Having discussed the primary metabolic adaptations which occur during ketosis, we can now examine the effects of ketogenic diets on body composition. The first issue to examine is the effect of food intake on ketosis. This will lead into an examination of protein sparing on a ketogenic diet, as well as issues involving weight, water, and fat loss.
The question to be answered is whether a ketogenic diet does in fact cause greater fat loss with less loss of body protein than a more ‘balanced’ diet. Unfortunately, the lack of appropriate studies, as well as a high degree of variability in study subjects, make this a difficult question to answer unequivocally. Issues relating to water loss on a ketogenic diet are discussed as well.
Section 1: Macronutrients and Ketosis
Before discussing how to prevent nitrogen loss during starvation, we need to briefly discuss the effects of different nutrients on the development of ketosis. Both protein and carbohydrate intake will impact the development of ketosis, affecting both the adaptations seen as well as how much of a ‘protein sparing’ effect will occur.
Despite the generally ‘high fat’ nature of the ketogenic diet, or at least how it is perceived, dietary fat intake has a rather minimal effect on ketosis per se. Fat intake will primarily affect how much bodyfat is used for fuel. Although alcohol has been discussed within the context of ketoacidosis, the effects of alcohol intake on the state of ketosis are discussed again here.
The ketogenic ratio
Although its application for ketogenic dieters is somewhat limited, the simplest way to examine the effects of food consumption on ketosis is to look at the equation used to develop ketogenic diets for childhood epilepsy (figure 1).
Figure 1: The ketogenic ratio
Ketogenic K 0.9 fat + 0.46 protein
——————- = —- = ————————————————-
Anti-ketogenic AK 1.0 carbohydrate + 0.1 fat + 0.58 protein Note: Protein, fat and carbohydrates are in grams.
Source: Withrow CD. The ketogenic diet: mechanism of anticonvulsant action. Adv Neurol (1980) 7: 635-642.
This equation represents the relative tendency for a given macronutrient to either promote or prevent a ketogenic state (1). Recalling that insulin and glucagon are the ultimate determinants of the shift to a ketotic state, this equation essentially represents the tendency for a given nutrient to raise insulin (anti-ketogenic) or glucagon (pro-ketogenic).
For the treatment of epilepsy, the ratio of K to AK must be at least 1.5 for a meal to be considered ketogenic (1). Typically, this results in a diet containing 4 grams of fat for each gram of protein and carbohydrate, called a 4:1 diet. More details on the development of ketogenic diets for epilepsy can be found in the references, as they are beyond the scope of this book.
Although this ratio is critically important for the implementation of the ketogenic diet in clinical settings, we will see that it is not as important for the general dieting public.
Each macronutrient is now briefly discussed within the context of the equation in figure 1.
Carbohydrate is 100% anti-ketogenic. As carbohydrates are digested, they enter the bloodstream as glucose, raising insulin and lowering glucagon, which inhibits ketone body formation. In fact, any dietary change that raises blood glucose is anti-ketogenic.
As mentioned iin earlier posts, the brain is the only tissue which requires glucose in amounts of roughly 100 grams per day. If sufficient carbohydrate is consumed to provide this much glucose, the brain will have no need to begin using ketones. Therefore any diet which contains more than 100 grams of carbohydrate per day will not be ketogenic (2). After approximately three weeks, when the brain’s glucose requirements have dropped to only grams of glucose per day, carbohydrates must be restricted even further.
Additionally, from the standpoint of rapidly depleting liver glycogen, the more that carbohydrates are restricted during the first days of a ketogenic diet, the faster ketosis will occur and the deeper the degree of ketonemia. When examining the diet studies, any diet with more than 100 grams of carbohydrates is considered to be non-ketogenic (often called a ‘balanced’ diet) while any diet with less than 100 grams of carbohydrates is ketogenic (2).
Protein has both ketogenic effects (46%) and anti-ketogenic effects (58%). This reflects the fact that 58% of dietary protein will appear in the bloodstream as glucose (3), raising insulin and inhibiting ketogenesis. Note that the insulin response from consuming dietary protein is much smaller than that from consuming dietary carbohydrates. Consequently protein must be restricted to some degree on a ketogenic diet as excessive protein intake will generate too much glucose, impairing or preventing ketosis. Protein also stimulates glucagon release and has some pro-ketogenic effects.
The most critical aspect of protein intake has to do with preventing the breakdown of body protein. By providing dietary protein during starvation, the breakdown of body protein can be decreased or avoided entirely (4). The interactions between protein and glucose intake and protein sparing are the topic of the next section.
Fat is primarily ketogenic (90%) but also has a slight anti-ketogenic effect (10%). This represents the fact that ten percent of the total fat grams ingested will appear in the bloodstream as glucose (via conversion of the glycerol portion of triglycerides) (5,6). If 180 grams of fat are oxidized (burned) per day, this will provide 18 grams of glucose from the conversion of glycerol.
Although alcohol is not represented in the above equation, having no direct effect on ketosis, alcohol intake will have an impact on the depth of ketosis and the amount of body fat used by the body. Excessive alcohol intake while in ketosis can cause runaway acidosis to develop which is potentially very dangerous. Additionally as alcohol intake limits how much FFA can be processed by the liver, calories from alcohol will detract from overall fat loss.
The three macronutrients are carbohydrate, protein and fat. All three nutrients have differing effects on ketosis due to their digestion and subsequent effects on blood glucose and hormone levels. Carbohydrate is 100% anti-ketogenic due to its effects on blood glucose and insulin (raising both). Protein is approximately 46% ketogenic and 58% anti-ketogenic due to the fact that over half of ingested protein is converted to glucose, raising insulin. Fat is 90% ketogenic and ten percent anti-ketogenic, representing the small conversion of the glycerol portion of triglycerides to glucose. While alcohol has no direct effect on the establishment of ketosis, excessive alcohol intake can cause ketoacidosis to occur.