That's basically correct; though it's supper that should be given away, actually not 'away', it should be given to enemy. Giving dinner away would be too much. Please, be advised that this proverb is usually told in sarcastic overtone.

>Another (non-existing?) proverb she told me was that one should "eat breakfast alone, share lunch with a friend, give dinner away."
>
>>I have to disappoint you: there is no such proverb in Russian. You idea about diet is closer to truth.