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How Fat Is Converted To Glucose?

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Science And Nutrition :: You Are What You Ate

Over two thousand years ago, Hippocrates theorized that the body was composed of four fluids or humours including blood, phlegm, choler (yellow bile) and black bile (melancholy). Avicenna later suggested in the ninth century that these humours were derived from the process of digestion and so classified them as well as humans and all foods as hot/moist, hot/dry, cold/moist and cold/dry. Similarly, in ancient China body fluids identified resembled those put forward by Hippocrates. Additionally, the Chinese classified human characteristics, as well as foods, into yin and yang. Indian traditional medicine (ayurveda) categorizes people into three doshas or humours with their corresponding characteristics: vata (active and enthusiastic although a worrier), pitta (sharp intellectual, with a tendency to become irritable under stress) and kapha (balanced and conservative). All of these systems make a reference to the importance of balancing the internal environment of the body and, while their outlook varied, they coincide in the fact that illness was regarded as an imbalance of these components. The human body is amazing in how it protects itself and preserves life. It is indeed true tha Continue reading >>

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Popular Questions

  1. manohman

    Why can't fat be converted into Glucose?

    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?

  2. Czarcasm

    manohman said: ↑
    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?
    Click to expand... Both glucose and fatty acids can be stored in the body as either glycogen for glucose (stored mainly in the liver or skeletal cells) or for FA's, as triacylglycerides (stored in adipose cells). We cannot store excess protein. It's either used to make other proteins, or flushed out of the body if in excess; that's generally the case but we try to make use of some of that energy instead of throwing it all away.
    When a person is deprived of nutrition for a period of time and glycogen stores are depleted, the body will immediately seek out alternative energy sources. Fats (stored for use) are the first priority over protein (which requires the breakdown of tissues such as muscle). We can mobilize these FA's to the liver and convert them to Acetyl-CoA to be used in the TCA cycle and generate much needed energy. On the contrary, when a person eats in excess (a fatty meal high in protein), it's more efficient to store fatty acids as TAG's over glycogen simply because glycogen is extremely hydrophilic and attracts excess water weight; fatty acids are largely stored anhydrously and so you essentially get more bang for your buck. This is evolutionary significant and why birds are able to stay light weight but fly for periods at a time, or why bears are able to hibernate for months at a time. Proteins on the other hand may be used anabolically to build up active tissues (such as when your working out those muscles), unless you live a sedentary lifestyle (less anabolism and therefore, less use of the proteins). As part of the excretion process, protein must be broken down to urea to avoid toxic ammonia and in doing so, the Liver can extract some of that usable energy for storage as glycogen.
    Also, it is worth noting that it is indeed possible to convert FA's to glucose but the pathway can be a little complex and so in terms of energy storage, is not very efficient. The process involves converting Acetyl-CoA to Acetone (transported out of mitochondria to cytosol) where it's converted to Pyruvate which can then be used in the Gluconeogenesis pathway to make Glucose and eventually stored as Glycogen. Have a look for yourself if your interested: http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002116.g003/originalimage (and this excludes the whole glycogenesis pathway, which hasn't even begun yet).
    TLDR: it's because proteins have no ability to be stored in the body, but we can convert them to glycogen for storage during the breakdown process for excretion. Also, in terms of energy, it's a more efficient process than converting FA's to glycogen for storage.

  3. soccerman93

    This is where biochem comes in handy. Czarcasm gives a really good in depth answer, but a simpler approach is to count carbons. The first step of gluconeogenesis(formation of glucose) requires pyruvate, a 3 carbon molecule. Acetyl Co-A is a 2 carbon molecule, and most animals lack the enzymes (malate synthase and isocitrate lyase) required to convert acetyl co-A into a 3 carbon molecule suitable for the gluconeogenesis pathway. The ketogenic pathway is not efficient, as czarcasm pointed out. While acetyl co-A can indeed be used to form citric acid intermediates, these intermediates will be used in forming ATP, not glucose. Fatty acid oxidation does not yield suitable amounts of pyruvate, which is required for gluconeogenesis. This is part of why losing weight is fairly difficult for those that are overweight, we can't efficiently directly convert fat to glucose, which we need a fairly constant supply of. Sorry, that got a little long-winded

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Fat-to-glucose Interconversion By Hydrodynamic Transfer Of Two Glyoxylate Cycle Enzyme Genes

