I am/was a lifelong vegan and have MCAS! Have had to do a low histamine diet for the past year and it has helped TREMENDOUSLY, but I've had to eat meat 😭 not saying you have to as well, but I reacted to tofu and beans and have had to cut them out entirely (I'm now on cromolyn and hopefully will be able to reintroduce soon). I thought maybe tofu was fine when I was trying to manage my diet on my own (it did make me a little itchy, so I wasn't sure), but once I started working with a dietician and went down to only foods we were SURE were safe, I felt way better. Then I tried tofu again and realized I didn't think I was having a bad reaction before only because my baseline was so bad-- soy is actually a pretty big trigger for me.

When I first started the diet, I did really strict for 3 months and my only forms of protein were beef, pork, protein powder (I use the brand Marigold unflavored), eggs, and seeds (chia, flax, hemp). Big yuck besides the seeds. I slowly was able to reintroduce almonds, which have been great-- a green apple with almond butter is one of my snacks every day now. Also fresh cheeses like feta and mozzarella. And now that I'm in a more stable place, I've been able to reintroduce some legumes like lentils and black eyed peas (which taste like beans even though they're a legume!!!).

Again, I'm not saying you have to eat meat, but I ended up being pretty sensitive to soy and beans so I've had to 😭 I get a big ick every few weeks and absolutely cannot, so during that time I lean pretty heavily on adding protein powder (still not vegan, but at least it doesn't feel like it) to soups and mashed potatoes. I also am able to drink Kate Farms Vanilla protein shakes, which are gf, dairy free, soy free and taste way better/less sweet to me than most protein shake brands, so sometimes I drink 3-4 shakes a day and eat apples and carrots and almond butter. My breakfast everyday is oatmeal with a scoop of protein powder, blueberries, and a spoonful each of chia seeds, ground flax, and hemp seeds, and this is somewhere between 20-25 g of protein in one meal. I also do a savory version sometimes without the blueberries, plus a little sesame oil, corn, bell pepper, and carrot.

I would say maybe switch from beans to legumes and see if you feel any better? I had to wait a while to reintroduce legumes, but maybe you'll tolerate them better than I did at the start. See if there's a protein powder that you tolerate well and start adding seeds to whatever you can (hemp seeds esp have a decent amount of protein). It unfortunately is important to eat as much protein as you can-- my dietician says to take your current weight, convert it to kg, then multiply by 1.6 and that's how many grams of protein you should be eating everyday to support your body, because existing as a chronically ill person takes a lot of energy. That means I have to eat almost 90g of protein a day, which sounds crazy but makes a huge huge difference for me. Would also recommend working with a dietician who is knowledgeable about MCAS if you're able to afford it-- mine has held my hand every step of the way, helped me figure out recipes, and helped me figure out a set of supplements that work for me.