Our body processes glucose more efficiently than it does fructose. Lustig explains this through a tale of two food sources: two slices of white bread versus orange juice. The bread contains 120 calories of glucose, and the juice 120 calories of sucrose.
Of the 120 glucose calories in bread, 80% (or 96 calories) will be used to fuel the body's organs; every cell in the body uses glucose. Said Lustig, "Every living thing on the face of the earth can use glucose because glucose is the energy of life."
The unused 20% goes to the liver, where some will be converted and stored as glycogen for later use, and some will be released into the bloodstream. That stimulates the pancreas to produce insulin, which regulates blood sugar and helps signal the brain that you are full.
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Most of the stored glycogen will get burned off as your body needs it, though a very small amount — Lustig estimates half of one calorie — will be converted to low-density lipoprotein, or "bad" cholesterol. Finally, a tiny bit of the glucose leaves the liver as citrate, and through a series of processes, is turned into fat.
The sucrose from the orange juice, by contrast, is half-glucose and half-fructose — 60 calories of each. Fructose can be processed only by the liver, and cannot be used by other organs, so all 60 calories will be processed there, where it creates toxic byproducts like uric acid. High consumption of sucrose leads to high levels of uric acid, which is associated with several obesity-related diseases such gout and hypertension. In the case of hypertension, uric acid blocks the enzyme in the blood vessels that makes nitric oxide, which is what controls blood pressure. Gout is caused by a build-up of uric acid in the joints.
In his lecture, Lustig cites a University of Texas at San Antonio study of obese adolescents with hypertension; those who were given allopurinol, which treats gout, saw their blood pressure drop to normal, he said.
Next:Sugar is More Fattening Than Fat
In case you haven’t seen it yet, there’s a video on YouTube of a lecture called “Sugar: The Bitter Truth,” delivered by Dr. Robert Lustig, a pediatric endocrinologist at the University of California, San Francisco. The lecture, which runs some 90 minutes and delves into the details of the professor’s clinical observations and research, has been viewed more than a million times to date, and inspired the April 17 New York Times Magazine cover story headlined “Is Sugar Toxic?” We watched it, so you didn’t have to.