Fructose Metabolism 101

Dr. Robert Lustig,  Professor of Pediatrics in the Division of   Endocrinology at the University of California, San Francisco, has been a pioneer in decoding sugar metabolism. His work has highlighted some major differences in how different sugars are broken down and used:  

  • After eating fructose, 100 percent of the  metabolic burden rests on your liver. But with glucose, your liver has to break  down only 20 percent.
  • Every cell in your body, including your brain,  utilizes glucose. Therefore, much of it is “burned up” immediately  after you consume it. By contrast, fructose is turned into free fatty acids  (FFAs), VLDL (the damaging form of cholesterol), and triglycerides, which get  stored as fat.
  • The fatty acids created during fructose  metabolism accumulate as fat droplets in your liver and skeletal muscle  tissues, causing insulin resistance and non-alcoholic fatty liver disease  (NAFLD). Insulin resistance progresses to metabolic syndrome and type II  diabetes.
  • Fructose is the most lipophilic carbohydrate. In  other words, fructose converts to activated glycerol (g-3-p), which is directly  used to turn FFAs into triglycerides. The more g-3-p you have, the more fat you  store. Glucose does not do this.
  • When you eat 120 calories of glucose, less than  one calorie is stored as fat. 120 calories of fructose results in 40 calories  being stored as fat. Consuming  fructoseis essentially consuming fat!
  • The metabolism of fructose by your liver  creates a long list of waste products and toxins, including a large amount of  uric acid, which drives up blood pressure and causes gout.
  • Glucose suppresses the hunger hormone  ghrelin and stimulates   leptin, which suppresses your appetite. Fructose has no effect on ghrelin  and interferes with your brain’s communication with leptin, resulting in  overeating.

  If anyone tries to tell you “sugar is sugar,” they are way behind the times. As you can see, there are major differences in how your body processes fructose and glucose. The bottom line is: fructose leads to increased belly fat, insulin resistance, and metabolic syndrome — not to mention the long list of chronic diseases that directly result. And eating sugar may accelerate the aging process itself.