Most sources based on medicine (not diet companies) indicate an acceptable rate below kg / week. The highest rate found was 1% of the initial body weight per week. The big secret is not to kill yourself on the road to health - your body is set to make you cope with who you are now - you will have fewer needs and requirements, and you will have to shed a lot of nasty things contained in fat on the way to lower weight.
The lesser secret is to make changes that you can live with over time, learning how to eat right, comes with time, until you make it natural. Most sources indicate that the “throw yourself over a cliff” diet quickly reduces your weight, but you jump as fast - sometimes with collateral damage to gallstones, etc. If you are overweight, you should start your weight loss program with the advice of a medical professional (not a professional diet program employee).
Complex problems may result from medical problems. Treating a symptom (being overweight) without eliminating the underlying problem can be dangerous or pointless.