During the initial 2 weeks on keto, you will lose up to 10 lbs, but this is mostly water weight as keto has a strong diuretic effect . Water weight loss happens as your body starts to deplete its glycogen stores which results in water and electrolyte loss (because glycogen is four parts water).
If you stop eating keto during this trial period, soon enough you'll regain this water weight. But if you persist, your body will get into ketosis and start burning its fat stores and this lost fat will likely stay off as promised by current research.
According to a recent study involving 20 obese subjects who lost 44 lbs after 4 months on a low-calorie keto diet, their resting metabolic rate (RMR) and weight did not change even after increasing their calorie intake 3 months later . The reason why RMR is important for sustained weight loss is because weight loss usually leads to drops in RMR and this causes people to regain weight after some time.
A recent literature review also found that reduced calorie ketogenic diets were more effective for long-term weight loss than other diets . It's important to note here that the best results come from a calorie restricted ketogenic diet. You may have heard that calorie restriction isn't important on keto. And while this is true to some extent, it can also be misleading - the main reason calorie counting isn't essential on keto is because it's difficult to overeat on this diet and because this diet suppresses appetite .