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How Fat Is Converted To Glucose?

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How Fat Cells Work

In the last section, we learned how fat in the body is broken down and rebuilt into chylomicrons, which enter the bloodstream by way of the lymphatic system. Chylomicrons do not last long in the bloodstream -- only about eight minutes -- because enzymes called lipoprotein lipases break the fats into fatty acids. Lipoprotein lipases are found in the walls of blood vessels in fat tissue, muscle tissue and heart muscle. Insulin When you eat a candy bar or a meal, the presence of glucose, amino acids or fatty acids in the intestine stimulates the pancreas to secrete a hormone called insulin. Insulin acts on many cells in your body, especially those in the liver, muscle and fat tissue. Insulin tells the cells to do the following: The activity of lipoprotein lipases depends upon the levels of insulin in the body. If insulin is high, then the lipases are highly active; if insulin is low, the lipases are inactive. The fatty acids are then absorbed from the blood into fat cells, muscle cells and liver cells. In these cells, under stimulation by insulin, fatty acids are made into fat molecules and stored as fat droplets. It is also possible for fat cells to take up glucose and amino acids, w 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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Video by Ulf Smith, MD, PhD, Professor of Internal Medicine, The Lundberg Laboratory for Diabetes Research, Center of Excellence for Cardiovascular and Metabolic Research, Sahlgrenska Academy, Gteborg University, Gteborg, Sweden Produced by the International Chair on Cardiometabolic Risk

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. Christian

    I read conflicting views about whether or not the human body can create glucose out of fat. Can it?

  2. David

    Only about 5–6% of triglyceride (fat) can be converted to glucose in humans.
    This is because triglyceride is made up of one 3-carbon glycerol molecule and three 16- or 18-carbon fatty acids. The glycerol (3/51-to-57 = 5.2–5.9%) can be converted to glucose in the liver by gluconeogenesis (after conversion to dihydroxyacetone phosphate).
    The fatty acid chains, however, are oxidized to acetyl-CoA, which cannot be converted to glucose in humans. Acetyl-CoA is a source of ATP when oxidized in the tricarboxylic acid cycle, but the carbon goes to carbon dioxide. (The molecule of oxaloacetate produced in the cycle only balances the one acetyl-CoA condenses with to enter the cycle, and so cannot be tapped off to gluconeogenesis.)
    So triglyceride is a poor source of glucose in starvation, and that is not its primary function. Some Acetyl-CoA is converted to ketone bodies (acetoacetate and β-hydroxybutyrate) in starvation, which can replace part — but not all — of the brain’s requirement for glucose.
    Plants and some bacteria can convert fatty acids to glucose because they possess the glyoxylate shunt enzymes that allow two molecules of Acetyl-CoA to be converted into malate and then oxaloacetate. This is generally lacking in mammals, although it has been reported in hibernating animals (thanks to @Roland for the last piece of info).

  3. blu potatos

    To be more detailed it is the irreversibly of the reaction carried by Pyruvate dehydrogenase that makes the conversion of the fatty acid chains to glucose impossible. The fatty acids chains are converted to acetyl-CoA.
    Acetyl-CoA to be converted into pyruvate need an enzyme that can do the Pyruvate Dehydrogenase's inverse reaction (in humans there is no such enzyme). Than the pyruvete inside the mitochondria is converted into glucose(gluconeogenesis).

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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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