[h=2]What makes a ketogenic diet[/h]
Scientists are still trying to establish exactly why and how keto diets lead to beneficial therapeutic outcomes, but the “what” of the matter is well understood.
Simply put theres 2 possible sources of fuel for most all cellular functions which are fat and glucose.
Though cellular respiration which is "energy production in the presence of oxygen" using glucose has a weakness: The body can only bank about 1,000–1,600 calories of excess carbohydrate as glycogen—the storage form of glucose. Any excess glucose beyond that is converted via lipogenesis into fat and is stored. On the other hand, either dietary or stored fat can fuel cellular respiration using ketone bodies (a byproduct of the breakdown of fatty acids in the liver). Since many of us have too much of the latter and ready access to the former, fat-as-fuel is in plentiful supply. The advantage of metabolizing stored fat for the overweight and obese is obvious.
Once the body’s glucose and glycogen stores are depleted, ketosis begins, and the body uses stored and/or dietary fat as energy. Generally, carbohydrate consumption must be below 50–60 g/day for ketosis to begin, although each person’s metabolic requirement is unique. The popular and well-studied Atkins diet, which is a type of keto diet, calls for no more than 20 g of carbohydrate/day during its initial phase. To put that in perspective, there are about 7 g of carbohydrate in 100 g of raw broccoli and 31 g of carbohydrate in 100 g of cooked pasta. (See Table 1 for the macronutrient ranges of ketogenic diets.)
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</tbody>Likewise, protein must be held at moderate levels—generally between 15–20% of total daily calories—because the liver will convert as much as 60% of excess protein into glucose via gluconeogenesis, thus stopping ketosis. Fats from sources such as butter, coconut oil, and extra virgin olive oil make up the remainder of the keto diets macronutrient equation (usually between 70–85% of daily calories).
Although the body needs small amounts of glucose to function, dietary carbohydrate in and of itself is not an essential nutrient. When ketosis begins, fat—whether stored or consumed—becomes the primary metabolic fuel in the form of ketone bodies (KBs). The three KBs produced by the liver from fatty acids are acetone, acetoacetic acid, and β-hydroxybutyric acid (BHB). Acetoacetate and BHB can be converted into acetyl-CoA and burned for energy through the citric acid cycle. Acetone can be converted into pyruvate, although it generally is excreted as waste; in some circumstances, it can be metabolized into glucose. The heart favors the use of fatty acids for energy in normal conditions, and it has no problem using KBs under ketotic conditions. The brain requires some glucose under both normal and ketotic conditions; this is readily produced by the liver in ketosis through gluconeogenesis using substrates such as pyruvate, lactate, glycerol, and glucogenic amino acids.
Clearly, the biochemistry of keto diets is much more complicated than this bare-bones description suggests. The focus of this article, however, is on research regarding therapeutic uses of keto diets and not on the cellular mechanisms at play.
Scientists are still trying to establish exactly why and how keto diets lead to beneficial therapeutic outcomes, but the “what” of the matter is well understood.
Simply put theres 2 possible sources of fuel for most all cellular functions which are fat and glucose.
Though cellular respiration which is "energy production in the presence of oxygen" using glucose has a weakness: The body can only bank about 1,000–1,600 calories of excess carbohydrate as glycogen—the storage form of glucose. Any excess glucose beyond that is converted via lipogenesis into fat and is stored. On the other hand, either dietary or stored fat can fuel cellular respiration using ketone bodies (a byproduct of the breakdown of fatty acids in the liver). Since many of us have too much of the latter and ready access to the former, fat-as-fuel is in plentiful supply. The advantage of metabolizing stored fat for the overweight and obese is obvious.
Once the body’s glucose and glycogen stores are depleted, ketosis begins, and the body uses stored and/or dietary fat as energy. Generally, carbohydrate consumption must be below 50–60 g/day for ketosis to begin, although each person’s metabolic requirement is unique. The popular and well-studied Atkins diet, which is a type of keto diet, calls for no more than 20 g of carbohydrate/day during its initial phase. To put that in perspective, there are about 7 g of carbohydrate in 100 g of raw broccoli and 31 g of carbohydrate in 100 g of cooked pasta. (See Table 1 for the macronutrient ranges of ketogenic diets.)
| TABLE 1. Macronutrient ranges and total grams for ketogenic diets | ||
| Macronutrient | % of calories | Total grams* |
| Dietary fat | 70–85% | 178 g |
| Protein | 15–20% | 75 g |
| Carbohydrate | 5–10% | 25 g |
| *Based on 2,000 calories/day with 80% fat, 15% protein, 5% carbohydrate |
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Although the body needs small amounts of glucose to function, dietary carbohydrate in and of itself is not an essential nutrient. When ketosis begins, fat—whether stored or consumed—becomes the primary metabolic fuel in the form of ketone bodies (KBs). The three KBs produced by the liver from fatty acids are acetone, acetoacetic acid, and β-hydroxybutyric acid (BHB). Acetoacetate and BHB can be converted into acetyl-CoA and burned for energy through the citric acid cycle. Acetone can be converted into pyruvate, although it generally is excreted as waste; in some circumstances, it can be metabolized into glucose. The heart favors the use of fatty acids for energy in normal conditions, and it has no problem using KBs under ketotic conditions. The brain requires some glucose under both normal and ketotic conditions; this is readily produced by the liver in ketosis through gluconeogenesis using substrates such as pyruvate, lactate, glycerol, and glucogenic amino acids.
Clearly, the biochemistry of keto diets is much more complicated than this bare-bones description suggests. The focus of this article, however, is on research regarding therapeutic uses of keto diets and not on the cellular mechanisms at play.
