
Your statement Le riz et des pâtes would translate as The rice and some pasta. While grammatically correct it would imply something special about the rice but not the pasta.