Fat-to-glucose interconversion by hydrodynamic transfer of two glyoxylate cycle enzyme genes 1Department of Nutrition and Food Sciences, Physiology and Toxicology, University of Navarra, Pamplona, Spain 2Laboratory of Animal Physiology and Nutrition, School of Agronomy, Public University of Navarra, Pamplona, Spain Received 2008 Sep 29; Accepted 2008 Dec 10. Copyright 2008 Cordero et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The glyoxylate cycle, which is well characterized in higher plants and some microorganisms but not in vertebrates, is able to bypass the citric acid cycle to achieve fat-to-carbohydrate interconversion. In this context, the hydrodynamic transfer of two glyoxylate cycle enzymes, such as isocytrate lyase (ICL) and malate synthase (MS), could accomplish the shift of using fat for the synthesis of glucose. Therefore, 20 mice weighing 23.37 0.96 g were hydrodinamically gene transferred by administering into the tail vein a bolus with ICL and MS. Continue reading >>

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Popular Questions

  1. manohman

    Why can't fat be converted into Glucose?

    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?

  2. Czarcasm

    manohman said: ↑
    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?
    Click to expand... Both glucose and fatty acids can be stored in the body as either glycogen for glucose (stored mainly in the liver or skeletal cells) or for FA's, as triacylglycerides (stored in adipose cells). We cannot store excess protein. It's either used to make other proteins, or flushed out of the body if in excess; that's generally the case but we try to make use of some of that energy instead of throwing it all away.
    When a person is deprived of nutrition for a period of time and glycogen stores are depleted, the body will immediately seek out alternative energy sources. Fats (stored for use) are the first priority over protein (which requires the breakdown of tissues such as muscle). We can mobilize these FA's to the liver and convert them to Acetyl-CoA to be used in the TCA cycle and generate much needed energy. On the contrary, when a person eats in excess (a fatty meal high in protein), it's more efficient to store fatty acids as TAG's over glycogen simply because glycogen is extremely hydrophilic and attracts excess water weight; fatty acids are largely stored anhydrously and so you essentially get more bang for your buck. This is evolutionary significant and why birds are able to stay light weight but fly for periods at a time, or why bears are able to hibernate for months at a time. Proteins on the other hand may be used anabolically to build up active tissues (such as when your working out those muscles), unless you live a sedentary lifestyle (less anabolism and therefore, less use of the proteins). As part of the excretion process, protein must be broken down to urea to avoid toxic ammonia and in doing so, the Liver can extract some of that usable energy for storage as glycogen.
    Also, it is worth noting that it is indeed possible to convert FA's to glucose but the pathway can be a little complex and so in terms of energy storage, is not very efficient. The process involves converting Acetyl-CoA to Acetone (transported out of mitochondria to cytosol) where it's converted to Pyruvate which can then be used in the Gluconeogenesis pathway to make Glucose and eventually stored as Glycogen. Have a look for yourself if your interested: http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002116.g003/originalimage (and this excludes the whole glycogenesis pathway, which hasn't even begun yet).
    TLDR: it's because proteins have no ability to be stored in the body, but we can convert them to glycogen for storage during the breakdown process for excretion. Also, in terms of energy, it's a more efficient process than converting FA's to glycogen for storage.

  3. soccerman93

    This is where biochem comes in handy. Czarcasm gives a really good in depth answer, but a simpler approach is to count carbons. The first step of gluconeogenesis(formation of glucose) requires pyruvate, a 3 carbon molecule. Acetyl Co-A is a 2 carbon molecule, and most animals lack the enzymes (malate synthase and isocitrate lyase) required to convert acetyl co-A into a 3 carbon molecule suitable for the gluconeogenesis pathway. The ketogenic pathway is not efficient, as czarcasm pointed out. While acetyl co-A can indeed be used to form citric acid intermediates, these intermediates will be used in forming ATP, not glucose. Fatty acid oxidation does not yield suitable amounts of pyruvate, which is required for gluconeogenesis. This is part of why losing weight is fairly difficult for those that are overweight, we can't efficiently directly convert fat to glucose, which we need a fairly constant supply of. Sorry, that got a little long-winded

  4. -> Continue reading
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Conversion Of Carbohydrate To Fat In Adipose Tissue: An Energy-yielding And,therefore, Self-limiting Process.

