There are three sources of fuel your body uses for energy: carbohydrates, proteins and fats. Carbohydrates are broken down into glucose, or blood sugar, and are your body's primary fuel source. When carbohydrates aren't available, your body relies on fat for energy. Protein is the main building block for muscles and tissues. In a pinch, protein can also be converted to glucose and used for energy.
While it may be new to you, the keto diet has actually been around since the 1920’s, when the Mayo Clinic reported its effectiveness for helping epilepsy (that is still the case). Since then, there’s strong evidence that the keto diet helps with weight loss as well as type 2 diabetes, prediabetes, and metabolic syndrome, says Jeff Volek, Ph.D., RD, professor in the department of Human Sciences at The Ohio State University in Columbus, Ohio and co-author of The Art and Science of Low Carbohydrate Living.
A keto diet has shown to improve triglyceride levels and cholesterol levels most associated with arterial buildup. More specifically low-carb, high-fat diets show a dramatic increase in HDL and decrease in LDL particle concentration compared to low-fat diets.3A study in the long-term effects of a ketogenic diet shows a significant reduction in cholesterol levels, body weight, and blood glucose. Read more on keto and cholesterol >
The premise of the ketogenic diet for weight loss is that if you deprive the body of glucose—the main source of energy for all cells in the body, which is obtained by eating carbohydrate foods—an alternative fuel called ketones is produced from stored fat (thus, the term “keto”-genic). The brain demands the most glucose in a steady supply, about 120 grams daily, because it cannot store glucose. During fasting, or when very little carbohydrate is eaten, the body first pulls stored glucose from the liver and temporarily breaks down muscle to release glucose. If this continues for 3-4 days and stored glucose is fully depleted, blood levels of a hormone called insulin decrease, and the body begins to use fat as its primary fuel. The liver produces ketone bodies from fat, which can be used in the absence of glucose. 
As the popularity of the Keto Diet has exploded in recent years the true nature of Ketogenic weight loss has gotten blurred. So what is Keto? Very simply Keto refers to Ketosis, the state into which your body enters when it shifts to burning fat for energy instead of carbohydrates. As carbohydrates and sugar intake is restricted, your body begins to break down its fat stores to use as a source of energy. Therefore, the very basics of a Ketogenic Diet are:
I have ate bacon everyday since starting Keto and have lost 78 pounds in 11 weeks. Most Keto recipes consist of bacon that I see actually. I see so many list of foods to avoid and I certainly find some of them to have some odd foods on them. Packaged sausage is another I have had as a protein and have had no issue. To each their own I guess, some things obviously work differently for others.
In the 1990s, Atkins published an update from his 1972 book, Dr. Atkins New Diet Revolution, and other doctors began to publish books based on the same principles. This has been said to be the beginning of what the mass media call the "low carb craze" in the United States. During the late 1990s and early 2000s, low-carbohydrate diets became some of the most popular diets in the US. By some accounts, up to 18% of the population was using one type of low-carbohydrate diet or another at the peak of their popularity. Food manufacturers and restaurant chains like Krispy Kreme noted the trend, as it affected their businesses. Parts of the mainstream medical community have denounced low-carbohydrate diets as being dangerous to health, such as the AHA in 2001 and the American Kidney Fund in 2002 Low-carbohydrate advocates did some adjustments of their own, increasingly advocating controlling fat and eliminating trans fat.
First reported in 2003, the idea of using a form of the Atkins diet to treat epilepsy came about after parents and patients discovered that the induction phase of the Atkins diet controlled seizures. The ketogenic diet team at Johns Hopkins Hospital modified the Atkins diet by removing the aim of achieving weight loss, extending the induction phase indefinitely, and specifically encouraging fat consumption. Compared with the ketogenic diet, the modified Atkins diet (MAD) places no limit on calories or protein, and the lower overall ketogenic ratio (about 1:1) does not need to be consistently maintained by all meals of the day. The MAD does not begin with a fast or with a stay in hospital and requires less dietitian support than the ketogenic diet. Carbohydrates are initially limited to 10 g per day in children or 20 g per day in adults, and are increased to 20–30 g per day after a month or so, depending on the effect on seizure control or tolerance of the restrictions. Like the ketogenic diet, the MAD requires vitamin and mineral supplements and children are carefully and periodically monitored at outpatient clinics.
Dr. Jockers, thank you so much for this clear and detailed article! I began a keto-style diet around August 2019. By late November, I had fallen from 197 lbs. to under 175 lbs., dropped from 28% to 18% body fat, and anecdotally felt much better in all aspects of my health. All of this occurred exclusively due to diet, I believe– I had almost no exercise routine to speak of, and my desk-based job is pretty sedentary. My family practice doc was surprised and happy with the results as well when I met with him in January… until my blood work came back showing total cholesterol at 257, triglycerides at 236, LDL-C at 162, and HDL at 50.
“I follow and recommend a low-carb or keto lifestyle, with and without intermittent fasting, to all of my patients whether or not they have lifestyle-related chronic conditions. I do this because of the health benefits to anyone who follows them, but also because of the science behind them and the impressive clinical results I have seen in my patients. I have recommended the Diet Doctor website for the past 5-6 years as a first-stop to find completely trustworthy information, delicious recipes, great visuals and excellent videos.”
In general, you want to eat the minimum amount of protein to preserve lean body mass and not overtax your kidneys. If you eat too much protein, the excess converts to glucose through a process called gluconeogenesis. You don’t want that to occur in ketosis. Instead, eat anti-inflammatory protein—at the minimum amount to preserve or build lean body mass. My favorite sources are wild-caught fish, grass-fed and -finished beef and wild meats (elk, bison, etc.), pasture-raised poultry, nuts, and seeds. Make sure fish has more selenium (which helps protect the brain) than mercury, to mitigate heavy metal toxicity. Good sources that have a safe selenium/mercury ratio include: tuna, opah, wahoo, spearfish, swordfish.
Helps to control type 2 diabetes and other metabolic disorders: If you have diabetes, you may be turning to the ketogenic diet as a way to control your insulin and glucose levels. Early research shows that the ketogenic diet can help you significantly improve insulin sensitivity levels (11). One study even shows that some diabetes patients were able to stop taking their diabetes medication altogether while on the keto diet (12)!