Learn Russian: Хорошее питание — это важно, притом нужно помнить про режим. - Good nutrition is important, besides, one needs to remember about the routine.

Both притом and причём are additive conjunctions meaning "besides," "moreover," or "what's more." They add an extra piece of relevant information to what was just said. In this sentence, they are completely interchangeable. If there is a slight nuance, притом emphasizes adding another independent factor (the routine), whereas причём often introduces a clarifying detail about the exact same thing you just mentioned. But here, either works perfectly.

Why is there a dash and the word это before важно? Couldn't we just say Хорошее питание важно?

You could definitely just say Хорошее питание важно, but inserting a dash and это is a very common, natural Russian phrasing. When linking a noun phrase subject (like Хорошее питание) to a short adjective or adverb (like важно), the — это creates a slight conversational pause and adds emphasis, translating roughly to "Good nutrition — that is an important thing."

Why does the sentence use про режим instead of о режиме?

Both mean "about the routine," and with verbs like помнить (to remember), думать (to think), or говорить (to speak), they are functionally interchangeable. However, про followed by the accusative case (про режим) is heavily favored in everyday spoken Russian, whereas о with the prepositional case (о режиме) sounds slightly more formal or literary.