What exactly is negative calorie food?
In reality, there’s no food you can find that has negative calorie. They are called negative calorie food is that they contain more nutrients and fewer calories. So digesting such food will take up more food energy in the body than they actually provide.
Hence they haven’t really provided your body with calories, rather you’ve burned calories trying to digest them. This is why such foods are prescribed for weight loss. They are mostly vegetables and fruits.