There are safer sugar substitutes that can certainly prove helpful to one trying to cut back on sugar intake, which isn't good for the diabetes or the kidney issures. The safest alternative is stevia. It can be found in most grocery stores under the name Sweet Leaf. It can also be found in supplement and health food stores. Of all the alternatives out there, this one is rated the safest by natural health experts. And, of course, since it's also approved by the FDA, conventional health experts don't have a problem with this one either.
You can even buy stevia in its native form at a place that sells medicinal types of herbs in bulk or places that sell a lot of bulk teas. If you use this form, you just combine it with whichever tea you make. If your father likes tea, that is. I didn't like this form with coffee, but it's pretty good for tea. I have even seen the green leaves ground to powder form in one store I've been in.
But, of course, the easiest for people to use is the concentrated stevia powder that usually comes in a little shaker.
If one is not allergic to birch, xylitol is supposed to be a safe alternative, too. But, beware of xylitol if you have pets. Xylitol is known to be toxic to pets. Dogs don't know it's poison to them and they will eat it.
Tropicana slim contains aspartame. The U.S. F.D.A. has certified aspartame as being safe for use by diabetics. That being said, there is some evidence that aspartame may be harmful, especially in large quantities. The controversy has used up megabytes of space on the internet with rumors of political payoffs to permit approval. I use products containing aspartame ocasionally because I enjoy sweet things, and the alternative (sugar) is worse. Like everything else in life, the keyword is "moderation". I tend to go along with the F.D.A. Then again, I still believe in Santa Claus too.
What do you mean by "low sugar." Do you mean a "sugar substitute?"