A gluten-free for all drives product sales | Reuters

Truman is among the estimated 18 million people in the United States who are sensitive to gluten -- a hard-to-digest protein found in wheat, rye and barley.

Another 3 million-plus Americans are thought to have celiac disease, a potentially life-threatening autoimmune disorder that is treated by eliminating dietary gluten.

In business, as in acting, good timing proved crucial for Truman.

Sales of gluten-free products have been booming despite the weak U.S. economy. Health advocates and gluten-free celebrities such as 2011 U.S. Open champion Novak Djokovic, Chelsea Clinton and TV host Elisabeth Hasselbeck have helped drive demand by raising awareness about celiac disease and gluten sensitivity.

Truman also had the good luck of being a friend and neighbour to Waylynn Lucas, one of Los Angeles' most celebrated pastry chefs, who is a fan of her gluten-free goodies.

The two now are partners in (fonuts), a new coffee shop that sells baked, not fried, doughnuts. Gluten-free options account for half of sales at (fonuts).

Lucas said customers are either avoiding gluten themselves or "have a friend, a boyfriend, a girlfriend, a cousin, a father, a mother, a whatever, who is gluten intolerant."

"When they see it can be delicious and a little more healthful, they're really turned on," Truman said.

GLUTEN-FREE GROWTH

Gluten is everywhere. It is in baked goods, pasta and beer, as well as some unexpected items, such as McDonald's (MCD.N) French fries, lunch meat, lipstick and some medicines.

Euromonitor International forecasts 2011 gluten-free sales of $1.31 billion in the United States and $2.67 billion worldwide. Sales have more than doubled since 2005 and are expected to hit $1.68 billion in the United States and $3.38 billion globally in 2015.

"Consumers do feel some sort of reward when they eat gluten-free products. They don't feel bloated. They don't have belly aches. This usually encourages them to repeat the purchase," said Ewa Hudson, Euromonitor International's head of health and wellness research.

Europe is ahead of the United States when it comes to celiac disease testing and awareness. Italy, for example, helps people with celiac disease pay for the additional cost of gluten-free foods.

But big U.S. companies are jumping into the fray.

General Mills Inc (GIS.N) is a leader, having reformulated some Chex breakfast cereals, Betty Crocker cake and brownie mixes and Bisquick pancake mix to remove gluten.

Anheuser Busch Inbev SA (ABI.BR) sells a gluten-free beer called Redbridge, which is sold in many mainstream supermarkets.

P.F. Chang's China Bistro Inc (PFCB.O) for years has had a gluten-free menu and Subway, the popular sandwich chain, is testing gluten-free bread and brownies in Texas and Oregon.

Media mogul Oprah Winfrey and actress Gwyneth Paltrow have talked about avoiding gluten as part of detox diets, comments that prompted critics to dub gluten-free the diet du jour.

Trend chasers who have no medical reason to be on a gluten-free diet account for more than half of the daily consumption of gluten-free products, said Alessio Fasano, medical director at the University of Maryland Center for Celiac Research.

Top-notch professional athletes are the only other people who get some measurable benefit from cutting out gluten without a doctor's orders, he said. Eliminating dietary gluten appears to free up energy that otherwise would be used to break down the tough-to-digest protein, said Fasano, who joked that athletes use the diet as a "legal performance enhancer."

Still, he does not mind that fads are boosting sales.

"If anything, it's good for the market" because the extra customers should help improve quality and lower cost, he said.

Interest from big retailers such as Wal-Mart Stores Inc (WMT.N) also should help bring down gluten-free product prices, which run 2 percent to 3 percent higher than similar items containing gluten, said Alice Bast, founder of the National Foundation for Celiac Awareness.

Consumers have been preoccupied with food sensitivity for some time (remember lactose intolerance?) and there is growing interest in foods that support digestive and overall health, said Tamara Barnett, ethnographic research manager at the Hartman Group, a research and consulting firm. Gluten-free products overlap those trends, she said.

Better-tasting products also help.

"They went from being sawdust to being really good," said "Living Gluten-Free for Dummies" author Danna Korn.

Shauna James Ahern was diagnosed with celiac disease in 2005 and recommends focusing on readily available and naturally gluten-free foods such as fruit, vegetables, dairy and meat.

The cookbook author and "Gluten-Free Girl" blogger, says the category has staying power and suspects she knows why people who do not have a medical reason for going gluten-free feel better when they do.

"They're eating whole foods for the first time in their lives," she says.

(Reporting by Lisa Baertlein; editing by Andre Grenon)