Its moniker should be "the magic diet" or "the closest thing we have to proof that God exists diet." I will swear on my life itself that this diet works and I am not sponsored by any company, I promise.
The goal of the keto diet is to eat as few carbs as possible, or maintain a high fat, moderate protein, low carb ratio. In a (high fat low carb) nutshell, your body generally uses carbs as its main fuel. Your brain, heart, kidneys, muscle all break down carbs into glucose/fructose which are broken down further to be converted into high energy particles to run on. However if your body doesn't have enough carbs, it will have to use something else to use as fuel. If you hadn't figured it out, that is fat. By restricting carbs, you basically forces your body to start breaking down fat into molecules called ketones to use as energy instead, and so you are preferentially losing fat on this diet. This is obviously psychologically very appealing, but personally I've found that the main way keto works is that by eating mainly protein and fat, I am able to stay full for much longer than from eating carbs, and end up very easily maintaining a caloric deficit. I get to eat delicious meat, vegetables, and other fatty foods, know that I'm burning fat for a fact, and feel fuller for much longer, thereby losing weight. It's nothing short of scientific magic.
As with all things in life that sound suspiciously too good to be true, there are some cons to this diet. First, you must be VERY strict. Eating just a few too many carbs will kick you out of ketosis (the state of breaking down fats into ketones) since your body sees the carbs and is like Oh so we're back in business with the getting carbs thing? Well fuck you, fat, this is much easier to use! And that's it, you're not on keto anymore. Staying strict is by far the hardest part; no bread, pasta, potatoes, cereal, or SUGAR of any kind. That also means no desserts, fruits, or juices, as they are all high in sugar (which contain sucrose, which breaks down into fructose/glucose so you might as well be eating bread.) This is not something everyone knows: sugar is sugar. The carbs you get from a cookie end up breaking down into the same basic units as the carbs you get from an apple, despite the apple being seen as healthier considering its vitamin/fiber content. In keto eyes, they're both the same kind of evil. Another issue with the diet is that since you're eating so much protein, it is better to drink shittons more water. For someone who is on the diet longterm, eating tons of protein and dehydrated, all that protein will fuck up your kidney. But I don't think it's common. That's basically it. You have to be strict, no cheating, and drink lots of water.
People think Oh my god I could never go on this diet, what would I do without my toast every morning/pasta/potatoes/etc? How could I never eat cake/cookies/brownies/candy, not even a bite? For people who mainly subsist off carbs, yes this would be a very difficult change. But I have always preferred meat/savory foods to sweet foods. I do love certain carbs, but there is an immense variety to this diet. Your proteins can come from steak, chicken, fish, beans, eggs (which have their own endless ways to be used). I end up eating tons more vegetables than I would normally, I've made delicious broccoli, cauliflower, asparagus, Swiss chard, and spinach dishes. The best part is that this diet is meant to be high fat, meaning you can eat much more bacon, butter, sausage, and fatty nuts like walnuts, cashews, almonds, and macadamia nuts than allowed on a diet based solely on caloric restriction. And by using almond flour or coconut flour, there are tons of recipes to make bread, tortillas, and countless desserts if you are hoping to replace your normal carbtastic items.
Over the course of the first month and a half, I lost probably 10 pounds. Nothing I had ever tried had had any results before, and I had been converted into an unshakeable believer. Then I became lax, started cheating once a week or so and lost another 10 pounds over the summer, slowly. I was at my lightest (153) around early September of this year. Then school started picking up, and I got into a month long stretch of school/tests stress plus a mentality of "I'm going to restart keto soon so I should eat anything and everything delicious before then" and over the course of a month and a half, put on almost 10 pounds. It was pretty devastating. I for some reason hadn't thought it a possibility to put on that much weight after tasting the glory of actually feeling thin for those amazing weeks. So now I'm on keto again, and have dropped 6 pounds, mostly from water weight tied up with glycogen (how your body stores extra carbs.) I'm pumped up and motivated, hoping to hit at least 150 by Thanksgiving. I've done great this past week and plan to not cheat the next five. Coming up next: one of my favorite keto recipes, goat cheese meatloaf!