You can lose 5 kg in one week but only temporarily, deceptively, and dangerously.
It will be Temporarily:
Because whatever you do to lose the weight will not be a lifelong habit so you can expect all the weight you lose to come back… And then some, as it tends to happen. Research shows that these temporary bouts of weight loss aren’t just ineffective but actually detrimental in your attempt to lose weight: the more a person yo-yo’s their weight the less successful they become at controlling their weight.
Because in a matter of 7 days your body will mobilize water and your glycogen stores as well as muscle and it will tend to retain fat. So whatever weight you manage to lose will be of exactly the wrong stuff that you won’t want to lose.
Because losing that amount of weight in a week will stress your organs with no benefit to them. Depending on the method you will risk serious dehydration, electrolyte imbalances (hyponatremia, hypernatremia, etc), insulin levels, altered liver function and possible abnormal renal function.
I strongly suggest you reconsider your weight loss strategy to optimize both your immediate results as well as your long-term weight control plan. The best way is gradual weight loss