As you can read elsewhere on this blog, humans’ blood glucose system and fight-or-flight mechanism evolved in a world that bears little resemblance to modernity. There’s another Stone Age inheritance, called ketosis, you should know about because of how it can affect your metabolism.
Discussions of nutrition and energy usually center around three macronutrients—carbohydrates, fats, and proteins. For most people, these are the basis of almost all calories consumed, and subsequently converted into energy for daily activities and bodily maintenance. (The ethanol in alcohol is a separate source of calories, one that ideally doesn’t contribute significantly to your caloric intake.)
But your body has another energy system that developed to keep us alive when exogenous calories(dietary calories) from carbs, fat, and protein are scarce or unavailable. When your body is starved of carbohydrates—whether through a food shortage, or a dietary choice—your body creates an emergency fuel known as ketone bodies. This so-called “fourth macronutrient” is produced in your liver from your body’s fat stores. Ketones provide the means for the liver to produce ‘new glucose’ by the process of gluconeogenesis, it also supplies a sustained energy to your muscles and, crucially, your brain (the latter of which is usually fueled by the carbohydrate glucose).
The state your body enters into in fueling itself with ketones is called ketosis. For our ancient ancestors, ketosis wasn’t a desirable condition—it meant that death from starvation was perhaps only weeks away. Also, while ketosis provides adequate energy for most activities, being in a ketogenic state can limit your ability in high-intensity activities, such as fast running, which are most efficiently fueled by glucose. That wouldn’t have meshed well with, say, outrunning a hungry predator in fight-or-flight situations.
Ketosis as a choice
Today, however, some people purposefully enter ketosis. Why? One major reason is that being in ketosis keeps your blood glucose levels from fluctuating excessively. Ketosis provides a slow but steady source of energy, eliminating the boom-and-bust cycle so many people assume is normal. As we’ve described elsewhere, those glucose spikes and crashes can lead to increased fat storage and an increased risk of type 2 diabetes.
Ketosis can also help you reach weight-loss goals. Regularly having higher levels of circulating ketones can alter your metabolism so that you draw more energy from your fat stores.
There are three primary ways to enter a ketogenic state. First, as we’ve seen, is to be approaching starvation. We don’t recommend this approach.
Second, exogenous ketones—that is, those you consume—can quickly but temporarily boost your ketone levels. Ketone salts and ketone esters are available commercially. They’re sometimes marketed toward athletes, from the angle that, when consumed in combination with traditional sport drinks, they can enhance performance by sparing some of your body’s carbohydrate stores. Staying in a ketogenic state via such products is neither practical nor affordable for most people.
The third way is to follow a ketogenic diet. Following a low-carb, high protein/fat diet can significantly elevate ketone levels without the extreme of nearly starving yourself to death. We'll cover this issue extensively in coming posts.