The study, which was carried out at Creighton University and published last week in Nutrition Today, found that the calcium actually available in some soy and rice drinks can be as much as 85 percent lower than the amount on the product label, owing to the mineral settling at the bottom of the pack.
"The issue comes when they [soy drinks] deliberately go head to head with cow's milk," said Dr Heaney.
This marketing strategy can confuse consumers into thinking that non-dairy options offer the same nutritional benefits as milk.
"Some degree of fortification will produce a better effect than none," he said, and are especially useful for consumers who have an aversion to the taste of milk.
But as consumers become more educated about the benefits that products offer they will hold manufacturers to account.
"Each and every one of the manufacturers of the products tested in the study could have come up with a better formulation," said Heaney.
In a competitive and rapidly growing market, a product's success is determined by more than its efficacy however.
While Minute Maid's Heart Wise orange juice with plant sterols has proved a success, Benecol cholesterol-reducing margarine has struggled. According to Virginia Lee, research analyst at Euromonitor, this may be because we have never seen margarine as a healthy product, so introducing a version with health benefits does not resonate with consumers.
She warns that manufacturers may set themselves up for a fall by loading products with functional ingredients without being fully aware of other factors besides price that will persuade consumers to buy them - that is, taste, and whether the foodstuff itself is seen as inherently healthy.
Euromonitor estimates that the US packaged functional foods market was worth $5.2 billion in 2004, up 8 percent on the previous year. By 2009 it expects it to reach around $6.9 billion, representing 32 percent growth over the next five years.
Recent weeks have seen the launch of a spate of new companies that are eager to establish a presence in the market early on, whether their activities are centered on finished products or ingedients.
Last week saw the introduction of Brand New Brands, a start-up that has attracted $15 million in venture capital from Burrill & Company, Great Spirit Ventures, Unilever Ventures and Prolog Ventures to develop food and beverage products that incorporate health-promoting ingredients.
At the beginning of the year the Muscadine Products Corporation was formed to market free radical-fighting, anti-inflammatory muscadine grape powders to the nutraceuticals industry.
It seems their timing might be spot on. The current rate of product launches is thought to be sustainable for the next few years, largely thanks to the aging population's preoccupation with its health and media coverage of obesity-related issues which encourage Americans to pay more attention to their diet.
"People's fear and guilt will prompt them to eat more fortified and functional foods," said Lee.
However the new Dietary Guidelines for Americans published last month promote a back-to-basics approach to a healthy diet, setting out recommended intake of important food groups such as whole grains, vegetables and omega-3 rich oily fish.
The guidelines make no mention of fortified and functional foods although this does not mean they have no role to play. On the contrary, they could help Americans meet some of the recommendations that are harder to achieve, such as increased consumption of vegetables or oily fish.
"They will turn to functional foods to bridge the gap," Lee predicted.
She also expects that price differences between fortified or functional foods and traditional foods is likely to narrow, and the cost of adding functional ingredients has also gone down too, making it a much more attractive proposition for manufacturers.
As the category continues to evolve and stabilize, the next five years will be crucial in determining whether fortified and functional foods take root, or whether they will be decreed just another passing fad.
At the moment the signs are pointing towards the former, but manufacturers must be circumspect in their launches. Adding functionality to any and every product will dilute the appeal of the really effective products, and make consumers eye all functionality claims with skepticism.