Cyclical ketogenic diet: The Bulletproof Diet falls into this category. You eat high fat, low carb (less than 50 grams of net carbs a day) five to six days of the week. On day seven, you up your carb intake to roughly 150 grams, during what’s called a carb refeed day. Carb cycling this way helps you avoid the negative effects some people experience when they restrict carbs long term, like thyroid issues, fatigue and dry eyes.  Full ketosis isn’t for everyone, and adding carbs such as sweet potatoes, squash, and white rice one day a week keeps your body systems that need some amount of carbs functioning properly.
Normal body cells metabolize food nutrients and oxygen during cellular “respiration”, a set of metabolic pathways in which ATP (adenosine triphosphate), our main cellular energy source is created. Most of this energy production happens in the mitochondria, tiny cell parts which act as powerhouses or fueling stations. There are two primary types of food-based fuel that our cells can use to produce energy:
So you've decided you want to try out the high-fat, low-carb diet, better-known as the fat-burning ketogenic diet. Whether it's to lose weight, have more energy, or fuel workouts differently, going keto is a popular choice right now. But figuring out a keto meal plan on your own is no easy feat, especially since eating a diet super high in fats doesn't come naturally to many people who are accustomed to the traditionally carb-heavy American diet. (It's especially hard if you're vegan and want to try keto.) But this should help: Keto experts explain how to set yourself up for success, plus provide ideas for exactly what keto foods to eat when you're first getting started. (While you're at it, check out these Low-Carb Keto drinks That Will Keep You in Ketosis.)
Although the hunger-reducing effect of KD is well-documented, its main mechanisms of action are still elusive. The global picture is complicated by the contradictory role of ketosis on anorexigenic and orexigenic signals (summarized in Figure Figure4).4). Ketones (mainly BHB) can act both orexigenically or anorexigenically. In the orexigenic mechanism, it increases the circulating level of adiponectin, increasing brain GABA and AMPK phosphorylation and decreasing brain ROS production. The anorexigenic mechanism triggers a main normal glucose meal response, increasing circulating post-meal FFA (thus reducing cerebral NPY), maintaining CCK meal response and decreasing circulating ghrelin. It can be postulated that the net balance of the contrasting stimuli results in a general reduction of perceived hunger and food intake. More studies are needed to explore the mechanism of potential beneficial effects of KD on food control.
If you give your body any more than the absolute minimum amount of protein that it needs, it will immediately break it down into carbs. This is why keto sites often give a guideline for not eating too much protein. The problem is that there’s no one guideline that works for everyone, and without specifically tailoring keto to your body it’d be easy to accidentally ingest too much protein.
In terms of weight loss, you may be interested in trying the ketogenic diet because you’ve heard that it can make a big impact right away. And that’s true. “Ketogenic diets will cause you to lose weight within the first week,” says Mattinson. She explains that your body will first use up all of its glycogen stores (the storage form of carbohydrate). With depleted glycogen, you’ll drop water weight. While it can be motivating to see the number on the scale go down (often dramatically), do keep in mind that most of this is water loss initially.