The keto diet is most assuredly not a fad, at least not in the usual sense of the word. It’s been around for nearly a century, and has its roots in the medical world: In the 1920s, epilepsy researchers found that increased levels of ketones in their patients resulted in fewer seizures, and the diet is still a widely accepted treatment for epilepsy today. There’s also some evidence that a ketogenic diet has therapeutic potential for a wide array of symptoms and diseases, including cancer, polycystic ovary syndrome, neurological conditions, diabetes, and even acne.
While macros will differ a little from person to person, the general rule of thumb for keto is to keep carbohydrates under 5% of your daily caloric intake. As long as you avoid the foods mentioned above, you should be fine. Google “TDEE calculator” if you need some additional guidance on how many calories to eat. I’ve had success following this way of eating as it allows me to eat foods that taste great. There are tons of resources online as well if you need additional guidance. A quick google search should turn up a ton of resources. Hope this helps!