Low Carbohydrate Diets

There is no established definition of what constitutes a low carbohydrate diet beyond the idea that they all have some type of restriction on carbohydrate intake. Therefore I classify low carbohydrate diets as "Carbohydrate Optimization Diets", "Non-Ketogenic Low Carbohydrate Diets", "Ketogenic Diets", and "Extreme Calorie Restriction Diets", as well as the baseline "Standard American Diet". The specific diets can then be mapped into these categories.

1 Low Carbohydrate Classifications

• Standard American Diet (SAD). This is the baseline from which the diets can generally be compared. The SAD is generally high in carbohydrates, and includes carbohydrate sources such as refined sugars and refined grains.
• Carbohydrate Optimization Diets. This is a broad category of diets that don't restrict the overall quantity of carbohydrate, but do restrict particular types of carbohydrate. Examples would be Paleolithic diets, and nutrient timing.
• Non-Ketogenic Low Carbohydrate Diets (NKLCD). A NKLC diet restricts overall carbohydrate level, typically to around 50-150g of net carbohydrate, but does not elevate ketone levels sufficiently to be considered a Ketogenic Diet. A diet that restricts net carbohydrate intake to below 50g may still be Non Ketogenic if protein intake is not also sufficiently restricted.
• Ketogenic Low Carbohydrate Diets (KLCD). A Ketogenic Diet restricts both carbohydrate and protein intake so that the body metabolizes fat to produce ketones. There is no established definition of what level of ketones are required for a diet to be considered ketogenic. (Fasting ketone levels are typically ~0.3 on the SAD. Also, because it takes time to adjust to a ketogenic diet, I do not consider a diet to be a 'ketogenic diet' even if it elevates ketone levels for less than two weeks. A ketogenic diet should only be started under medical supervision. A Ketogenic diet is sometimes referred to as a Low Carbohydrate Ketogenic Diet or LCKD.
• Extreme Calorie Restriction Diets. These diets are intended to treat severe obesity by dramatically reducing calorie intake.

1.1 Low Carbohydrate Diets

The table below maps some specific diets into the classifications described above.

Diet	SAD	Carbohydrate Optimization	NKLCD	KLCD	ECR
Food Avoidance		Yes	Possible
Slow Carb	Possible	Possible	Possible
Nutrient Timing	Possible	Possible
Paleolithic		Yes	Possible	Possible
Atkins			Yes	Possible
High Protein	Possible	Possible	Yes
Cyclic Ketogenic Diet (CKD)			Yes	Possible
Targeted Ketogenic Diet (TKD).			Possible	Possible
MCT Diet			Possible	Possible
Modified Atkins Diet			Possible	Possible
Ketogenic Ratio Diet				Yes
Fasting					Yes

