Hi Diego. If you find the leaves eaten in salads and cabbage, the causes can be different, the most likely are two: caterpillars or snails.
Counteract the caterpillars
If they are larvae caterpillars you will find small holes on the leaves and perhaps you can see the small larvae if you look for them inside the clump. To intervene in this case I suggest you use the bacillus thuringiensis, completely non-toxic and natural product.
Counteract the slugs
If they are snails and slugs, on the other hand, you will see the "bites" of larger dimensions, generally starting from the outside of the leaves. Snails are very voracious, if you say that they leave you only the stem, these gastropods are probably responsible for your problem. You can defend yourself in various ways: by scattering ashes or coffee grounds, or by realizing traps with beer. The last resort is the use of snail killers, there are also organic ones and I advise you to use special dispensers such as trap file. I think you might find it useful to read the article dedicated to defense of the garden from snails.
I hope I was helpful, a warm greeting and good crops!