The biggest issue with rapid weight loss is that it requires significant effort in terms of diet and exercise, which is often unsustainable in the long term, leading to failure in maintaining weight loss. In contrast, a slow and steady approach to weight loss is more manageable and typically yields better long-term results.
If you lose weight too quickly, your body may not be able to "burn" fat efficiently, leading to loss of water and muscle mass instead of fat.
Experts recommend a weight loss rate of about 0.5 kilograms per week, and not more than 1 kilogram per week. Since 0.5 kilograms of fat contains about 3500 calories, you need to burn or reduce your intake by 500 calories per day to achieve this goal.
In some cases, faster weight loss can be safe if done correctly. For example, some obese individuals can lose weight quickly through a very low-calorie diet under medical supervision. Additionally, certain weight loss plans may allow for rapid weight loss initially (e.g., 2-4 kilograms in the first two weeks) and then slow down to about 0.5 kilograms per week, which can also be reasonable.