Concerned about losing the calorie-conscious, smoothie makers are whipping up no-sugar and faux-sugar blends.

That Orange Twister will saddle you with just 140 calories.

Smoothie companies are increasingly focusing much of their marketing muscle on winning over the ultra-health-conscious consumer — especially those trying to eat less sugar.

"There are a lot of folks that aren't hindered by high sugar, but we do know that there's a significant percentage that are, and we think that number's growing all the time," said Jim Baskett, an executive with the Seattle-area chain Emerald City Smoothie.

Many makers are turning to Splenda, the zero-calorie artificial sweetener. Some have drinks that are only fruit and juice. Executives at several smoothie companies say the low-sugar offerings have fared impressively — right alongside popular higher-cal versions.

The smoothie industry has been on an upward climb in recent years, with many chains big and small expanding their reach with new stores.

In 1997, there were just under 1,000 juice and smoothie bars in the U.S., pulling in an estimated $340 million in revenue. Today, there are roughly 5,000 of them, with 2007 sales projected at $2.5 billion, according to Juice Gallery Multimedia, a publishing and consulting firm that provides support services for the businesses.

In the beginning, many customers were health nuts. But the appeal now is much more mainstream and many of the offerings defy a healthy label by calorie count alone.

Take The Blender, a 1,270-calorie whopper made with chocolate or vanilla protein, peanut butter, banana, milk and ice cream, made by Emerald City. And there's Anne Kessler's favorite, the Mocha Bliss, another of the chain's more indulgent offerings.

"It just tastes good," she said, sipping down a tall one recently in her neighborhood smoothie shop.

But for her 2-year-old daughter, Kessler only orders from the low-sugar menu. Usually it's a banana-strawberry-papaya concoction with less than half the calories of her chocolatey choice.

Emerald City, which is gearing up to expand beyond a handful of Western states into Hawaii and New York, is among the Splenda users. So is Jamba Juice, a company based in the San Francisco area that last year also introduced a line with no added sweeteners.

Smoothie King, headquartered in the New Orleans area, sweetens many of its drinks with honey and raw cane sugar. But it allows customers to "Make It Skinny" by skipping the sugar, with a Splenda option.

Freshens Smoothie Company, a unit of Atlanta-based Freshens Quality Brands, offers some Splenda-sweetened drinks and prominently posts on its menu boards that 21-ounce servings of each contain less than 155 calories.

Along with the trend toward Splenda are other new ingredients — unrelated to calorie counts — that smoothie makers are hoping will entice. There's acai (pronounced AH-sigh-ee), a Brazilian berry touted as an antioxidant. There are plant sterols, soy and something called conjugated linoleic acid. Freshens is considering tweaking its yogurt base to add probiotics, a trendy food additive that some claim boost the immune system.

In general, consumer health advocates applaud efforts to make smoothies healthier. But serving sizes remain a frustration for the experts.

"When I was growing up, we had 6-ounce servings of orange juice. ... People don't drink 6 ounces of anything anymore," said Marion Nestle, a nutrition expert and professor at New York University.

The standard size of smoothies in many stores is 24 ounces.

Bonnie Liebman, director of nutrition for the Center for Science in the Public Interest, a health advocacy group, questions why people seem so eager to gulp their fruits in giant single servings rather than eating them whole — an apple here, an orange there.

"The idea is to fill up on fruit and vegetables so you have less room for calorie-dense food," she said.

Smoothie companies say most of their customers use smoothies as meal replacements.