Over 8–10 mmol/l: It’s normally impossible to get to this level just by eating a keto diet. It means that something is wrong. The most common cause by far is type 1 diabetes, with severe lack of insulin. Symptoms include feeling very sick with nausea, vomiting, abdominal pain and confusion. The possible end result, ketoacidosis, may be fatal and requires immediate medical care. Learn more
On the ketogenic diet, carbohydrates are restricted and so cannot provide for all the metabolic needs of the body. Instead, fatty acids are used as the major source of fuel. These are used through fatty-acid oxidation in the cell's mitochondria (the energy-producing parts of the cell). Humans can convert some amino acids into glucose by a process called gluconeogenesis, but cannot do this by using fatty acids. Since amino acids are needed to make proteins, which are essential for growth and repair of body tissues, these cannot be used only to produce glucose. This could pose a problem for the brain, since it is normally fuelled solely by glucose, and most fatty acids do not cross the blood–brain barrier. However, the liver can use long-chain fatty acids to synthesise the three ketone bodies β-hydroxybutyrate, acetoacetate and acetone. These ketone bodies enter the brain and partially substitute for blood glucose as a source of energy.
The primary outcome, hemoglobin A1c, decreased from 7.5 ± 1.4% at baseline to 6.3 ± 1.0% at week 16 (p < 0.001), a 1.2% absolute decrease and a 16% relative decrease (Table (Table4).4). All but two participants (n = 19 or 90%) had a decrease in hemoglobin A1c (Figure (Figure1).1). The absolute decrease in hemoglobin A1c was at least 1.0% in 11 (52%) participants. The relative decrease in hemoglobin A1c from baseline was greater than 10% in 14 (67%) participants, and greater than 20% in 6 (29%) participants. In regression analyses, the change in hemoglobin A1c was not predicted by the change in body weight, waist circumference, or percent body fat at 16 weeks (all p > 0.05).
For people with Type 1 Diabetes, you probably have heard of their diabetic emergency, diabetic ketoacidosis, also referred to as DKA. This can be life threatening condition for people with Type 1 diabetes and Certified Diabetes Educators spend many hours teaching preventive care for DKA. This condition should not be confused with nutritional ketosis, the fat burning state reached when following the Ketogenic diet. The two conditions are quite different.
By restricting carbs to the degree that the keto diet recommends, you will stimulate the production of ketones and eventually enter nutritional ketosis. As a result, you will start burning more ketones for fuel. Ketones have also been found to help increase weight loss, lower glucose and insulin levels, decrease insulin resistance, and improve energy efficiency.  
Thanks to its flexibility, easy-to-understand system, and group support, Weight Watchers came out way (weigh?) ahead, winning "best weight loss," "best fast weight loss," and "best commercial diet" in the U.S. News & World Report rankings. (Oprah's endorsement probably didn't hurt either!) They recently revamped their signature plan to include "free" foods like chicken breasts and fresh produce so you'll never feel hungry even while dropping pounds. In addition, their app makes tracking your food a piece of cake—which you're totally allowed to have on the program, by the way. (Even better news: Research supports the fact that Weight Watchers is one of the best weight-loss diets.)
In the study, the researchers fed mice a ketogenic diet for several days and expected to find a favorable outcome — perhaps weight loss or another indication of improved health. Instead, they found that the liver began resisting insulin almost immediately and the mice were unable to regulate their blood sugar levels after only three days on the diet. (Insulin resistance, meaning that cells in the body don't respond to insulin, is a key characteristic of type 2 diabetes.)
The benefits above are the most common ones. But there are others that are potentially even more surprising and – at least for some people – life changing. Did you know that a keto diet can help treat high blood pressure, may result in less acne, may help control migraine, might help with certain mental health issues and could have a few other potential benefits?