What are the negative health effects of sugar substitutes? In
particular, sucralose or Splenda.

http://www.snopes.com/toxins/aspartame.asp

I trust them more than any web site with the word "holistic" in it

Hello. Here is a quote from the book, Natural Cures "They" Don't Want
You to Know About, by Kevin Trudeau:

"Sucruose - Splenda
This is one of the newest, hottest man-made chemical sweeteners. In my
personal opinion, it is very deadly, poisonous and makes you fat. It
was produced so that the food industry could capitalize on the
low-carbohydrate craze. Now, products can have "no carbohydrates" or
"low carbohydrates" and still taste sweet. The problem is that it's
unnatural, it's artificial, and these man-made artificial sweeteners
do in fact increase your appetite, make you depressed, cause all types
of symptoms (including migraine headaches, PMS, depression,
fibromyalgia, allergies), and most importantly, make you fat. So stay
away.
www.thetruthaboutsplenda.com"

Before you pay much attention to what Mr. Trudeau has to say in his
infomertials or books, you might want to check out:

http://www.infomercialwatch.org/tran/trudeau.shtml

and
http://www.quackwatch.org/01QuackeryRelatedTopics/DSH/coral.html

" according to a report in the Wall Street Journal, Trudeau served
nearly two years in prison. In 1990, he pled guilty to larceny in a
Cambridge, Massachusetts, state court in connection with $80,000 in
worthless checks he had deposited at a bank. The sentencing memorandum
said that he had posed as a doctor to increase his credibility with
bank officials. In 1991, he pled guilty to credit-card fraud in Boston
federal district court. Among his misdeeds in the federal case, he
misappropriated for his own use the credit-card numbers of customers
of the memory-improvement courses that he offered at the time ."

There is some good information about Splenda on the site of Dr. Joseph
Mercola, a licensed D.O. who is very active in promoting good health
through nutrition and other natural approaches. His page on Splenda
cites a number of scientific studies and articles with bibliographic
information. Have a look here:
http://www.mercola.com/2000/dec/3/sucralose_dangers.htm#