Custard, you have my sympathies. I am in a very similar situation with my DH.
He's put on five stone in the last three years. His BMI is now 30, so "obese". He is wrecking his health. The weight gain has given him a fatty liver, as well as sinus problems, sleep problems, back problems ... but he still clears out the fridge and cupboards.
My grocery bills are over £100 a week for two adults, and that does not include alcohol, desserts or snacky things (neither of us drink, so I can't even blame beer for it).
To top it all off, the situation is getting worse and, like you, I do not know what to do about it.
I will come down in a morning to find huge amounts of food have vanished from the fridge. Big blocks of cheese will go in about two days. Boxes of crackers last a day. Any cooked meat just disappears. I will roast a reasonable-sized beef joint at the weekend with the idea that it will do for lunch through the week after the meal, and it will be gone by Monday evening. I've known him to consume two tubs of taramasalata in a couple of days and a fortnight ago, I opened a 750g tub of peanut butter that I had bought the week before to find it empty -- there was something like 3000 calories in that tub and he had eaten the lot at the same time as having eggs for breakfast, a cooked lunch and a proper dinner at night.
In the past, I've bulk-cooked lasagne or moussaka, and he has eaten eat three large family-sized dishes in a day and a half. He once ate an entire stewpot full of bolognaise sauce made from one kilo of mince in twelve hours. I made it during the afternoon to freeze in portions; when I got up the next morning, the pan was empty.
And, like your experience, he is actually screwing up my nutritional needs because when I shop, I think about meals and food groups and different types of protein so that we get a balanced diet, but before I know it ... all the fish has been eaten, all the cheese has gone, he has fried up the chicken and eaten it (he ate over a kilo of chicken in 24 hours a few weeks ago). I have been left with just toast or white rice on many occasion.
And I hate to say it, but there has been a bit of gaslighting over the issue in the past. It wasn't until I started tracking where food was going that I realised just how much he was eating in a week.
There are a few causes that I have identified ... whether they will help you, I don't know.
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My DH works from home so makes meals during the day himself and obviously has the opportunity to snack.
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He eats stupidly fast, and he was trained to do this by his mother's rushing to finish meal times when he was young.
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The problem seemed to accelerate when he started buying and drinking iced coffee drinks. They are full of sugar and I think they screwed his system up somehow.
I have done everything I can to support and help him tackle the problem. You would think that an ultra-sound scan showing the fat in his liver would shake him into action, but it hasn't.
God knows where it will end up. 