WEDNESDAY, June 8, 2005 (HealthDay News) -- Dentists frequently advise patients to limit their consumption of raisins because this sweet, sticky treat is believed to promote dental decay.
But a study being presented Wednesday at the American Society for Microbiology's annual meeting in Atlanta found that raisins contain compounds that fight bacteria that cause cavities and gum disease.
The implication is that eating raisins may not be so detrimental to dental health after all.
"We're not saying that it's going to prevent cavities," cautioned study author Christine D. Wu, a professor and associate dean for research at the University of Illinois at Chicago College of Dentistry. "But we want to emphasize that raisins are not all bad for you."
Wu's study, funded by the California Raisin Marketing Board, found that raisins are particularly high in a plant-based compound called oleanolic acid, which inhibited two species of cavity- and plaque-causing bacteria in lab analyses that her team performed.
But oral health experts don't expect dentists to start handing out packets of raisins to their patients anytime soon.
"Raisins (due to their high sugar concentration) are among the most cavity-promoting foods we have ever encountered," asserted William H. Bowen, a professor of dentistry, microbiology & immunology and environmental medicine at the University of Rochester School of Medicine & Dentistry.
"So no matter what beneficial agents are in there, they're obviously not sufficient to overcome the harmful effects of the raisins to promoting cavities," he added.
Bruce J. Paster, senior staff member and professor in the department of oral and developmental biology at The Forsyth Institute at Harvard University's School of Dental Medicine, urged caution in interpreting the findings. "Although the results are promising," he said, "you would need a study to show that eating raisins reduced cavities and/or gum disease."
Tooth decay occurs when foods containing sugars and starches are frequently left on the teeth, according to the American Dental Association. Bacteria in the mouth feed on these substances, producing acid that can destroy tooth enamel. Plaque is the sticky film of bacteria on teeth that can cause the enamel to break down and cause cavities unless it is removed by regular brushing and flossing.
Using chemical analyses, Wu and her colleagues found raisins may not be the dental demons they're made out to be. The team identified five specific compounds in Thompson seedless raisins that are known "phytochemicals," or plant-based substances that protect against human disease.
One of the most powerful is oleanolic acid. At a concentration of 31 micrograms per milliliter, this substance prevented the bacteria Streptococcus mutans, a major cause of cavities, from adhering to tooth surfaces. At 62 micrograms per milliliter, it inhibited growth of Porphyromonas gingivalis, a leading cause of periodontal disease, the study found.
It's not clear how many raisins people would need to eat to achieve a similar antibacterial effect, Wu acknowledged.
"In order to test and see if the compounds fight cavities or gum disease, you have to do it in humans," she said. "What we do is we look at its ability to fight the bacteria in the laboratory test -- in the test tube -- and see if they affect the bacteria that are associated with gum disease or cavities."
Still, giving kids, say, gummy bears or chocolate chip cookies, which contain sucrose, or table sugar, is "much worse" than offering them raisins as a snack, Wu insisted. The sweetness of raisins comes from fructose and glucose, not table sugar -- the type that's bad for teeth, she said.
In an earlier study, Wu and her colleagues found no statistically detectable difference between the acid produced in the dental plaque of children who ate plain bran cereal versus those who ate bran cereal plus raisins. However, acid levels spiked when participants ate a commercial raisin bran cereal with added sugar. It isn't the raisins that cause acid production in plaque, Wu explained, it's the sucrose.
Bowen, for one, remains dubious of claims that raisins are a healthful treat. While it may be possible to extract beneficial agents from raisins, as a snack food they are still "one of the worst agents in promoting tooth decay," he said. "No question of it."
The American Dental Association has tips for cleaning your teeth and gums.