For 'weight' (or rather, body fat) to be lost permanently, it must be reduced slowly . A loss of no more than 2 pounds a week should be considered realistic, without affecting health. This can be achieved through a combination of healthy eating but, most importantly, increased activity - preferably with an effective exercise programme that develops your body's ability to 'burn up' fat.
The concept of 'weight' loss must be clearly understood. Bathroom scales give a misleading measurement of 'weight'. They cannot take into account hydration levels. Water has weight - lose it or retain it and 'weight' is affected.
This is the illusion created by 'fad' diets, which cause considerable water loss during the first few days.
Women, particularly, notice fluctuations in weight as a result of water retention during their monthly cycle.
To be sure that weight lost is actually fat loss, body composition needs to be measured and analysed throughout a weight (fat)-loss programme. This can be done quickly (and painlessly!) by a process called bioelectrical impedance analysis.
It can then be remeasured, perhaps monthly, to monitor changes in body fat levels.