Foods such as yogurts supplemented with fiberlike sugars are developing into the latest wave in functional foods–commercial goods seeded with ingredients that boost their nutritiousness or healthfulness. Makers of foods doctored with these unusual, nearly flavorless sugars claim that their products improve the body’s absorption of calcium in the diet, thereby offering bones a treat.

CALCIUM HELPER? Dairy products, such as yogurt, can be supplemented with odd sugars called nondigestible oligosaccharides. Their large fiberlike molecules seem to enhance the body’s absorption of bone-building calcium.

Just hype? Apparently not, according to a series of experiments in animals and people. A report of the most recent animal tests, conducted by researchers at Purdue University, appears in this month’s Journal of Nutrition. It suggests that by judiciously supplementing the diet with these carbohydrates, an elderly woman might significantly reduce her risk of osteoporosis.

Connie M. Weaver and her colleagues laced the food of female rats with materials that are known commercially as nondigestible oligosaccharides. Her group had removed the rodents’ ovaries to simulate the hormonal environment typical of postmenopausal women. The drop in circulating estrogen after menopause can promote bone loss.

After just 2 weeks on a diet enriched with these sugars–a mix of inulin and fructooligosaccharides–the animals’ bones were notably bigger and richer in calcium than those of rats without ovaries raised on normal, unsupplemented feed.

But these are rats; what about people? Weaver notes that a recent study in adolescents reported improved calcium availability when the test volunteers supplemented their diets with about 9 grams per day of these unusual carbohydrates. The Purdue team now plans to investigate whether elderly women would show benefits from a similarly modest supplementation.

Not your average sugars

Weaver points out that the oligosaccharides her team is using, although they’re sugars, “aren’t the sugars you’re used to seeing on the table.” Oligosaccharide molecules are bigger–so big that they “fall into the category of dietary fibers” and are resistant to degradation, she notes.

Orafti Active Food Ingredients is a Belgium-based supplier of these compounds to food manufacturers. Explains Orafti’s Kathy R. Niness, these atypical carbohydrates are linked molecules of the simple sugar fructose. She notes that the particular bonds linking the fructose units “render them nondigestible by human intestinal enzymes.” As such, these large molecules pass through the mouth, stomach, and small intestine without releasing their calories–which helps keep blood-sugar concentrations low.

Some calories are released further down in the gut, so these oligosaccharides aren’t caloriefree. At a conference sponsored by the National Institutes of Health a few years ago, Marcel B. Roberfroid of the Catholic University of Louvain in Belgium reported that in contrast to fructose, which delivers about 4 calories per gram, oligofructose and inulin each release only about 1.5 calories per gram.

At that meeting, Niness noted that numerous studies have shown that consumption of these sugars has “no influence on [blood sugar and] no stimulation of insulin.” For just that reason, “inulin has a long history of use by diabetics,” she says.

However, Weaver notes, bone benefits stem from the oligosaccharides’ other benefits. Several studies have suggested that oligosaccharides promote calcium absorption in the gut. Curious as to how these carbs might do that, Weaver designed her new study to evaluate what happens to the calcium content of bone in animals eating oligosaccharides.

Bone is constantly forming and breaking down. Ideally, those processes should balance each other or perhaps favor bone production. In rats, the oligosaccharides-supplemented food slowed the rate of bone breakdown and slightly increased the rate of bone formation.

Intestinal microbes in the lower gut can break down these carbs. And in doing so, Weaver notes, “they increase the acidity there.” That’s a good thing, she adds, “because calcium is more soluble in acid” and therefore more of it comes out of food and is available to move from the gut into the bloodstream.

Indeed, her group’s data indicate that to affect calcium absorption, these supercharging carbs must be in the gut at the same time calcium-bearing food is passing through. When the oligosaccharides and food were delivered at different times of the day, rats absorbed no more calcium than did animals not receiving the oligosaccharides.

Bigger bones

In Weaver’s new study, the oligosaccharide additives increased the rats’ absorption of calcium from food by 85 percent. More importantly was the demonstration that the supplemented food benefited bones. After just 2 weeks, the calcium content of certain leg bones increased an average of 7 percent over those in animals eating chow that didn’t contain the unusual sugars.

These changes are enormous, says Weaver, even though the amount of oligosaccharides given to the animals wasn’t. In fact, she says her data suggest that the average person might see bone benefits by adding just a couple teaspoons of oligosaccharides to his or her daily diet.

Although these unusual carbs are usually derived from chicory–the root of Belgium endive (Cichorium intybus) plants–they appear naturally in thousands of plants. When commercially purified, they’re only a trifle sweet, Weaver notes, so a powdered form could easily be mixed into a glass of milk, yogurt, or some other calcium-rich food. Indeed, the Londonderry, N.H.–based dairy Stonyfield Farm already adds inulin to some yogurts, such as its organic product called Moo-la-la (

Weaver notes that interest in inulin and fructooligosaccharides is already high in Europe, where intestinal health is a keen selling point for consumer products. Because that’s pretty much a nonissue in the United States, she says, bone health will likely prove a more effective marketing claim.

But there are even more potential benefits to these unusual carbs–both for people and pets–as research slated to be presented next week at a Paris conference suggests. One meeting session will focus on the role of these agents as mood-brightening food additives. Another will show how they might benefit people with ulcerative colitis and risk of colon cancer. Still other reports will focus on the ability of oligosaccharides to boost immunity.

Roberfroid, who will chair the conference, argues that the potential health benefits of these all-natural food additives run the gamut–from controlling intestinal infections and constipation to controlling blood sugar in type 2 diabetes and reducing obesity. Potentially, he says, oligosaccharides offer a little something for everyone.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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