This is an irregular verb. It follows the conjugation pattern of the verb abrazar.
Present:
Adelgazo fácilmente cuando hago ejercicio regularmente.
I lose weight easily when I exercise regularly.
Preterite:
Con el entrenamiento adecuado, muchos pacientes adelgazan de forma gradual.
With proper training, many patients slim down gradually.
Imperfect:
Cuando era más joven, adelgazaba fácilmente.
When I was younger, I would lose weight easily.