Slowing down your metabolism will eventually lead to weight gain. One of the advantages of an LCHF lifestyle is that your are not eating too few calories, just eating the right ones
https://authoritynutrition.com/6-mistakes-that-slow-metabolism/
Intermittent fasting on the other hand has many health advantages without the risk of slowing metabolism.The entire strategy of weight loss with intermittent fasting hinges on lowering insulin.
Insulin is the primary driver of obesity. Therefore, for most people, reducing insulin is the best method of treating obesity. Low Carb lifestyles are a powerful method of reducing insulin and can be aided greatly by intermittent fasting
https://authoritynutrition.com/intermittent-fasting-guide/
The expert on intermittent fasting is Dr Jason Fung, check him out on
https://intensivedietarymanagement.com/theory/