Since sugar only has 16 calories per teaspoon, is it okay to use one teaspoon of sugar in a cup of tea? Should I use sugar substitute?

That's an interesting question.

For a diabetic there's more to it than the calories.
You always have to consider the carbs.
A teaspoon of sugar and by that amount I mean a measuring teaspoon of sugar has 4.2 carbs.
That's not bad since you don't even have to count that as a carb choice.

I think probably you need to consider these factors before making your choice.
Can you stop at just one teaspoon?
If you use 2 teaspoons or more are you willing to give up a carb choice(s)?

How does your blood sugar react to using sugar?
I think white sugar is considered a simple sugar. So will the amount you use give you a blood sugar spike and then an unpleasant drop later on in the day.
The key here is checking that glucose when you first begin using table sugar.

How do you feel after you've used sugar?
Most of the time sugar makes me feel jittery and not so good.
So I'd rather go with a sugar sub.
It certainly doesn't affect everyone that way.

My choice happens to be spenda.
I trust it and I don't have to worry about how it affects my glucose.
It's also tummy friendly.

I'm not anti sugar.
If you want that teaspoon then I see nothing wrong with it.
As long as it doesn't adversly affect your blood glucose.

Do you really feel the need for sugar. Is there any reason that you can't use a sugar substitute.
there are many sugar substitutes to choose from.

Hi bobbi, I'm thrilled to see someone else posting.
Hope to see you here a lot.

Sometimes I'd just rather use real sugar instead of a sugar substitute. I think you're right that paying attention to the amount I use, as well as what it does to blood sugar levels, is the key here. I may add only 1/2 teaspoon sugar to a cup of tea, so that's really not enough to get excited about.