This info has been borrowed from here.
Insulin = Storage.
To understand how ketones are produced, it is first important to note briefly the role of insulin. When carbohydrates (i.e., cake, cookies, rice, fruit, oatmeal, etc.) are consumed, the pancreas releases insulin due to the elevation in blood glucose (sugar) levels. Insulin is a hormone that provides a signal for tissues to take up the excess blood glucose; the glucose is then either stored as glycogen or converted to and stored as fat. Chronically elevated glucose levels circulating in the bloodstream are harmful and therefore, insulin protects our body from glucose-related damage. However, when insulin levels are even slightly elevated, stored fat cannot be broken down and used for energy. Also, dietary fat will be stored.
Carbohydrate-restriction = Breakdown.
When carbohydrates are restricted in the diet due to fasting or a very low-carbohydrate diet, insulin release from the pancreas reduces substantially. This means that the body is not in a state of storage and therefore, stored fuel supplies like glycogen and fat can be broken down for energy. Once glycogen is depleted, usually after the 1st or 2nd day of carbohydrate-restriction, fatty acids are heavily relied upon to fuel the tissues. The brain, however, cannot directly use fatty acids for energy. This is where ketone bodies come into play!
Ketone bodies are natural compounds formed in the liver and include β-hydroxybutyrate, acetoacetate, and acetone. Similar to carbohydrates and fats, ketone bodies can provide energy for our cellular needs. They are produced in the liver when 1) glucose levels are low and the pathway that breaks down glucose slows down, and 2) high levels of fatty acids are available either from dietary fat or fat stores. Fatty acids can be broken down completely to provide energy directly to certain tissues or they can be broken down partially and transported to the liver. In the liver, these partially broken down fatty acids are then converted into ketone bodies through a pathway called ketogenesis.
Ketone bodies are water soluble unlike fatty acids, so they travel easily through the bloodstream to reach other tissues to be used for fuel. The brain uses ~100% glucose for energy when carbohydrate is present in the diet. However, when ketones are present, the brain can derive up to 60% of its energy directly from ketone bodies. The liver can convert substrates like proteins into glucose (i.e., gluconeogenesis) which can then fuel the other 40% of the brain’s energy during carbohydrate-restriction. All cells have the capacity to use ketone bodies, except liver and red blood cells, however some cells prefer ketones. Besides the brain, the heart and intestines also prefer to use ketone bodies for fuel.
The production and utilization of ketone bodies is thought to be a protective mechanism during times of famine as they increased survival time in starving individuals by providing a non-dietary source of energy. In addition to providing a cellular energy, ketones have a plethora of associated health benefits. Some benefits include (but are not limited to):
– Regulated energy levels
– Reduced oxidative stress and inflammation
– Reduced anxiety and depression
– Improvements in conditions such as epilepsy, Parkinson’s disease, Alzheimer’s disease, polycystic ovary syndrome, diabetes, obesity, cardiovascular disease, and cancer
– Improved body composition
Individuals may elevate circulating ketone bodies by fasting long-term or chronically restricting dietary carbohydrates, as mentioned above. If those ketone-producing strategies are not feasible to maintain as a lifestyle, ketones may also be consumed in order to elevate blood ketone levels. These are called “exogenous ketones” because they are made outside of the body whereas “endogenous ketones” are made inside the body in the liver. Studies have shown success with using exogenous ketones as a therapy for certain conditions in infants and adults. Ketosis, or elevated ketone levels, has become a hot topic in the nutrition, health, and athletic performance fields, and rightfully so. With the positive outcomes that both a very low carbohydrate, ketogenic diet and exogenous ketones are demonstrating, researchers are hopping on board to study how ketone bodies affect various aspects of health and human performance. It is an interesting decade for nutrition, as ideas on “good nutrition” seem to be dramatically shifting and the shift seems to be in favor of carbohydrate-restriction due to the associated ketone body production.
Carbohydrate consumption causes blood sugar levels to rise, subsequently raising insulin levels. Insulin prevents fats cells from entering the bloodstream to be used for energy, so it remains stored in the body. When you lower your intake of carbohydrates, blood sugar and insulin levels drop, causing your body to look for an alternative energy source. Excess glucose that has been converted to glycogen is depleted after 1-2 days of a carb restricted diet, then it turns to fat storage. Entering the metabolic state known as ketosis, your body begins to utilize ketones, the energy source produced by the liver as it breaks down fat. To maintain a ketogenic diet is done so with a HIGH FAT, low carbohydrate diet. This can be difficult for some, so the supplementation of exogenous ketones helps you maintain a higher level of ketones in your body!