Metabolic pathways
I’ve been meaning for a while to write something on this NY Times article asking if sugar is toxic. The basic gist is that sucrose (table sugar) is broken down into two sugars, glucose and fructose. Glucose feeds right into the glycolysis series and is therefore metabolized in any cell. Fructose, however, has to be processed by the liver, and its byproducts can go into any number of metabolic pathways. When there is a lot of fructose to process, the byproducts promote fat production, which can lead to fatty liver, insulin insensitivity, cardiovascular disease and cancer. Thus the question, “Is sugar toxic?”
The problem with this sort of question is that it totally ignores the biochemical realities of the body. I’ve been helping my daughter with high school chemistry and reviewing Le Chatelier’s principle, which is that a chemical equilibrium will shift according to changes in reactants or products. The body’s metabolic pathways are a complex, interlocking, massively buffered system that allows us to thrive with all sorts of shifts in food supply. The buildup of some fructose biproducts will shift chemical equilibriums and funnel those chemicals into pathways where they can be disposed. The buildup of fructose biproducts only becomes a problem if there is a lot of fructose to deal with and a lot of other calorie rich foods that block those disposal pathways. If calorie consumption is light, the body will utilize fructose very well and it will not be toxic. A lot of water is toxic and can kill you. A lot of alcohol in the blood is toxic, but if you have every been working really hard on little food and then chug a beer you will hardly feel the effects, because the body metabolizes the ethanol immediately for energy. To call sugar toxic in all situations is an overstatement.