Are vegetarian and vegan diets really that healthy? I've read somewhere that it was difficult to get enough proteins, which could cause a series of health problems. Plus some of the vegetarian/vegan people who I know take diet supplements like fish oil to make up for the proteins they don't take, so I don't see how refusing to eat fish but then taking those supplements it's beneficial.
It’s definitely possible to be healthy on a vegetarian or vegan diet. I think it’s easy if you’re vegetarian–eggs are fantastic sources of protein and vitamins–and requires a little more planning but isn’t that hard if you’re vegan. There’s a lot of non-meat sources of protein: tofu of course, but also beans, nuts, whole grains, and some vegetables.
I’m not going to go into huge detail because personally I eat meat, and there’s a ton of resources out there about vegetarian/vegan diets, but it definitely can be done.
Fish oil isn’t a protein supplement, by the way–there’s no protein in it, it’s pure lipids–but it provides Omega-3 oils and sometimes Vitamin A. Most people can get enough of those from their regular diet, (including a plant-based one), so it’s sort of uncertain whether it’s necessary to supplement or not.