In a short-term study of 22 women, researchers found no hunger-quashing effects of chocolate bars containing four different "functional fibers," such as inulin -- aka "chicory root extract" -- commonly found in fiber-enriched processed foods.
Overall, the women were just as hungry come lunch time as they were on a day when they ate a low-fiber bar for breakfast. Their food intake for the rest of the day was similar as well.
The findings, reported in the Journal of the Academy of Nutrition and Dietetics, are in line with other research on added fibers.
"In general, added fibers don't work across the board" when it comes to helping you feel fuller longer, said senior researcher Joanne Slavin, a registered dietitian and professor at the University of Minnesota in St. Paul.
That does not mean to eliminate fiber-enriched foods, though, Slavin said.
"It's hard to get people to eat enough fiber. It's one of our shortfall nutrients," Slavin told Reuters Health. "I think putting fiber into foods that people will actually eat is a good thing."
"It would be nice if these foods had an effect on satiety," Slavin added. On the other hand, she noted, they may still help keep one regular or control cholesterol.
For the study, Slavin's team recruited 22 young women who were not trying to lose weight. They had each woman eat five different chocolate crisp bars on separate days; four of the bars had one of four added fibers, while the fifth one had no extra fiber.
The women had one bar in the evening and then a bar for breakfast the next morning. They then had lunch at the research lab, where they rated their fullness and hunger on a standard scale. After that, they used diaries to record their food intake for the rest of the day.
Overall, Slavin's team found, there were no differences in the women's hunger ratings or food intake with the fiber-rich bars versus the low-fiber one. The fiber did, however, cause more gas and bloating.
The Kellogg Company, which provided the bars used in the study, said the products were developed specifically for the research and are not on the market.
"This study is part of our ongoing efforts as a fiber leader to support research on potential benefits from different fibers to understand how to provide the best nutrition to our consumers," Kellogg spokesperson Kris Charles said in an email.
So which products on the supermarket shelf contain functional fiber?
The easiest way to tell is to look at the amount of fiber, according to Slavin. If a processed food has 9 or 10g of fiber, rather than 2g, it is probably via an added fiber. (The bars in this study each contained 10g.)
One of the fibers tested in this study was inulin, which is commonly used by manufacturers -- in part, because it can add a sweet flavor. On an ingredient list, Slavin said inulin may turn up as "chicory root extract," for example.
Inulin is also what is known as a "fermentable" fiber. It passes undigested into the colon, where it is fermented by bacteria and may stimulate the growth of "good" bacteria. In theory, fermentable fibers could do more to suppress hunger.
However, that did not pan out in this study. Three of the added fibers were fermentable, but they were no more effective in appetite control than the fourth -- resistant wheat starch, which is not fermented in the colon.
It is a common perception that extra fiber fills the consumer up for longer, but according to Slavin, subjective feelings of fullness may go beyond the fiber itself.
In one study, she and her colleagues found that a breakfast of oatmeal and fruit was more satisfying to people than a liquid breakfast with the same fiber content.
Slavin said she thinks it is the total experience of eating fiber-rich foods -- the chewing, the sight of a big bowl of oatmeal -- that makes people feel more satisfied. "You really know you're eating fiber," she said.
With a fiber-added chocolate bar, the experience is different. "With these products, it's like eating a brownie," Slavin said.
Of course, fiber is only one of the nutrients we need. Slavin said that even if someone does choose fiber-added processed foods, they still need to eat fruits, vegetables and other "whole foods" that provide a range of nutrients.
In general, experts recommend limiting processed foods in favor of whole ones.