• Standard American Diet (SAD). This is the baseline from which the diets can generally be compared. The SAD is generally high in carbohydrates, and includes carbohydrate sources such as refined sugars and refined grains.
• Food Avoidance Diets. There are a number of dietary modifications that avoid the specific types of food. Examples would be a gluten-free diet, or diet that avoids sugars such as fructose. These specific Food Avoidance Diets can be combined with other types of diet. For instance, a Low Glycemic Index Diet could also be gluten-free.
• Low Glycemic Index Diet (Slow carb diet). This approach limits carbohydrate intake based on their Glycemic Index. A slow carb diet provides a relatively normal percentage of calories as carbohydrate, but avoids any high Glycemic Index foods such as those that include refined flour or sugars. (Note that this diet is different from the Low Glycemic Index Treatment discussed below.)
• Nutrient Timing. The Nutrient Timing is similar to the Slow Carb diet, but uses high Glycemic Index carbohydrates during and immediately after exercise, then only low Glycemic Index foods the rest of the time.
• Paleolithic Diets. There are a number of diets that aim to re-create the food intake of our caveman ancestors, whose food sources predate the birth of agriculture. Because our ancestors lived in many different geographical areas that provided radically different food sources, there is some variation in what is considered a Paleolithic diet. However, Paleolithic diets always avoid cereals and grains, as well as refined sugars, dairy products. Some studies have estimated the modern hunter gatherer societies get 22–40% of their energy from carbohydrate sources. However, modern interpretations of the Paleolithic diet can vary widely in their carbohydrate intake, and some can be ketogenic (see below for details.)
• Atkins Diet. The Atkins diet is probably the best-known low carbohydrate diet. This diet has four phases, and the initial "induction phase" can be a Ketogenic Diet, but overall the Atkins diet does not maintain elevated blood Ketones.
• High Protein Diet. A high protein diet is one where the protein intake is significantly above the common or recommended levels. A high protein diet could include either a high or a low carbohydrate intake, but even with carbohydrate restriction a high protein diet will not be ketogenic as some of the excess protein will be converted to glucose.
• Targeted Ketogenic Diet (TKD). This is a variant of the ketogenic diet that includes carbohydrates before, during, or immediately after exercise. It is described in Lyle McDonald's book "The Ketogenic Diet", but I am not aware of any scientific studies that evaluate it. The goal of the TKD is to take carbohydrates to support effective training, but without interrupting ketosis. There is one study that has shown that 50g of glucose immediately before or after a 13 mile/20 Km run in 90 minutes did not change subsequent ketosis.
• Cyclic Ketogenic Diet (CKD). Like the Targeted Ketogenic Diet, this diet also comes from Lyle McDonald's book. As the name suggests, this TKD cycles between periods of a ketogenic diet with periods of high carbohydrate intake. McDonald suggests 5-6 days of the ketogenic diet and 1-2 days of a high carbohydrate diet, although he indicates that other periods could be used. As McDonald acknowledges, there is no evidence to indicate how this cycling between ketogenic and non-ketogenic will affect Ketoadaptation. More importantly, it is unclear how the CKD might change the Health Risks of the Ketogenic Diet.
• MCT Diet. This is a variant of the traditional diet that uses Medium Chain Triglycerides (MCTs) which produce more ketones than other oils. The MCD Diet is typically only used for the treatment of epilepsy.
• Modified Atkins Diet (MAD). The MAD started by accident, when a child was put onto the Atkins diet prior to starting the traditional Ketogenic Ratio Diet, and their seizures stopped. The MAD is similar to the induction phase of the Atkins diet, though children are allowed only 10 grams/day of carbohydrate rather than the 20 grams/day allowed for adults.
• Low Glycemic Index Treatment (LGIT). The LGIT restricts the carbohydrate intake to only those foods with a Glycemic Index of less than 50. However, the LGIT is more than just restricting the glycemic index, and requires a fat intake of 60% with a Ketogenic Ratio of 1:1. The LGIT is similar to MAD, but allows 40-60 grams/day of carbohydrates.
• Ketogenic Ratio Diet. The Ketogenic Ratio is commonly used to construct a diet to treat drug resistant epilepsy. The ketogenic diet measures the ratio of grams of fat to the grams of protein plus Net Carbohydrates. For example a 4:1 diet has 4 grams of fat to each gram of carbohydrate or protein. However, this ratio is slightly misleading, as there are other constraints on the diet. By tightly controlling the overall calories and protein intake in addition to the ratio, carbohydrate intake is indirectly tightly controlled.
• Protein Sparing Modified Fast (PSMF). The use of complete fasting to reduce body fat in the severely obese can be effective, but also tends to result in unwanted loss of muscle. By supplementing the fast with a small amount of protein, the diet can still result in rapid weight loss while sparing muscle. A PSMF should only be used under medical supervision as it can be dangerous and people have died from badly formulated PSMF.
• Fasting. Complete fasts are sometimes used to reduce body fat in the severely obese. Many of the studies of ketosis come from studies of fasting subjects.
• Starvation. This is not actually a diet so much as a condition. During extreme calorie intake diets the body will burn the stores of body fat and produce ketones. However, once those body fats become depleted then the body will change to burning the protein from muscle and other tissues. At this point ketosis will end and the protein will be converted to glucose. This is sometime seen in children on the Ketogenic diet who have insufficient body fat; if they get too few calories from fat they may drop out of ketosis and suffer breakthrough seizures.

2 See Also

• The classifications and types of Low Carbohydrate Diet.
• An introduction to the Ketogenic Diet.
• My experiences with ultrarunning on the Ketogenic Diet
  • How the Ketogenic Diet can be used for the treatment and management of disease.
    • Using the Ketogenic Diets to mitigate and treat Epilepsy
    • How Ketogenic Diets might help with Cancer
    • A look at the possible mechanisms of action of the Ketogenic Diet
  • Health Risks of the Ketogenic Diet
    • Health Checks for the Ketogenic Diet
    • Supplements for the Ketogenic Diet
  • The time frame and changes that occur with Ketoadaptation
  • What are Ketones
    • How to measure Ketones
    • What ketone levels to aim for
  • The pros and cons of the Ketogenic Diet for athletes
    • The Science of Ketogenic Exercise
  • The Types of Ketogenic Diet
    • The "traditional" Ketogenic Diet based on the Ketogenic Ratio
      • The ways the Ketogenic Ratio can be calculated
        • The different definitions of Net Carbohydrates
    • Low Glycemic Index Treatment
    • MCT Diet
      • MCT
    • Modified Atkins Diet (M.A.D.)
• My Ketogenic Recipes
• Non-Ketogenic Low Carbohydrate Diets