The ketogenic diet is built on the principle of ketosis. Ketosis simply refers to the metabolic process through which the body uses fat as its primary source of energy rather than carbohydrates.
In a typical carb-centered diet, the body uses carbohydrates as an immediate source of energy because they can only be stored in limited quantities. As soon as food enters your mouth, the body begins to break it down into its most basic components which, for carbohydrates, are largely glucose molecules. Glucose is easily absorbed through the walls of the small intestine and then travels to the liver, after which it enters the blood stream. As blood glucose levels rise, the body’s cells absorb the glucose and utilize it for energy.
Insulin, a hormone secreted by the pancreas, plays an important role in glucose metabolism. As blood sugar levels rise, insulin secretion increases to enable the cells to absorb and utilize glucose. Insulin also plays a role in glucose storage. When blood glucose levels remain elevated beyond the energy needs of your cells, insulin helps convert the extra glucose into larger molecules called glycogen.
Glycogen is stored in the liver and muscles and can be used as a back-up source of energy for times when glucose is not readily available. Once those glycogen stores are gone, the body resorts to another energy source – stored fat. When the body begins to rely on fat rather than carbohydrates for fuel, it enters the metabolic state of ketosis.
What are Ketones?
When carbohydrate consumption is drastically reduced, it forces the body to burn stored fat as an alternative source of fuel. The process through which the body burns fat for energy results in byproducts called ketones. Also known as ketone bodies, ketones come in three different types:
Beta-hydroxybutyric acid (BHB)
In a state of ketosis, the first ketone to form is acetoacetate. Acetoacetate is then converted into beta-hydroxybutyric acid (BHB) and then into acetone. Technically speaking, beta-hydroxybutyric acid is not actually a ketone due to its unique chemical structure, but it can be grouped with acetoacetate and acetone in the context of the ketogenic diet.
Acetone is the simplest ketone but also the least-used – if the body doesn’t need it for energy it is broken down and excreted as a waste product, primarily through breath or urine. This particular ketone is responsible for the fruity smell on the breath when someone goes into ketoacidosis, a life-threatening condition and serious complication of poorly managed diabetes.
If glucose levels in the blood remain consistently low, the body will adjust to burning stored fats instead. Over time, ketone levels in the blood will rise and once they reach a certain point, the body enters the metabolic state of ketosis. The length of time it takes to enter a state of ketosis depends on numerous factors including carb intake, genetics, medical history, body composition, and energy needs.
Ketones as a Source of Energy
It is a common misconception that glucose is the most efficient source of energy for the body. While it may be the most readily available, particularly among people in the Western world, it is not necessarily the best energy source. In fact, the bran runs better on ketones than glucose.
The body is only capable of storing glucose from carbohydrates for a day or two. This can be problematic because the brain requires a great deal of energy to maintain proper function – if glucose stores are depleted, the brain would shut down after a few days with no food. The alternative would be breaking down muscle proteins into glucose, but that is a highly inefficient process.
Fortunately, the brain works very well using ketones for energy rather than glucose. Ketosis exists to ensure that the brain always has a steady supply of energy, even in the absence of food. The brain does require some carbohydrate to run efficiently, but it does perfectly well in a state of ketosis.
Not only are ketones an efficient source of energy for the brain, but they can also be beneficial for athletes. It is often assumed that carbohydrates are the best source of fuel for endurance athletes and bodybuilders because they can be accessed easily and burned quickly. Research suggests, however, that the body can become keto-adapted – it can become efficient in burning stored fat and ketones for energy to fuel even the most extended and strenuous workouts.
In a 2016 study published in the journal Metabolism, endurance athletes were asked to follow a ketogenic diet for 20 months. The results of the study showed that these athletes burned 2.3 times more fat than athletes following a high-carb diet during a three-hour run. The study also revealed that the rate of glycogen use and repletion both during and after the run was remarkably similar between the low-carb and the high-carb athletes. This is a perfect example of the body becoming keto-adapted and learning to burn fat for fuel just as (or more) efficiently as glucose.
Another study published in the Journal of Applied Physiology supports the theory that fat provides a better source of energy than carbohydrates for low- to moderate-intensity exercise. A third study showed that athletes following a ketogenic diet burned fat at up to 70% of their maximum intensity during exercise while athletes following a high-carb diet burned fat at just 55%.
Given the results of these and other studies, several conclusions can be drawn regarding the benefits of ketosis for athletes and for exercise in general:
Ketones may reduce fatigue during extended periods of exercise
The body can become keto-adapted to burn fuel during low-to-moderate exercise
A ketogenic diet improves fat burning during exercise
Keto-adaptation can reduce reliance on carbs (food) during extended exercise
A diet that promotes fat loss is beneficial for improving fat-to-muscle ratio
Though ketosis can be very beneficial for endurance athletes, there is some concern that the ketogenic diet may contribute to the depletion of muscle glycogen during extended periods of exercise. More research is needed, but some studies have suggested that low-carb diets may preserve muscle glycogen in some athletes. In one study, the ketogenic diet was found to prevent endurance athletes from “hitting the wall” during extended exercise – this is simply an expression used to describe the sudden onset of fatigue resulting from the depletion of glycogen stores in the liver and muscles.
