The diet, “keto” for short, has taken the nutrition sphere by storm. While popular and evidence-based, many might not know exactly what ketosis is, how it works, and why it’s such a big deal. That’s what we’re here for.
What is Ketosis?
When we think about using energy, we often think about the process of “burning” carbohydrates and fats to provide the necessary fuel for cells to do work. Glucose is one of the main sources of energy for humans and animals—it’s usually obtained through dietary intake of carbohydrates: breads, fruits and vegetables, legumes, and some other less-healthy sources of refined carbohydrates and starches.
Some of the carbohydrates we consume are used to maintain blood glucose levels and fuel organs that can’t use substrates like fat for fuel, including red blood cells, some cells in the eye, and the brain. Any glucose not used is stored in the liver and muscle in glucose “chains” known as glycogen or will be converted into adipose tissue (body fat).
In certain situations, like during exercise or during the fasting state (~2+ hours after consuming a meal), we can “liberate” glycogen from storage sites and turn it into glucose if no external sources of glucose are coming in through diet. This is one way which we maintain blood sugar levels.
For instance, during prolonged exercise or fasting, muscle glycogen is broken down to provide energy.
Depending on fuel availability and the energy demands of the body, we are able to switch fuel sources from glucose to fat, and vice versa. This is termed “metabolic flexibility.”
No glycogen, no problem. The body can break down and release fatty acids into the bloodstream.
Fat is an energy-rich substrate, is a great source of fuel for the body, and most people have enough fat stores to last the body a long time. But, it turns out, some organs, like the brain and red blood cells, can’t use fatty acids as a fuel substrate—they lack the necessary enzymes to do so. Thus, they rely solely on glucose, either obtained through food or created through gluconeogenesis.
What happens then, if no glucose is available?
First, glycogen will be liberated from the liver and used for energy production. After about 24 hours, however, glycogen will begin to deplete unless carbohydrates are consumed from an external source.1 Now we need some sort of energy for organs which will otherwise become “starved” of energy.
Luckily, evolution has found a workaround to this problem—ketosis.
In response to glycogen depletion and low blood glucose, a slew of hormonal signals are initiated inside the body: insulin falls, glucagon rises, and cortisol increases, among others. These shifts are a signal for the body to burn fat; and stored fat is released from adipose tissue into the blood as free fatty acids (FFAs).
Once in the blood, FFAs trigger the production of ketone bodies, which occurs inside the liver. The process, termed “ketogenesis,” results in elevated levels of ketone bodies in the liver, including beta-hydroxybutyrate (BHB), acetoacetate (AcAc), and acetone.
Unlike fats, ketones can cross the blood-brain barrier and serve as a fuel source for our brain, with some research suggesting that up to 60% of the brain’s energy during starvation can come from ketone metabolism. This important adaptation was survival insurance.
Long ago, when cavepeople went long periods without an external source of energy, ketosis ensured they could not only survive periods of starvation, but allow for high-level body and brain function. Food needed to be hunted or gathered, and ketones provided the energy to do so.
What Role Does Ketosis Play Today?
For most of us, food availability today is nothing like that of prehistoric humans.
We can easily access high-energy, high-carbohydrate food sources. Our metabolic state is constantly on “fed.” On one hand, this is great—who doesn’t love a taco at 2am? But, our food-plenty lives come with a cost. Heart disease, type 2 diabetes, and other diseases of modernity have been attributed to increased consumption.
Many people are rarely exposed to a period of more than a few hours without food (other than sleep). We aren’t food-deprived, and therefore our bodies are never forced into a ketogenic state. This might be seen as a blessing of modern day.
But, are we missing out on some of the benefits ketosis can provide bodies? A little “stress” is sometimes a good thing.
Most research says yes, and this has paved the way for a rising interest in ketogenic diets—which are basically a form of a low-carbohydrate high-fat diet. The big difference between a “normal” diet and a very low carb diet (~20-50g carbs/day) is that on a ketogenic (keto) diet, the severe carbohydrate restriction results in the production of ketones by the liver.
As we will see, ketones act in a myriad of ways to exert several health benefits.
Ketosis vs. Ketoacidosis
Let’s clear the air here. People sometimes (incorrectly) confuse the terms ketosis and ketoacidosis. These are entirely different physiological states, and should be differentiated before we move on.
Diabetic ketoacidosis (DKA) is a condition often occurring in type 1 diabetes. It’s characterized by both high levels of blood glucose and high blood ketones—something that shouldn’t normally occur in human physiology.5
Since people with type 1 diabetes don’t produce insulin, levels in the body stay low, and the signal for muscles to take up blood glucose is absent, meaning glucose levels in the blood stay high as they are not being brought into cells to be used for energy. Low insulin levels, however, also signal for fatty acids to be released into the bloodstream. The result is increased liver ketone production, leading to abnormally high blood ketones and blood that becomes acidic (hence “acidosis”). Ketoacidosis is very harmful.
Ketosis, while also characterized by elevated blood ketones, occurs in the presence of LOW blood glucose. It’s a response to carbohydrate depletion; it’s completely physiological and an evolutionary advantage.
Beware of any articles that cite “ketoacidosis” as a negative aspect of ketosis or the ketogenic diet, unless in the context of diabetes.
