The best performing diet that has published research is low carbohydrate or keto.

That means avoiding high sugar and high starch foods like bread, pasta, potato, fruit, juices, processed food

The best description I have seen is nothing made of wheat, rice, grain, no vegetables that grow underground, no pumpkin, no fruit, as much meat, seafood, fat as you like.

The current health advice is to avoid canola and vegetable oils as they do specific metabolic damage. The safe plant based fats are coconut and avocado. All animal fats are safe.

The odd thing about this diet is you can eat fat and get thin, but it makes sense in that it trains your body to burn fat, which is what you want!

Dr Ken Berry on YouTube has good advice about starting such a diet.