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Dear Mark,

What are ketones? How does ketosis play into the Primal Blueprint? Did our bodies evolve to run on ketones? If not, why do they exist?

Ketones, to put it briefly, are compounds created by the body when it burns fat stores for energy. When you consume a diet very low in carbohydrates, the body responds to the significantly lowered levels of blood sugar by flipping the switch to another power source. The body converts fatty acids in the liver to ketones. Ketones, then, become the main energy source as long as blood sugar levels remain low.

Recently, researchers have discovered more about the unique mechanisms behind this energy "switch." It turns out a specific liver hormone, FGF21, is essential for the oxidation of the liver's fatty acids. Furthermore, animals who were fed a ketogenic diet over time showed "increased expression of genes in fatty acid oxidation pathways and reduction in lipid synthesis pathways." In other words, their bodies adapted metabolically and genetically to the diet.

Ketosis was crucial to our evolution. Given the relatively minor role of carbohydrate-rich foods (even the consumption of many tubers is thought to have come later with the advent of cooking practices), our bodies were fairly frequently operating in the arena of ketosis. Add to this the fasts and famines of primal living, and it's clear that ketones served as an essential energy source.

The Primal Blueprint recommends "generally" about 100-150 grams of carbohydrates a day, but many who follow it or the related paleo principles choose diets that fall in the realm of 50-80 grams a day, a practice (along with IF) that spurs the body to turn on ketosis as needed. These practices encourage "upregulation" of the body's fat-burning metabolic functioning and "down regulation" of fat storing systems. For those looking to lose fat, this becomes an extremely effective tool. On the other hand, after spending a few days or weeks in a predominantly ketosis mode, it may behoove you to do an occasional higher carb day (maybe 250-300 grams) to simply readjust insulin sensitivity. This is particularly appropriate if you have achieved an ideal body composition (lean body mass and body fat) and don't need to lose more fat. An essential part of the Primal Blueprint includes both the fat-burning upregulation and the periodic honing of the body's systems and adaptive responses.

Finally, ketogenic diets, which are generally lumped together by critics, have gotten a lot of bad press. While experts have generally recognized their effectiveness for weight loss, very low carb diets that result in ketosis (like the Atkins) have been criticized on health grounds. The problem with these criticisms? They're based on diets that allow for 20 grams or less of carbohydrates a day. While I believe we are not meant to run primarily on carbohydrate energy, I do believe we depend on the nutrients offered by low carb vegetables and even some low glycemic fruits. A diet of 20 carbohydrate grams simply can't allow for the plentiful intake of nutrient-rich vegetables.

When your carb intake is low enough, say 50-80 grams a day, ketosis kicks in when it needs to. Over time, this process becomes efficient as the body "unfolds" in its genetic expression. Yet this carb intake is high enough that you can freely include copious amounts of nutrient- (including potassium) rich vegetables to offer the body sufficient nutrition, fiber, and alkalizing minerals. At 100-150 grams a day, again all from just veggies and fruits, you probably won't hit ketosis, but you also won't prompt a rise in insulin or fat storage.

Thanks, as always, for your questions. Look for more on low carb living this week. In the meantime, keep the questions and suggestions coming!

Further Reading

The Definitive Guide to Grains

What Happens to Your Body When... You CARB BINGE?

Act "As If" - A 30-Day Primal Health Challenge