What is a Keto Diet?
A keto or ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet that helps the body produce ketones (ketone bodies) and use them as fuel instead of carbohydrates.
The ketogenic diet was created to treat difficult-to-control (refractory) epilepsy in children, however, it is nowadays often used for the treatment of obesity as well. The original therapeutic diet for pediatric epilepsy provides just enough protein for body growth and repair, and sufficient calories to maintain the correct weight for age and height.
The ketogenic diet forces the body to burn fats rather than carbohydrates. Normally, the carbohydrates contained in food are converted into glucose, which is then transported around the body and is particularly important in fueling brain function.
However, if there is very little carbohydrate in the diet, the liver converts fat into fatty acids and ketone bodies – this is how weight loss occurs. The ketone bodies pass into the brain and replace glucose as an energy source.
The classic ketogenic diet contains a 4:1 ratio by weight of fat to combined protein and carbohydrate. This is achieved by excluding high-carbohydrate foods such as starchy fruits and vegetables, bread, pasta, grains and sugar, while increasing the consumption of foods high in fat such as cream and butter.
The simplified ketogenic diet is more forgiving of the fat to protein and carbohydrate ratio; instead, it imposes a rather strict maximum amount of carbohydrates per day, not exceeding 50g but oftentimes significantly lower than that.
In its most restrictive version, or during the initial week until the body enters the state of nutritional ketosis, the carbohydrate consumption is reduced to max. 20g per day.
For our purpose, a low-carbohydrate diet is ketogenic if it restricts carbohydrate consumption enough to cause ketosis.
In this regard, the induction phase of the Atkins diet is ketogenic. Low-carbohydrate diets (and therefore ketogenic diets) are used to treat or prevent some chronic diseases and conditions including: cardiovascular disease, metabolic syndrome, high blood pressure and diabetes, obesity, epilepsy, chronic fatigue syndrome and polycystic ovarian syndrome.
Ketosis and Weight Loss
A ketogenic diet forces the body to burn fats rather than carbohydrates. The mechanisms behind this behavior are explained below.
In western diets (and many others), most meals are sufficiently high in nutritive carbohydrates to evoke insulin secretion. The primary control for this insulin secretion is glucose in the blood stream, typically from digested carbohydrate. Insulin also controls ketosis; in the non-ketotic state, the human body stores dietary fat in fat cells (i.e., adipose tissue) and preferentially uses glucose as cellular fuel.
Diets low in nutritive carbohydrates introduce less glucose into the blood stream and thus evoke less insulin secretion, which leads to longer and more frequent episodes of ketosis.
Low-carbohydrate diet advocates in general recommend reducing nutritive carbohydrates (commonly referred to as “net carbs,” i.e., grams of total carbohydrates reduced by the non-nutritive carbohydrates) to very low levels.
This means sharply reducing consumption of desserts, breads, pastas, potatoes, rice, and other sweet or starchy foods. Some recommend levels less than 20 grams of “net carbs” per day, at least in the early stages of dieting (for comparison, a single slice of white bread typically contains 15 grams of carbohydrate, almost entirely starch).
By contrast, the U.S. Institute of Medicine recommends a minimum intake of 130 grams of carbohydrate per day (the FAO and WHO similarly recommend that the majority of dietary energy come from carbohydrates).
If the diet is changed from one that is high in carbohydrates to one that does not provide sufficient carbohydrate to replenish glycogen stores, the body goes through a set of stages to enter ketosis.
During the initial stages of this process, blood glucose levels are maintained through gluconeogenesis, and the adult brain does not burn ketones. However, the brain makes immediate use of ketones for lipid synthesis in the brain.
After about 48 hours of this process, the brain starts burning ketones in order to more directly use the energy from the fat stores that are being depended upon, and to reserve the glucose only for its absolute needs, thus avoiding the depletion of the body’s protein store in the muscles.
Is ketosis dangerous?
No, it is not. Ketoacidosis, not ketosis, is the dangerous condition you may have heard or been told about – many confuse the two, even practitioners!
In normal individuals, there is a constant production of ketone bodies by the liver. The concentration of ketone bodies in blood is maintained around 1 mg/dl. Their excretion in urine is very low and undetectable by routine urine tests.
