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Why Can't Fat Be Converted To Glucose

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How The Body Uses Carbohydrates, Proteins, And Fats

How the Body Uses Carbohydrates, Proteins, and Fats The human body is remarkably adept at making do with whatever type of food is available. Our ability to survive on a variety of diets has been a vital adaptation for a species that evolved under conditions where food sources were scarce and unpredictable. Imagine if you had to depend on successfully hunting a woolly mammoth or stumbling upon a berry bush for sustenance! Today, calories are mostly cheap and plentifulperhaps too much so. Understanding what the basic macronutrients have to offer can help us make better choices when it comes to our own diets. From the moment a bite of food enters the mouth, each morsel of nutrition within starts to be broken down for use by the body. So begins the process of metabolism, the series of chemical reactions that transform food into components that can be used for the body's basic processes. Proteins, carbohydrates , and fats move along intersecting sets of metabolic pathways that are unique to each major nutrient. Fundamentallyif all three nutrients are abundant in the dietcarbohydrates and fats will be used primarily for energy while proteins provide the raw materials for making hormones 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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