Survey numbers differ, making it difficult to decide whether gluten-free is niche or mainstream.

Hardly anyone would argue the gluten-free market is big and growing, but just how big may depend on the source cited. Numbers differ by survey, making it difficult for food companies to decide whether to position a gluten-free product for the mainstream market or for a niche market.

Mintel, a Chicago-based market research company, late last year said it expected the U.S. gluten-free market would reach $8.8 billion in 2014, marking a 63% jump from 2013. Leading categories for gluten-free sales were snacks at $2.8 billion, meats/meat alternatives at $1.6 billion, and bread products and cereal at $1.3 billion, according to the company.

Packaged Facts, another market research firm based in Rockville, Md., also reported growth, but a smaller overall sales number, in a survey taken in July and August of 2014. Retail sales of gluten-free foods in the United States reached $973 million after posting a compound annual growth rate of 34% over a five-year period, according to Packaged Facts, which projects U.S. gluten-free sales will exceed $2 billion in 2019.

Elizabeth Sloan, Ph.D., president of Sloan Trends, Inc., Escondido, Calif., said she has seen outlets reporting the global gluten-free market as high as $23 billion, a figure she looks at with skepticism. She said products inherently gluten-free may add to gluten-free sales estimates. For example, when bottled water passes across the scanner at a retail outlet, it may pad gluten-free sales figures.

“There is no intent to buy (gluten-free) when you scan it,” Dr. Sloan said during a July 13 presentation at the Institute of Food Technologists’ annual meeting and food exposition in Chicago. “You could buy it for a totally different reason, and it says gluten-free on the back. These are niche markets.”

She pointed to data from Ardent Mills, Denver, as perhaps being a better indicator of the gluten-free market. Ardent Mills defines gluten-free products as specialty items that are directed intentionally to consumers who need or want to buy a substitute for products with wheat, barley or rye. Ardent Mills eliminates three types of products: those that inherently are gluten-free such as corn meal, products that do not carry obvious gluten-free package claims, and products that were sold by diversified companies that were not targeting the gluten-free community with the product.

Research from Ardent Mills shows U.S. gluten-free sales reached $1.2 billion in 2013, up 47% from 2012. Average annual sales of gluten-free specialty products grew 40% from 2009 to 2012, or to $831.8 million from $320.4 million, according to the company.

Other surveys have tried to shed light on the gluten-free market as well. The International Food Information Council Foundation’s Food and Health Survey 2015 found 19% of respondents said they were trying to limit or avoid gluten entirely, which was up from 13% in 2014.

Dr. Sloan in her I.F.T. presentation pointed to a 2015 study on U.S. grocery shopper trends from the Food Marketing Institute, Arlington, Va. It showed 10% of shoppers sought gluten-free claims in 2015, which was down from 11% in 2014.

Dr. Sloan also referred to a 2013 Gallup study on “clean labels” for foods and beverages. When asked what label terms or descriptions would “greatly increase” their purchase intent, 20% of the people aged 18-34 and 20% of the people aged 35-49 said gluten-free. The gluten-free percentages were 14% for people aged 50-64 and 12% for people aged 65 and over.

A June 4 webinar put on by the Natural Marketing Institute, Harleysville, Pa., showed many people choose gluten-free products for perceived health benefits. When the N.M.I. asked people to give their reasons for eating gluten-free items, 51% said for improved overall health, 38% said to feel better and 27% said to lose weight. Only 6% said because they had celiac disease, which means medically they must avoid gluten in their diet.

Food companies, when choosing how much to invest in gluten-free products, also may take into account whether a large number of consumers will continue to consider the products as healthy.

At least one study has cast doubt on the health aspect. Researchers from the University of Sydney in Australia evaluated products from supermarkets in Sydney in 2013. They studied the nutrition information panels of 3,213 total food products across 10 categories and gave them a “health star rating” ranging from 0 (the worst) to 5 (the best). Gluten-free plain dry pasta scored nearly a 0.5 point star less than regular pasta. There were no significant differences in health star ratings for bread or ready-to-eat breakfast cereal. Gluten-free products consistently had lower average protein content across the three categories of pasta, bread and R.-T.-E. cereal.

Results of the study appeared on-line June 29 of this year in the British Journal of Nutrition.