The ketogenic diet isnt new. But over the past few years, it has emerged as one of the most popular and polarizing ways to lose weight .

The eating plan has many people slashing their carb intake and loading up on healthy fats in an effort to reach the holy grail of the keto diet: ketosis, or the metabolic state in which the body starts burning its own fat for fuel.

Here are the basics of how things go down when youre on keto: Your bodys cells typically get their energy from carbohydrates. But when youre on keto, what youre really doing is starving your body of carbohydrates so it needs to go to the next energy source, which is fat, explained Rabia De Latour , a gastroenterologist and assistant professor of medicine at New York Universitys Langone Health. Your body then burns that fat.

The diet doesnt restrict you in terms of calories or the amount of food you eat. Instead, its all about what you eat . Most keto plans include lots of seafood, red meat, poultry, cheese, low-carb vegetables (sorry carrot and corn fans), eggs, plain yogurt and fats (hello, avocado). Youre instructed to avoid foods with sugar and carbs, like many fruits, grains and legumes.

Because of this, people who try keto can experience a range of side effects and symptoms as their bodies adapt to the low-carb, high-fat style of eating. Here are some of them:

You feel like you have the flu