A rant is fine but what are you planning to do about the disrespect and laziness of the THREE men in the house who I assume - as I'm sure you'd have mentioned in op if this weren't the case - are fit and healthy at least enough that cleaning and tidying after themselves and planning and cooking meals are all things they are perfectly capable of?!
I suspect you already are kicking yourself for not addressing this many years ago, but there's no reason why it can't be now.
Time for a serious talk with them all and telling them this will not continue. That they are grown ass capable men and need to stop expecting you to be chief cook and bottle washer!
My own dad (NOT the most enlightened at the very least) wouldn't have dreamed of treating my mother or his daughters in this way. Mum did always cook and sort the shopping and meal planning BUT dad always did the dishes (which wasn't just the dishes - and no dishwasher either - but also just generally cleaning and tidying the kitchen inc wiping down all the worktops properly and sweeping and mopping the floor - every evening when he was home [army]) and while they roughly divided chores along gendered lines they certainly were pretty equal in how this worked.
I really don't understand women tolerating such entitlement and laziness. My ex tried it on when we were first married and I pulled him up on it and was backed up by my in laws who had not raised him to be entitled - far from it! He was just trying it on.
Dd who I raised alone was expected to help from a young age and by the time she was a teen was perfectly capable of doing all the basic chores needed to run a home. We divided chores fairly between us based on a number of factors including her having school as her priority and my being disabled and unable to do certain chores.
Op - I think a strategic "strike" would be very useful to you. Prep some things for you to eat (label as food they don't like so they don't take it?) and let them fend for themselves! In ordinary times I'd honestly recommend you disappear for a week or at least a long weekend having run stocks down before your departure so they HAVE to step up.
I think the suggestions of a personal fridge, warming labels and segregated food are all good ideas, you'll know what's likely to be most effective.
I also heartily agree with all the other pps saying they would NOT tolerate this and that you (plural your dh is even more responsible due to his "example" 
) have done yourself no favours raising them to be so entitled and selfish, they didn't become that way by themselves. I pity their future spouses/partners!
I have never done online food shopping in order to leave slots for those who really need them. off topic but thank you for this. I am disabled and housebound and at the start of lockdown it was really hard to get slots and I was seriously worried I'd end up stuck!
Op it's really inexcusable behaviour from an 18 and 21 year old, let alone your dh who must be at least what? 40 something?!
One point though on amount being consumed, teens and young adults do need more cals than adult bodies, my own dd is also very tall and slim (at least partly due to her own disability which means extra height and higher metabolism) she has to eat more than others of her stature as otherwise she would actually lose weight and she's at the lower point of healthy weight anyway. Very hard to get enough cals into her as another feature of her condition is she can't manage large meals in one go, she has to have 5-6 smaller meals spread through the day. It also affects what foods she can eat, I used to think fussiness as she wasn't dx until high school (whole other story) but once we had dx I was surprised to learn the foods she dislikes are not well tolerated by people with her condition. This includes high fat foods so it's been a real challenge finding "tricks" to get enough cals into her to maintain a healthy weight.