The Benefits of Ketosis
While it may take time for the body to enter a state of stable ketosis, once it does you are likely to experience a number of benefits. Generally speaking, once the body becomes keto-adapted, you will notice improved energy levels and mental focus, improved blood sugar control, suppressed hunger and reduced cravings, as well as weight loss (primarily from fat). It has also been shown to benefit serious and chronic conditions like heart disease, diabetes, metabolic syndrome, Alzheimer’s and cancer.
Improved Energy and Mental Focus
In a state of ketosis, the body is able to burn fats for energy – this process is much more efficient than the process of metabolizing carbohydrates. A more efficient source of energy enables the body to run at its optimal level which improves energy levels as well as mental focus. Though there may be a brief adjustment period during which you experience fatigue and mental fog, once the body becomes keto-adapted those symptoms disappear and everything begins to work better.
When it comes to improved energy, it all comes down to keto-adaptation. When ketones become the primary source of energy for the body, the muscles adapt to converting acetoacetate into beta-hydroxybutyric acid, a highly efficient source of fuel for the brain. Anything that cannot be utilized is excreted from the body as waste.
Another metabolic process that contributes to improved energy and mental focus on the ketogenic diet is called glucogenesis. Glucogenesis is the process through which the body synthesizes or produces glucose from non-carbohydrates sources. This process primarily takes place in the liver where glucose is produced from glycerol and protein as well as other substances like lactate and pyruvate. Glucogenesis is an essential piece of the ketogenic puzzle because it ensures that organs like the brain which still require a small amount of glucose get what they need in the absence of dietary carbohydrates.
Improved Blood Sugar Control
A carb-centered diet is typically rife with blood sugar spikes and crashes. When you consume high-carb foods, the body breaks the food down very quickly which causes a sudden increase in blood sugar. Elevated blood sugar triggers the production of insulin in the pancreas to enable cells to absorb and utilize glucose from the blood stream. As blood sugar drops, insulin production decreases and everything normalizes.
The problem with the typical Western diet is that it is so focused around high-carb foods, that blood sugar often remains elevated for longer than is normal – this can cause the body to develop a diminished response to insulin or to produce less of it. This is known as insulin resistance and it is a key factor in the development of type 2 diabetes.
By largely removing carbohydrates from the equation, ketosis prevents the dangerous cycle of blood sugar spikes and crashes. Take for example the results of a 24-week study published in the journal Nutrition & Metabolism in 2008. In this study, 84 volunteers with both type 2 diabetes and obesity were randomly split into two groups based on diet – a low-carb ketogenic diet (LCKD) and a low-glycemic, calorie-reduced diet. At the end of the study it was revealed that both groups experienced a reduction in fasting glucose and insulin levels, but the low-carb ketogenic group showed greater improvements. In fact, in 95% of participants in the LCKD group were able to reduce or eliminate diabetes medications.
Weight Loss (and Fat Loss)
In addition to offering benefits for athletes, the ketogenic diet is beneficial for weight loss in general. Ketosis supports weight loss in the following ways:
It increases fat oxidation, burning both dietary fat and stored fat as its main source of fuel.
It regulates hormones that affect weight, reducing cravings for unhealthy foods.
It suppresses appetite, helping you feel full even while operating at a calorie deficit.
It prevents the blood sugar spikes that can cause hunger too soon after eating.
It reduces consumption of “empty calories” from carbs and processed foods
Another benefit of the ketogenic diet for weight loss is that it is easier to stick to than many diets. Low-fat and calorie-restricted diets often lead to hunger which increases the temptation to go off the diet. By burning stored fats for fuel, the body has a constant source of energy available so, not only will you burn fat and lose weight, but you will not be plagued by constant hunger and carb cravings.
To delve a little deeper into this particular benefit, consider the results of a 2015 study published in Frontiers in Psychology that tested the relationship between a ketogenic diet and food intake control. Though it is not quite clear how ketosis suppresses appetite, the results of this study suggest that ketosis alters the levels of hunger hormones in the blood – namely, ghrelin and cholecystokinin – which helps regulate appetite and lower food intake. This is partially why the ketogenic diet is so beneficial for intermittent fasting, something that will be discussed at length later in this guide.
Protection from Chronic Disease
While it is not entirely clear how the ketogenic diet helps to prevent or manage chronic conditions, researchers believe that it has something to do with certain biochemical changes in the body resulting from ketosis that improve brain signaling and function.
A key example of the medical benefits of ketosis is the use of the ketogenic diet in treating epilepsy, particularly in children who have not responded to anti-seizure medications. In clinical trials, nearly 40% of children following a ketogenic diet experienced greater than a 50% reduction in seizures compared to 6% in the control group. Furthermore, 7% of children in the diet group had greater than a 90% reduction in seizure activity.
The ketogenic diet has been tested and shown beneficial for a number of other neurological conditions including stroke, Parkinson’s disease, Alzheimer’s disease, and more. Studies suggest that the ketogenic diet works for these conditions by improving energy utilization in the brain for reduced disruptions in neural and nerve activity within the brain.
They also suggest that ketosis helps to trigger biochemical changes that prevent the short circuits within the brain’s signaling system that contribute to cellular damage and tumor growth.