Strict fast for us meant abstaining from meat, dairy, eggs, fish, olive oil, and alcohol. On certain "feast days" you could have fish and/or olive oil and beer/wine. It took quite a bit of discipline to do this. Many people made vegan desserts, but that's kind of cheating. You could also eat shellfish, just not fish.
Here you couldn't eat meat on Fridays, if you were catholic. So you ate fish (apparently vegetarian/vegan was not an option). You could eat beaver, water rat or ducks, though. Because they swim, they were considered 'fish'...
I can't help but think there was some farming-related reasoning behind abstaining from some of these foods, too.
Could be you are referring to the 'hungry gap'. From winter to early spring there's not much vegetables to harvest; those months are the hungry gap. Around Easter more and more vegetables become avaiable, chicken start to lay (more) eggs, and lambs are born.