What is the best diet to loose weight fast?

No answer. It is not a good idea to aim for losing weight fast. A balanced diet rich in fresh vegetables, and fruits and whole grains, low in fats and alcohol would help. Increasing physical activity will facilitate weight loss. The speed of weight loss depends on the degree of caloric restriction. Aim for losing about a pound a week.
Eat fewer calories! Helpful weight loss diets include natural foods that take time to chew but contain few calories. Examples include carrots, celery, and iceberg lettuce (without salad dressing). When shopping for fruits, buy small ones no bigger than a tennis ball, because fruits contain natural sugar. Drinks without calories include water and green tea. A calorie is a calorie, regardless of where it comes from.