> That, said, I've tried going vegetarian multiple times before and honestly I felt awful - I'm naturally very slim and not particularly energetic to begin with, and when I was on a vegetarian diet I felt totally lethargic.

The same thing happened to me when I first tried going vegan. It wasn’t until I went through a major effort at planning my meals — to the point of making an outright diet plan for myself — that I was able to make veganism work for me.

From your description, it sounds like you were eating too little calories.

Could also have been b12 or iron.

You're right about meal planning. I also think that if you're going to cut out an entire food group you should phase it out. You eat food every single day. You have to find something that works long term for you.

A key thing is that some folks have boring "meat and potatoes" taste, with no interest in moving beyond that. My parents are old-timers living in the Irish countryside. When I was growing up in the early 80s, you couldn't get one-tenth the stuff I now eat a daily basis. I became a vegetarian by first developing a love for cooking (especially Indian). When you have a wide range of tastes, and the supermarkets stock everything you need, it's easy to find alternative to meat. Otherwise, it takes a long time to expand your tastes and learn what to actually do with ingredients. My mother walks around the supermarket at the weekend, and still picks up the same old things she used to get in the 80s. She wouldn't know what to do with 90% of the herbs and spices on my shelf. So asking her to cut out the one tasty part of her daily meal is pointless, not to mention unhealthy (she would have low b12 and iron).

If I were a meat eater planning to go vegetarian I would avoid cold turkey (not a pun). Phase it out. Maybe start with the biggest greenhouse emitters (cow), or the most intelligent (pig). Maybe give up fowl and fish last. Rather than see it as a limitation, start by learning how to cook one new meal every week that is nutritious, tasty and also meat free. Also, if someone else is doing all the hard work (ie: you're in a restaurant or ordering delivery) use that as an opportunity to try different things that don't have meat. Indian food is great for this because it's not just "meat and potatoes without the meat" or their vegetarian food is amazing. But you might need to develop a taste for it.

For some people it might take a year, but if you think about it as expanding your tastes, perhaps it won't feel like a chore, and you won't feel like you've given up anything (especially now that you can fall back on the decent meatless burgers/sausage you can get nowadays).

It's funny to me how people talk about iron being a problem on a vegetarian diet. I've been a vegetarian for a decade or so now and my iron level is consistently at the very high end of the normal range. I don't do anything special to achieve this.

Same. I'm a vegetarian and I'm in perfect health. But if someone is extremely lethargic all the time, it's usually either iron, B12 or calories (rarely the latter). Also, some people become vegetarian and simply do it wrong. I know a girl who is vegetarian for icky reasons, ie she is disgusted by the idea of eating something's spleen/veins/anus, and it just stops her from eating any meat. But she's similarly icky about vegetables. Hates all kinds of things. She's low on iron, is constantly sick and lethargic.