Jack in the Box debuted Real Fruit Smoothies in three varieties in April.

And although smoothies once were the provision of health-foods-focused operations on one end or ice-cream parlors on the other, now players as diverse—and as large—as San Diego-based Jack in the Box and Seattle-based Starbucks are moving into the smoothie sector.

Consumers seem to be getting the message. The U.S. smoothie market reached $2 billion in 2006, representing an 80% jump over the previous five years, according to Chicago-based market-research firm Mintel. Generation X—currently a generation of active young professionals and parents of young children—seems particularly enthusiastic. In R&I’s 2008 New American Diner Study, 27.1% of Gen Xers (ages 27 to 41) said they usually opt for a smoothie when buying a snack from a restaurant. Gen Y’s (age 26 or younger) smoothie-selecting population totals an also-healthy 21.8%. By comparison, 26.0% of Gen X members and 16.4% of Gen Y members said they usually choose coffee or coffee-based drinks.

This isn’t to say that smoothies have been an unqualified success. All smoothie-serving operators, but especially those who built their brand around the product, face challenges in terms of consumer perceptions of smoothies’ value. As with coffee drinks, smoothies represent an expense that is relatively easily eliminated for the large number of consumers watching their spending more closely than they did two years ago.

And smoothies don’t have what Steve Kuhnau, co-founder and CEO of Covington, La.-based Smoothie King (and aforementioned allergies and hypoglycemia sufferer), calls “the chew factor.” In considering a smoothie as a snack or a replacement for breakfast or lunch, many consumers wonder whether an item sipped through a straw will be able to satiate them until their next meal.

Operators sell smoothies as a nutrient-packed energy boost in a cup.

The goal of the smoothie experience at each operation dictates the message delivered to customers. At Maui Wowi Hawaiian Coffees & Smoothies, where the tag line is “Where it’s always 72 degrees and sunny,” the emphasis is on a refreshing, taste-of-the-islands treat. “We’ve always marketed ourselves as a fun product that is healthy, not a healthy product that is fun,” says Michael Haith, CEO of the Greenwood Village, Colo.-based chain, which made its Top 400 debut this year at No. 385.

Smoothie King, on the other hand, aims to reap increasing rewards from its “healthful meal replacement” positioning. “People who are into smoothies and are into nutrition, they know the difference,” says Richard Leveille, Smoothie King’s executive vice president of development and real estate.

Promoting the smoothie as a functional meal replacement rather than merely a sweet midafternoon snack or an accompaniment to a sandwich conveys, from a product-development perspective, a focus on health and wellness, say Leveille and CEO Kuhnau. “We put the smoothie right on the center of the plate, where they put it off the plate,” Leveille says.

Adds Kim Larson, director of brand experience at Emeryville, Calif.-based Jamba Juice: “We’ve seen a real significant shift in our business from a lot of our classic smoothies to either All-Fruit or Blended with a Purpose smoothies.”

Operators looking to capture consumers’ growing interest in wellness are focusing on function—on the smoothie that can be tailored to individuals’ goals and needs.

Atlanta-based Planet Smoothie’s “A Smoothie for Every Lifestyle” campaign touts the chain’s five distinct smoothie lines: Energy Smoothies, Weight Loss Smoothies, Multi Vitamin Smoothies, Cool Blended Smoothies and Protein Smoothies. In May, Scottsdale, Ariz.-based Cold Stone Creamery introduced NrGize Smoothies, which can be blended with Anti-Stress, Energy, Protein or Antioxidant supplements.

The health angle is an ideal one to pursue, operators say. “I think the natural progression for us is to be a healthier and healthier alternative to fast food,” says Brad Williford, director of operations for Planet Smoothie. “There’s tons of opportunity and tons of potential for us.”

Ice-cream chains and other operators known for indulgent treats also are testing (or further exploring) smoothies’ potential. Atlanta-based MaggieMoo’s Ice Cream & Treatery sells its new Zoomers Fresh Smoothies as a supersnack with the tag line “Refresh. Refuel. Re-Zoom Your Day.” The Zoomers are available in six varieties, including two made with still-trendy pomegranate and two boasting the caffeine boost of coffee.

“I think it provides more of an in-between-meal snack option as well as a more-refreshing type of dessert,” Jack in the Box Division Vice President for Marketing and Promotions Tammy Bailey says of the chain’s new Real Fruit Smoothies. “It behooved us to open our menu up to things that [consumers] were already choosing at other sites.”