Conversion of carbohydrate to fat in adipose tissue: an energy-yielding and,therefore, self-limiting process. A theoretical analysis of the energy metabolism associated with the conversion ofglucose to fat is presented. In tissues where the pentose cycle furnishes some ofthe NADPH required for fatty acid synthesis, this conversion is an ATP-yieldingprocess. In rat adipose tissue the maximal rate of glucose conversion to fat can be quantatively predicted on the basis of the tissue's ability to use the ATPwhich is generated in excess during this conversion. The energy-generating natureof this process provides the means for a type of regulation which depends onmetabolic state and which, during fasting, contributes to the sparing ofcarbohydrate. Impairment of lipogenesis in the fasting state is attributed to adecrease in the activity of the malate cycle and to the presence of free fattyacids. However, rather than by inhibiting specific enzymes, it is by virtue oftheir quality as substrates for energy production that free fatty acids and theirCoA derivatives appear to inhibit de novo lipogenesis. The regulatory phenomenadiscussed here may explain the failure of the attempts made to ide Continue reading >>

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Popular Questions

  1. manohman

    Why can't fat be converted into Glucose?

    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?

  2. Czarcasm

    manohman said: ↑
    So the reason cited is that beta oxidation/metabolism of fats leads to formation of acetyl coa, a 2 carbon molecule, and that because of that it cannot be converted back into glucose.
    Why exactly is that the case?
    If Glucogenic amino acids can be converted into citric acid cycle intermediates and then turn back into glucose via gluconeogensis, then why cant Fatty Acids which yield Acetyl Coa. Can't you just have Acetyl Coa enter the citric acid cycle and produce the same intermediates that the glucogenic amino acids creat?
    Click to expand... Both glucose and fatty acids can be stored in the body as either glycogen for glucose (stored mainly in the liver or skeletal cells) or for FA's, as triacylglycerides (stored in adipose cells). We cannot store excess protein. It's either used to make other proteins, or flushed out of the body if in excess; that's generally the case but we try to make use of some of that energy instead of throwing it all away.
    When a person is deprived of nutrition for a period of time and glycogen stores are depleted, the body will immediately seek out alternative energy sources. Fats (stored for use) are the first priority over protein (which requires the breakdown of tissues such as muscle). We can mobilize these FA's to the liver and convert them to Acetyl-CoA to be used in the TCA cycle and generate much needed energy. On the contrary, when a person eats in excess (a fatty meal high in protein), it's more efficient to store fatty acids as TAG's over glycogen simply because glycogen is extremely hydrophilic and attracts excess water weight; fatty acids are largely stored anhydrously and so you essentially get more bang for your buck. This is evolutionary significant and why birds are able to stay light weight but fly for periods at a time, or why bears are able to hibernate for months at a time. Proteins on the other hand may be used anabolically to build up active tissues (such as when your working out those muscles), unless you live a sedentary lifestyle (less anabolism and therefore, less use of the proteins). As part of the excretion process, protein must be broken down to urea to avoid toxic ammonia and in doing so, the Liver can extract some of that usable energy for storage as glycogen.
    Also, it is worth noting that it is indeed possible to convert FA's to glucose but the pathway can be a little complex and so in terms of energy storage, is not very efficient. The process involves converting Acetyl-CoA to Acetone (transported out of mitochondria to cytosol) where it's converted to Pyruvate which can then be used in the Gluconeogenesis pathway to make Glucose and eventually stored as Glycogen. Have a look for yourself if your interested: http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002116.g003/originalimage (and this excludes the whole glycogenesis pathway, which hasn't even begun yet).
    TLDR: it's because proteins have no ability to be stored in the body, but we can convert them to glycogen for storage during the breakdown process for excretion. Also, in terms of energy, it's a more efficient process than converting FA's to glycogen for storage.

  3. soccerman93

    This is where biochem comes in handy. Czarcasm gives a really good in depth answer, but a simpler approach is to count carbons. The first step of gluconeogenesis(formation of glucose) requires pyruvate, a 3 carbon molecule. Acetyl Co-A is a 2 carbon molecule, and most animals lack the enzymes (malate synthase and isocitrate lyase) required to convert acetyl co-A into a 3 carbon molecule suitable for the gluconeogenesis pathway. The ketogenic pathway is not efficient, as czarcasm pointed out. While acetyl co-A can indeed be used to form citric acid intermediates, these intermediates will be used in forming ATP, not glucose. Fatty acid oxidation does not yield suitable amounts of pyruvate, which is required for gluconeogenesis. This is part of why losing weight is fairly difficult for those that are overweight, we can't efficiently directly convert fat to glucose, which we need a fairly constant supply of. Sorry, that got a little long-winded

  4. -> Continue reading
read more close

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