Being poor is kinda a messed up way to become fat. Unless you, like, don't have any money for food, your only option is the cheapest, unhealthiest processed food. Eating healthy costs a lot of money.
man I hate this kind of misconception, but it's not your fault. For some reason there's a Mandela Effect of someone professional claiming this is true and now everyone is sticking to it... Really hurts as someone raised by a dietician seeing this being said all the time.
rice and chicken are two of the cheapest foods in the world, and neither are particularly fattening. Spinach is a super food (you literally burn more calories digesting it than you get from eating it) and it is the cheapest can of vegetable that you can purchase. As sweet as they are, carrots are actually quite healthy too.
You can lose weight just by eating those and drinking normal non-sugary drinks + doing standard exercise for weight loss. The actual problem is that it's boring. I'm guessing the "Weight loss foods" you're referring to are stuff like "Lean Cuisine" and such...those are designed to taste just as good as the variety of fattening foods out there while costing few calories, that's why they're expensive. Also they aren't all that effective, to be honest.
Speaking of fattening, if more people had a clue what was actually giving them problems there'd be a lot less confusion.
Common fat traps people normally have no clue about: Literally any carbs(pasta, ramen, breaded foods), cereal(most are LOADED with sugar, plain Cheerios or don't eat it), literally any soda, doesn't matter if it's 'Diet" or "zero sugar", it's the salt that's screwing you up actually, sliced meats(LOADED with salt), fruit juice (sadly yes they are sugar bombs), ranch dressing (if you can't use a literal tablespoon of it as the entire serving, just quit cold turkey), all candy, all pastries/snack foods, chips. Don't even think about fast food. lol I could go on and on, if you aren't cooking it yourself there's a good chance it's a calorie bomb or a salt bomb.
If anything, the hardest part about losing weight is the sheer amount of misinformation about it. People think they SHOULD be losing weight when in reality they are sabotaging themselves.