Gaining

because the issue is usually a matter of stomach capacity, the best way to increase your capacity, is to get yourself a blender. a good one, like a vitamix/blendtech/etc.. fill it with whatever you want, doesnt matter as long as its good enough for you to drink a lot of. fill the blender to about 90% capacity, blend it up and drink whatever it is within a half hours worth of time. do this 4 times a week. my favorite thing to blend is fairly healthy: a whole lemon, cucumber, handful of sauerkrait, raw ginger and turmeric with water and ice. tastes like a cold soup, and is very healthy, but most importantly, there's a LOT of it, and I can drink it down without any issues. if you make an easy to drink shake about 4 times a week and drink them within a half hour of making them, you will put on weight. not from the shakes, but from an increased capacity, so when you do sit down to eat, you can eat a ton. After a while, when your stomach is used to drinking and eating a ton, you can switch up the ingredients to be more calorie dense. try this, you will be pleasantly surprised

Capacity is not necessarily an issue. Sure, it can help. But you can achieve the same thing with smaller, more frequent meals.

Grazing is very effective in this regard. You end up eating a shit load of calories because you never felt full.

To be clear, there is nothing wrong with your method. I'm just mentioning this as well for accessibility reasons. Shit's expensive these days, and it's cheaper to fatten up with bulk snacks.

I hope that you are seeing an immunologist for what appears to be a severe allergy to nuance.

Also, who in the world is buying second-hand equipment to improve their capacity? What equipment are they even using? Please, make it make sense.

Sure, you can get fatter faster by eating a shit ton of food, but that's putting your wallet on a diet. It's not necessarily expensive to stretch out your stomach, but it gets extremely expensive once your appetite increases. And how are you going to maintain your food expenses when you don't have money to buy food? Now you gotta eat less while dealing with hunger pains on top of all of that.

You might have been in this community longer than I have, but that doesn't make you above people adding to what you've said. You don't know and cannot know everything. Hell, I have formal education on my side, and people who do not have my background add really good points to things I say all the time.

It's not that deep, beloved.

To circle back to the OP question. You need to add an extra 500 to 1000 calories per day (depending on how active you are, your metabolism etc.) to gain one pound per week (roughly). Honestly, it doesn’t take a lot to do that imo. If you’re not lactose intolerant, a 32 oz carton of heavy cream at Walmart is about $6 and contains roughly 3000k of calories. Don’t chug it all at once but add it daily to your coffee, cereal, Mac n cheese or anything else that you use milk for. So for very little money and very little extra food volume, you’ve covered most of your extra calories.