I know that some protein shakes or mass gainers are in a category called “meal replacements,” so does that mean that they’re options to try to get calories when you don’t have many options?

I know it’s kind of a cheat because it’s bypassing the infamous rule of “just eat more,” but that’s not really a big option for me right now.

I get very few calories in a day, so I wanted to know if it’d be possible to use some sort of mass gainer or something to try to get either a “sufficient” amount of calories/nutrients orrrr potentially all that’s needed and more? If it’s possible, does anyone have recommendations for those that aren’t literally like 5000 g of sugar in one serving/scoop?

Also, another quick Q: Is it worth exercising (or even detrimental to exercise) when you don’t eat enough calories?