Why can’t we convert fat to glucose?

As evident by many sugar-laden soda pop “potbellies” of North America, lipogenesis can obviously occur from drinking and eating too much sugar (1). Wouldn’t it be just grand to reverse the process and be able to lose all that fat via gluconeogenesis? Unfortunately mammals do not have the ability to synthesize glucose from fats (1).

The fact is that once glucose is converted to acetyl coA there is no method of getting back to glucose. The pyruvate dehydrogenase reaction that converts pyruvate to acetyl CoA is not reversible (1p252). Because lipid metabolism produces acetyl CoA via beta-oxidation, there can be no conversion to pyruvate or oxaloacetate that may have been used for gluconeogenesis (1p252). Further, the two carbons in the acetyl CoA molecule are lost upon entering the citric acid cycle (1p252). Thus, the acetyl CoA is used for energy (1p252).

There are some fatty acids that have an odd number of carbon atoms that can be converted to glucose, but these are not common in the diet (1p253). Maybe they should be made more common. Do they taste good?

Reference List

1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.

Published by David Despain, MS, CFS

David is a science and health writer living on Long Island, New York. He's written for a variety of publications including Scientific American, Outside Online, the American Society for Nutrition's (ASN) Nutrition Notes Daily, and Institute of Food Technologists' (IFT) Food Technology magazine and Live! blog. He's also covered new findings reported at scientific meetings including Experimental Biology, AAAS, AOCS, CASW, Sigma Xi, IFT, and others on his personal blog "Evolving Health." David is also an active member of organizations including the National Association of Science Writers (NASW), the American Association for the Advancement of Science (AAAS), the American Society for Nutrition, the Institute of Food Technologists, and the National Audubon Society. David has a master's degree in human nutrition from the University of Bridgeport, and a bachelor's degree in English from University of Illinois at Springfield. He also earned his Certified Food Scientist credential from the Institute of Food Technologists.

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