Well, a 16oz. (grande) non-fat latte has about 130 calories. Only four of those calories are from the espresso shots, and the rest is from the skim milk. Sugar-free syrups are generally considered calorie-free, but even if you figure 1 calorie per shot of syrup, you're still only talking about 3 calories there. So, it's the milk in the latte that's bringing in the extra calories.

If you're concerned about artificial sweeteners, you could switch to a plain non-fat latte. Or, you could drop the milk and sweeteners altogether and drink straight espresso, an Americano (espresso + water), or just brewed coffee.

When I wanted to get rid of the extra calories in my non-fat latte, I switched my drink of choice to the Americano (with a single pump of sugar-free hazelnut syrup) and about a tablespoon of half-and-half on occasion. The half-and-half is ~20 calories per tablespoon. Creamy goodness for my coffee, but way fewer calories than in all of the skim milk used to make a latte.