Sales of soy based food and drink products were at 17 percent in 2001-2002, but this rate had decreased to 6 percent in the following 12 months, said Mintel.
The research also showed a decline in usage with 27 percent of consumers reporting using soy products in 2004 compared to 30 percent in 2002.
Most grain-based products could be seen as a rival to soy, but "none of the significant ones has as fast a growth rate as soy", Mintel analyst David Lockwood told FoodNavigatorUSA.com.
Moreover, he admitted that it is normal for growth of any product to slow down after an initial burst, particularly when the sales growth is at such a high rate. And, the growth of soy sales "is still about double that of overall grocery store sales".
Indeed, 435 products with soy as a key ingredient were launched in 2004, up from 329 in 2003.
The fastest growing categories lasy year were sauces and seasonings - "also the leading category in terms of the number of rollouts" - and bakery.
Dairy applications, on the other hand, have been steady for the past three years, "showing that the amount of innovation there is at a plateau," said Lockwood.
Soy products can be found in a host of segments from frozen desserts, salad dressings, and snacks and according to Lockwood, the technology for putting soy in food and beverages is just "entering a middle stage", meaning there is still much more that can be done with the ingredient.
Strong sales growth since 1997 has been helped by a steady stream of studies that suggest the benefits of soy, but they are are a long way from being understood by the general public.
A survey in 2002 showed that only 29 percent of consumers said they knew that the FDA endorsed soy as heart-healthy - compared to 86 percent for calcium and bone health and 56 percent for oats and heart health.
At the other end of the scale, certain negative reports concerning soy could have had an effect on sales.
"The rush to try soy as a replacement for estrogen therapy during menopause has decreased since it has become clear that this usage might not be as effective as hoped," said Lockwood.