I posit that humans are cyclical omnivores, supposed to have periods of veganism and hypercarnivory, i.e. fasts and feasts. Just follow a fasting calendar such as this one. This practice predates even Christianity, it seems like the way humans would naturally eat in nature. Hunts weren't always successful, so they would eat plants, and when they were they feasted on meat. A similar pattern was followed in ancient Greece and Rome, where meat was also eaten only during festivals and holidays.
More specifically, I recommend:I do not recommend the ketogenic diet, carnivory, veganism, fruitarianism or the Ray Peat diet.
Recommended reading: Vitamins and "Health" Foods: The Great American Hustle. It is trivially easy to get all the nutrients you need just from your diet. Supplements are at best useless, they aren't risk-free and can be expensive, especially proprietary blends. Just save your money. Also see Hypervitaminosis: A Global Concern