Definite and indefinite articles usage

Question

I have real problems with when to use articles. In this exercise why fruta Y verdura (no articles) but la piel y el rendimiento (articles)?Thanks for any advice

Answer

Hola Maggi,I find the Spanish articles at the following website helpful:https://www.thoughtco.com/use-and-omission-of-definite-article-3078144You can just copy & paste the above into your search engine. There are a few articles on the usage and omission of definite articles. Hope this helps Clara :)

Answer

Hola Maggi
The use or omission of the articles is something that creates a bit of frustration to students are there is no clear rule about when exactly to use them and when not. We do have a few lessons on specific scenarios when you really need them but other than that I can only say that when we omit the definite articles (el, la, los, las) it is because we see those nouns in a very generic way, without wanting to be specific. We do use them when we are referring to something a bit more specifically. For example, in this writing exercise we are omitting the article to say: 
She eats fruits and vegetables
We mean fruits and vegetables in general.
When it says:
It improves skin and athletic performance
we use the articles:
Mejora la piel y el rendimiento atlético
Here we see these direct objects as more specific things.
I'm afraid there is nothing written about this where there is a clear answer to this issue.  (I keep looking myself) It is one of the things that are more difficult to master in Spanish. 
Saludos