Damage Occurs any time you take in more sugar than your cells need for energy at any moment in time.

See, the thing is, even if your insulin production and sensitivity is all in perfect working order, if the cell's energy stores are full, they won't take in more sugar.  If you consume sugar without burning off the stored energy, your cells won't take more in and it will circulate in your bloodstream doing damage and then get taken back into the liver for storage which also causes damage. 

Much of the damage is caused by Glycation, a process in which protein or fat molecules in your arteries  organs and other tissues bond to simple sugar molecules creating Advanced Glycation End products (AGEs) which are implicated in aging, heart disease and diabetes. It causes a loss of elasticity in skin and hardens arteries.  

The sugar your cells can't take in keeps circulating around in your bloodstream doing damage until it gets back to the liver where it gets turned to triglycerides which raise your LDL cholesterol.  Especially the small particle LDL that can penetrate and damage arteries.  And then excess triglycerides are stored in the liver causing fatty liver disease.  Children are now developing non-alcoholic fatty liver disease, something that used to be rare even for adults. 

In addition to all this, excess sugar reduces insulin sensitivity, increases inflammation levels and stimulates excess hormone production. Your body will try releasing more insulin hoping to get your cells to take in the sugar. 

How much sugar your cells can take in varies from person to person depending on activity level, muscle mass, the consumption of nutrients that help the body manage sugar and much more. But the bottom line is that if you are going to eat or drink added sugar, you need to be up and moving around burning energy.  

Note:  The CDC recommends you limit it to 25 grams per day. There's 39 grams of sugar from HFCS in one can of Coke. If we got our sugar only from fruits and vegetables like we are meant to, most people would consume about 15 grams per day.