What is Keto ?
- Keto is short for metabolic ketosis. It's a metabolic condition where instead of burning glucose (sugar) your body burns fat and makes ketones the brain needs to function.
- Keto IS NOT a list of foods you are allowed or not allowed to have. There are plenty of diet plans and religions like that. Think Paleo or Kosher, even Halal; but any food can be keto if eaten in a small enough portion.
Confused? Ok let me try to explain.
The human body can accept 4 kinds of fuel for energy. These are the basic macronutrients that make up food -- alcohol, carbohydrates, fat, and protein. Alcohol is not calorie free and that's a nutrient the body converts to energy and metabolizes in the liver. It's the first thing burned by the body for fuel when it's ingested. We all know what protein is. That's meat, nuts, and sometimes dairy.
Fat is easy to identify, thanks to the low fat craze of the 1980s and 1990s, we can label butter and oils as fat. So what are carbohydrates? Well it's everything else. Literally everything from sugar, fruit, grains, pasta, rice, vegetables (generally) are all carbohydrates with varying degrees of natural sugar. Some come with fiber and others none at all.
if you restrict the amount of sugar and carbohydrates you eat, your body will burn fat and make ketones out of fat.
Out on the Internet there are many people who get quite religious about whether a food is keto or not. My perspective is any food can be keto if eaten in a small enough quantity. Now, the size might be so small you'll decide it's not worth it.
Common wisdom is to stay in nutritional ketosis reliably, you need to eat less than 7 carbs a meal and under 20 a day. Everyone has a different tolerance and that's a hardcore recommendation. Some people can go up to 50g of carbs or more daily.
So that's about it and if you want to read more about the subject, there are some great books on the topic. Probably the most approachable is Why We Get Fat and What to do About It by Gary Taubes.
Keto is not a new way of eating, in fact many think it's actually our ancestral diet.
Low carb eating was popularized by William Banting in the 1800s in his self published pamphlet, the Letter on Corpulence. Limiting sugar and starchy foods was well known to keep weight down and to manage diabetes. If you read old diet books, or menus, you'll see the diet meals recommended were bun-less hamburger patties with a salad and cottage cheese.
Dr. Robert Atkins, an American cardiologist popularized the low carb diet in the 1970s through his book, Atkins Diet Revolution.
Since then, keto dieting has come in and out of popularity, recently seeing a popular resurgence. However, the diet has been a tool used by bodybuilders, doctors, and health enthusiasts seeking body recomposition.
I hope this helps clarify a bit about keto and I encourage you to click the links I provided and if you want to know more, please check out the Extras section for books on this topic. 
