What's known.

Ketogenic diets are accomplished by reducing starches and sugars in the diet to very low levels. Most people in the U.S. still consume 300-400 grams (1200-1600 Calories) of carbohydrates (i.e. mostly starches and sugars) per day. By way of contrast, a ketogenic diet is usually less than 50 grams/day (i.e. less than 200 Cal).

There has been much controversy over the years about the safety of ketogenic diets: for weight loss, diabetes, lipid disorders, epilepsy and other neurologic disorders and now cancers. Most of this controversy has centered around the 'fact' (sic) that since ketogenic diets are high in fat (true), they must therefore be bad for our cholesterol levels and therefore our heart (false).

Let's put that to rest immediately: There are only three macronutrients: Carbohydrates (CHO), protein and fat. Since 1982 the USDA has recommended a low fat diet (<30% fat). Since there's only so much protein you can eat, the reality, and the recommendation of the USDA was to consume 55-70% of Calories as CHO. This has been a public health disaster marked by alarming and epidemic levels of public obesity, lipid disorders, and type 2 diabetes. And the reason has been clear biologically from the beginning: 1. CHO increases insulin levels in the blood; 2. Insulin drives both fatty acids and sugar into fat cells; and 3. insulin inhibits the breakdown of fat in fat cells. IN SHORT: High insulin, driven by excess dietary CHO, MAKES US FAT AND KEEPS US FAT. Further, excess fat (especially visceral fat, i.e. under our abdominal muscles), once deposited, becomes toxic and sends off toxic molecules to the rest of the body. Finally, these toxic molecules then predispose us to type 2 diabetes and cancers. 

Furthermore, total cholesterol as a marker of cardiovascular risk is at least 30 years out of date. Much better markers are HDL (high density lipoproteins) and triglycerides (TG). HDL, the 'good' cholesterol, goes UP on low carbohydrate diets, and DOWN on high carb low fat diets. TG goes DOWN on ketogenic diets and UP on high carb diets. So the risk markers for cardiac disease are actually reduced on ketogenic diets.

In summary: The idea that fat makes us fat is very intuitive and easy to grasp. BUT IT's COMPLETELY WRONG. The body handles our macronutrients differently: starches and the sugars make us fat, keep us fat, and predispose us to bad diseases like obesity, diabetes, heart disease and cancers.