Robert Lustig explains how fructose breaks your cells' energy system. When you eat too much fructose, it raises uric acid, which blocks CPT1a and stops your mitochondria from burning fat. The result: your liver stores fat instead of using it for energy.
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The uric acid inhibits this enzyme here called CPT1a, carnitine palmidoyl transferase 1a, which regenerates carnitine. And carnitine is necessary because it's the shuttle mechanism by which fatty acids get from the outside world into the mitochondria so that they can be beta oxidized, the sum total of which is that beta oxidation goes down with fructose. So the molecule, sugar, dietary sugar, has glucose and fructose. What's the net effect? The net effect is actually inhibition. And this is what Ron Kahn himself said about this study. The most important takeaway of this study is that high fructose in the diet is bad. It's not bad because it's more calories, but because it has effects on liver metabolism to make it worse at burning fat. As a result, adding fructose to the diet makes the liver store more fat. And this is bad for the liver and bad for whole body metabolism. Couldn't agree more.