Cha yen is a dessert that people drink like water. The black tea is free, the ice is free, and then the vendor pours 3 things into it that are anything but. Condensed milk is 130 calories per 40g pour, evaporated milk is another 55, and the sugar syrup is 100. That is 285 calories for a drink that takes 4 minutes to finish and does nothing for hunger. Two a day, which is normal in the hot season, is 600 calories, the same as a plate of khao kha moo.
The Department of Health measured street versions with 13 teaspoons of sugar in one cup, which is why their per cup figure runs higher than most tables. Dietitian figures for a 16 oz glass land between 250 and 350 depending on the shop. The 22 oz size that chains like ChaTraMue sell is closer to 420, and adding pearls pushes it past 450. The colour tells you nothing. A pale glass just means more evaporated milk, not less sugar.
The fix is not to give it up. Cha dam yen, the same tea with sugar but no milk, is about 120 calories. Ordering wan noi (less sweet) drops a standard glass to about 200. The difference between a daily 300 and a daily 200 is 36,500 calories a year, which is roughly 4 to 5kg of body fat for changing 2 words at the counter.