When the rate of synthesis of ketone bodies exceeds the rate of utilization, their concentration in blood increases; this is known as ketonemia. This is followed by ketonuria – excretion of ketone bodies in urine. The overall picture of ketonemia and ketonuria is commonly referred as ketosis. Smell of acetone in breath is a common feature in ketosis.
When a type 1 diabetic suffers a biological stress event (sepsis, heart attack, infection) or fails to administer enough insulin they may suffer the pathological condition ketoacidosis.
Liver cells increase metabolism of fatty acids into ketones and glucose via glycogenolysis in an attempt to supply energy to peripheral cells which are unable to transport glucose in the absence of insulin.
The resulting very high levels of blood glucose and ketone bodies lower the pH of the blood and trigger the kidneys to attempt to excrete the glucose and ketones. Osmotic diuresis of glucose will cause further removal of water and electrolytes from the blood resulting in potentially fatal dehydration, tachycardia and hypotension.
Individuals who follow a low-carbohydrate diet will also develop ketosis, sometimes called nutritional ketosis, but the level of ketone body concentrations are on the order of 0.5-5 mM whereas the pathological ketoacidosis is 15-25 mM.
As the mainstream diet is so high in carbohydrate that ketosis is rarely seen without starvation or ketoacidosis, many practitioners mistake well regulated nutritional ketosis for pathological ketoacidosis.
What is ketoacidosis?
Ketoacidosis is a life-threatening condition that must be immediately addressed. Not to be confused with ketosis.
Two out of three types of ketone bodies are acidic, and, if levels of these ketone bodies are too high, the pH of the blood drops, resulting in ketoacidosis.
Ketoacidosis is known to occur in untreated type I diabetes (diabetic ketoacidosis): when a type 1 diabetic suffers a biological stress event (sepsis, heart attack, infection) or fails to administer enough insulin they may suffer the pathological condition ketoacidosis.
Liver cells increase metabolism of fatty acids into ketones and glucose via glycogenolysis in an attempt to supply energy to peripheral cells which are unable to transport glucose in the absence of insulin.
The resulting very high levels of blood glucose and ketone bodies lower the pH of the blood and trigger the kidneys to attempt to excrete the glucose and ketones. Osmotic diuresis of glucose will cause further removal of water and electrolytes from the blood resulting in potentially fatal dehydration, tachycardia and hypotension.
Ketoacidosis is also known to occur in alcoholics after prolonged binge-drinking without intake of sufficient carbohydrates (alcoholic ketoacidosis).
Less commonly, some patients with poorly controlled type 2 diabetes may have detectable levels of plasma ketones without significant acidosis.
Individuals who follow a low-carbohydrate diet, will develop ketosis, sometimes called nutritional ketosis, but the level of ketone body concentrations are on the order of 0.5-5 mM whereas the pathological ketoacidosis is 15-25 mM.
What are ketones?
Ketone bodies (ketones) are three water-soluble compounds that are produced as by-products when fatty acids are broken down for energy in the liver.
Two of the three are used as a source of energy in the heart and brain while the third (acetone) is a waste product excreted from the body. In the brain, they are a vital source of energy during fasting. Although termed “bodies”, they are dissolved substances, not particles.
Ketone bodies can be used for energy. Ketone bodies are transported from the liver to other tissues, where acetoacetate and beta-hydroxybutyrate can be reconverted to acetyl-CoA to produce energy, via the citric acid cycle.
The heart preferentially utilizes fatty acids for energy under normal physiologic conditions. However, under ketotic conditions, the heart can effectively utilize ketone bodies for energy.
The brain gets a portion of its energy from ketone bodies when glucose is less available (e.g., during fasting, strenuous exercise, low carbohydrate, ketogenic diet and in neonates).
How does our body use ketones?
In the event of low blood glucose, as it is the case in ketogenic diets, most other tissues have additional energy sources besides ketone bodies (such as fatty acids), but the brain has an obligatory requirement for some glucose.
After the diet has been changed to lower blood glucose for 3 days, the brain gets 25% of its energy from ketone bodies. After about 4 days, this goes up to 70% (during the initial stages the brain does not burn ketones, since they are an important substrate for lipid synthesis in the brain).
Furthermore, ketones produced from omega-3 fatty acids may reduce cognitive deterioration in old age.
