Let's say we have an item of food that contains 500 joules of energy. And let's say that our body expends 40 joules of energy to digest it. So the total gain from eating this piece of food is 460 joules.
If we could create food that costs more energy to digest than is in the food, then people can eat more and more and more of this food to get skinnier and skinnier and skinnier.
Now I know we have matter and antimatter but I don't think swallowing antimatter will help here. But what might help is chiral mirror-image molecules of food that we regularly eat (for example left-handed sucrose instead of right-handed sucrose).
The idea is that our body would waste energy digesting these foods and not actually gain any energy from them. So we would burn fat by stuffing our faces with food.
Of course it might be tricky to get this antifood to taste nice.
If this becomes a reality in 2050, you know it was Kimbo who came up with in 2021.