The Ketogenic Diet explains the process by which the body forgoes the use of glucose from carbohydrate to the use of free fatty acids (FFA) and ketones for the energy throughout the body. More generally, when a person doesn’t consume carbohydrates in certain amounts, thought to be below 100 grams of carbohydrate per day, determines whether or not a person will be in a state of ketosis. Many dieters are drawn to the ketogenic diet in an effort to burn more fat mass while sparing lean body mass (LBM).
Fasting and the Ketogenic Diet
In many ways, the ketogenic diet attempts to mimic the metabolic state of fasting, the complete absence of food. Both fasting and the ketogenic diet primarily affect the two hormones, insulin and glucagon. Insulin is the body’s “anabolic” storage hormone while glucagon, which can be thought of as insulin’s opposite twin, is the body’s “catabolic” hormone which directs the breaking down of tissue, such as liver glycogen and FFA, for use as energy throughout the body. When carbohydrates are consumed, and to a lesser extent protein, are consumed insulin rises. After feeding, insulin lowers. As insulin lowers glucagon is released throughout the body. The level of insulin relative to glucagon is called the I/G ratio. In the absence of carbohydrates, whether through fasting or the ketogenic diet, glucagon will stay elevated relative to insulin.
Fueling the Body
Under normal dietary conditions glucose, derived from sufficient carbohydrates, is the body’s preferred energy source. As glucose is burned off, the body turns to its fat store and begins to use FFA for fuel for most organs throughout the body. There are a few organs that are unable to use FFA for energy, primarily the brain. Since the brain and few other small organs are unable to use to use FFA for energy, another energy source is needed in the absence of glucose, hence ketones. Ketones are derived from FFA, converted into ketones in the liver and then used to power the brain.
Protein can also be used to power the body. The author notes that for the first few weeks during the ketogenic diet protein requirements remain quite high. This is because there are couple amino acids that can be readily converted into glucose. The reason for this is that brain needs some time to adjust from converting its energy requirements from glucose to ketones. The time it takes for the brain to get used to ketones for fuel is roughly three weeks. After three weeks, protein requirements may be relaxed slightly depending on the weight of the dieter.
So there you have it. All you need to do is stop consuming those insulin spiking carbs. Converting to diet high in protein and fat while keeping carbohydrates to an absolute minimum will keep insulin low, thereby keeping glucagon high. When glucagon is high fuel from FFA is mobilized to be used to power the body. FFA is converted to ketones in the liver to power the brain, heart as well as few other organs. You are now a lean mean fat burning machine. Well…
Complications exist due to the inability of the ketogenic diet to sustain any amount of at least moderately intense exercise. The ketogenic diet may be able to sustain a regimen of brisk walking, but that is about it. Also, assuming the dieter is on a fat loss diet, exercise must accompany the diet. Study after study, over and over again, has determined that no fat loss diet has been sustained successfully without the incorporation of regular exercise.
Glucose and Glycogen
The fate of any carbohydrate, whether from starches, fruits or sugary cookies is used to power the body as glucose or to be stored in the liver and muscles as glycogen. The liver can store roughly about one hundred grams from carbohydrate for stored glycogen in the liver. Remember that the keto threshold is roughly one hundred grams of carbohydrate per day. Muscle glycogen is used to power the muscles in times of stress, or exercise. When glycogen levels in the muscles fall below a certain threshold, exercise becomes severely impaired. Interesting to note as well, when carbohydrates are consumed after exercise, muscle glycogen levels are topped off before liver glycogen begins to store. This matters to those wishing to remain in a state of ketosis as it is the level of liver glycogen that ultimately determines ketosis. Exercise creates a type of carbohydrate “sink.”
Exercise, The SKD, The CKD and The TKD
The Standard (strict) Ketogenic Diet, or SKD, is a diet where the consumption of carbohydrates is limited at all times in order to keep the body in perpetual state of ketosis. Assuming this is the ketogenic diet is being used as aid for fat loss, and even general health more broadly; exercise must be a necessary component to any dietary regimen. The SKD may be able to support brisk walking twenty to thirty minutes, but nothing more. It is a basic physiological fact that carbohydrates will be needed.
The question then becomes how does a dieter support exercise while remaining in a state of ketosis? Energy is still necessary. Two ways discussed in the book are The Cyclical Ketogenic Diet (CKD) and The Targeted Ketogenic Diet. The goal of the CKD is to go five days on the ketogenic diet and then spend two days loading up on carbs. This can easily be done by abstaining from carbs Monday through Friday and then using the weekend to use a carb load to replenish glycogen stores. The author goes into quite a bit of detail regarding the CKD since that is something the author used while he maintained a ketogenic diet. Personally when I’m cutting weight, I like to use used the TKD. I suspect that more common dieters, common dieters not being professional body builders, will be more apt to use the TKD. The gist of the TKD is to only consume carbs around exercise. For example, a dieter may be on a three day split (that simply means the dieter is lifting weights three times per week), that person would consume carb rich sources directly after exercise to replenish glycogen stores. In other words, the dieter would eat three meals per week with carb rich sources while avoiding carbohydrates at all other times. Remember, as stated above, that muscle glycogen will be replenished before liver glycogen and ultimately it is liver glycogen that will determine whether or not a dieter remains in ketosis.
The Ketogenic Diet is a diet whereby the consumption of carbohydrates is minimized to induce a metabolic state of ketosis. Of relevance to dieters, it is thought that ketosis mimics the state of fasting by releasing FFA for use for energy throughout the body. Certain organs, specifically the brain, are unable to use FFA for energy. Therefore, FFA is transported to the liver converted into ketones which are then used to power the brain. It is the fat burning component to the ketogenic diet that draws in many dieters. While the burning of fat from such a dietary strategy is an enticing one, complications still exist. It is well documented that any dietary strategy without the inclusion of exercise is doomed for failure. While FFA can be used to support light exercise such as twenty to thirty minutes of brisk walking, anything more intense will require glycogen, or carbohydrates stored in the liver and muscles. A couple of strategies can be used to replenish while, at least mostly, remaining in a state of ketosis. One is the CKD which involves five days of minimizing carbs followed by a two day carb up. The more practical strategy for the common dieter is the TKD. With the TKD, the dieter consumes carbohydrates only around exercise to replenish glycogen stores while avoiding carbohydrates at meals away from exercise.