When it comes to weight loss, keto diets focus on burning fat rather than carbs. Typically, carbohydrates are the body's primary fuel source. On a keto diet, fat becomes the primary fuel source.
But, going keto isn't for everyone. Cutting carbs to 20 grams a day is hard for many people; our brains alone need 120 grams of carbs to function, and the U.S. Dietary Guidelines for Americans recommends 130 grams of carbs daily. (To give you an idea of what 20 grams of carbs is, one small banana has 23 grams.)
Reducing your carb intake so drastically means foods like pasta, bread, rice, and even some fruits and vegetables like beans, peas, corn, potatoes and onions, are out. Some of these are also rich in fiber, so eliminating them from your diet could cause constipation. Because the brain prefers carbs for energy, a ketogenic diet could make you irritable and moody, cause headaches, or make you feel like you have brain fog.
One of the other dangers is having too many ketone bodies in your blood, which can happen after being on a ketogenic diet too long, or if your body doesn't produce enough insulin to restrict the ketones. The excess causes ketoacidosis, which is toxic.
And, of course, another danger is the diet can be high in saturated fat. "The diet focuses largely on fatty foods, and the increased amount of saturated fat can be harmful," Smith says. "Diets high in saturated fat are linked to heart disease."