Carbohydrates are traditionally known as the main source of energy for the body and organs. But there have been some newer trends like Whole 30, Atkins, and Ketogenic diets that significantly reduce the amount of carbohydrate that a person is allowed to ingest, replacing that carbohydrate with fat. In many cases these diets have led to weight reduction and improved blood glucose. Even still they are not diets approved or recommended by Doctors or Dietitians alike.
While fats are a welcome source of energy for most of the body, a few types of cells, such as brain cells, have special needs. These cells could easily run on glucose from the diet, but they can't run on fatty acids directly. So under low-carbohydrate conditions, like an extremely low carb diet or after prolonged fasting or exercise, brain cells require the body to make fat-like molecules called ketone bodies. This is why a very-low-carbohydrate diet is sometimes called "ketogenic." Ketone bodies are also related to a dangerous diabetic complication called ketoacidosis, which can occur if insulin levels are far too low. You could enter ketosis with as few as 20 grams or as much as 100 grams. The only way to really tell whether you’re in ketosis is to check via various testing methods (which each has its own problems with accuracy), urine test strips are the most common. Ketone bodies could alone provide enough energy for the parts of the body that can't metabolize fatty acids, but some tissues still require at least some glucose.
Instead, glucose can be made in the liver and kidneys using protein from elsewhere in the body. If not enough protein is provided by the diet, the body starts breaking down muscle cells.
Clinically approved recommendations for daily carbohydrate intake is around 45-65% of calories from carbohydrate. On a 2000 calorie diet, that means between 225 and 325 grams of carbohydrate per day. Low carbohydrate diets typically tend to be limited to around 50-70grams carbohydrate per day.
These are usually 25-30g or less of carbohydrates per day, or around 5-6% of a 2000 calorie diet. In place of carbohydrates, the diet in turn becomes around 60-75% fat and 20-35% protein.
There's a lot of research on ketogenic diets since it is extremely limiting and a big shock to the body given the drastic change that the diet must undergo. If you want to read our summary of the clinical research, here are some details.
Ketogenic diets may not be harmful in some cases, but in those cases where it may be safe more research is still needed to see how effective it is in treatment of disease. With many common illnesses a ketogenic diet is not safe and should not be considered. It may help with glucose management and weight loss in some patients, but the patient should ask the doctor to review their blood results to make sure it is safe to start. After beginning a ketogenic diet, the patient should be followed more closely with blood drawn more frequently throughout the process to make sure no adverse effects are shown.
For now, starting a ketogenic diet is still a very risky endeavor. More research is needed on the amount of fat, protein and carbohydrate that is safe, as well as the safest duration of a keto-diet and how to transition out of one.