The 26-year-old star - who lost over 50lbs in 18 months -tried every possible way to lose weight without success, before settling on her current healthy eating and exercise plan.
She said: "I`ve done everything - meal deliveries, milkshakes, diet pills, the juice diet, the maple syrup diet, even not eating at all. I`d do it for three days and if I didn`t feel a drastic change, I`d be like, `F**k this, I`m not doing that anymore.` "
Though she is much happier with her figure, Kelly admits she still sees a therapist about her mental attitudes to her weight and self-image.
She admitted in an interview with Britain`s Cosmopolitan magazine: "I`m in therapy - it`s helped me in all areas of my life. There`s a huge mental factor in losing weight. It`s not just about getting on the treadmill. It`s about doing things to make you feel good about yourself."
Kelly also relies on the support of her mother, TV star Sharon Osbourne, 58, who famously transformed her own shape after having a gastric band fitted.
She added: "Mum`s been so supportive. She understood because she`s been there. When you`re a fat girl in Hollywood, it`s not fun. You never get looked at the way skinny girls do."