Who has lost any weight by doing Kapalbhati Pranayam? How much time did you invest in doing the pranayama per day?
Kapalbhati Pranayam can be quite effective at losing weight. Usually you will do around 20 breaths for 1 cycle, and each breath may vary in duration between 10–15s.
If you are just starting off, you can do 1 cycle of 20 breaths, but you can add more and more cycles as you go.
Regular practice of Kapalbhati not only helps with weight loss, but it also promotes better blood flow, digestion, and also helps with maintaining focus.