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What are the Microbial Benefits of Cranberries?

The star fruit – or berry – of November is the cranberry. Its luxurious deep pink color brightens the foodscape on the Thanksgiving table and on our plates. Many of us remember Thanksgivings of yore where the cranberry came out of a can in one tubular gel (some of us even remember the sound – “thwoschk!” -- as it ejected from the can and landed on the platter). In recent years, a more wholesome and nutritious cranberry sauce has overtaken the chemical-laden tube.

Whether it be a slice of tubular gel, as a salsa/sauce/chutney, dried for desserts, snacks and salad adds, and as a juice, Vaccinium macrocarpon, the North American cranberry, is a health-promoting powerhouse. Nutritionally, one up of cranberries is only 46 calories (energy units), has 4.6 grams of fiber, 4 grams of sugars (as fructose, glucose and sucrose) and 12.2 grams of carbohydrates. Cranberries also contain vitamins C, E and K1, as well as copper and manganese.

Beyond that, according to a nutritional review, in cranberry, “Flavonoids, especially colored anthocyanins, abundant flavonols, and unique proanthocyanidins, have attracted major research attention. Other notable active components include phenolic acids, benzoates, hydroxycinnamic acids, terpenes and organic acids.”

Consuming foods with whole cranberry has nutritional benefits because of the rich antioxidants found in the skins (not present in the juice or extract). According to research, the antioxidant profile of cranberry is dense and biologically dynamic, containing abundant amounts of quercetin, myricetin, usrolic acid, peonidin and condensed tannins, also called A-type proanthocyanidins.

Thwarting Bad Bacteria

The key superpower that cranberry has – and that research bears out – is it is an enemy of pathogenic bacteria. It acts like Teflon® -- bacteria intent on doing harm just can’t root themselves to start their mayhem. The two primary enemies that cranberry valiantly fights are Escherichia coli and Helicobacter pylori.

The most common health byproduct associated with consuming cranberry is curtailment of urinary tract infections. Millions of women turn to cranberry juice or supplements when the first sign of flareup begins – nearly one and three women will have at least one UTI by age 24 and are “significantly more likely” to endure a UTI than men. UTI is caused by the bacterium E. coli.

Cranberry is distinctive among other proanthocyanidin-containing foods such as grape and apple juices, green tea and dark chocolate as it contains A-linked proanthocyanidins, while the others have B-linked proanthocyanidins. The differences between the two types were put to the test, meaning which one prevented E. coli adhesion better? The researchers found that “the isolated A-type proanthocyanidins from cranberry juice cocktail elicited in vitro anti-adhesion activity at 60 microg/ml, the B-type proanthocyanidins from grape exhibited minor activity at 1200 microg/ml, while other B-type proanthocyanidins [green tea, dark chocolate] were not active. Results suggest that presence of the A-type linkage in cranberry proanthocyanidins may enhance both in vitro and urinary bacterial anti-adhesion activities and aid in maintaining urinary tract health.”

Another study of a powdered cranberry standardized to proanthocyanidin content showed that just 72 mg of proanthocyanidins daily can protect the urinary tract lining from E. coli adhesion.

In a randomized study, 137 women with two or more antibiotic-treated UTIs in the previous 12 months were randomized to receive either 500 mg of cranberry extract or 100 mg of trimethoprim (a common prescription for UTIs) for 6 months. After a year, 39 of 137 participants (28%) experienced a UTI (25 in the cranberry group and 14 in the trimethoprim group). “Trimethoprim had a very limited advantage over cranberry extract in the prevention of recurrent UTIs in older women and had more adverse effects,” the study team concluded.

Several meta-analyses seem to confirm this benefit of cranberry. One review of 10 studies with 1049 participants concluded that here is some evidence that cranberry juice may decrease the number of symptomatic UTIs over 12 months, particularly for women with recurrent UTIs. This was also the findings of another review of 13 trials with 1,616 participants. A third meta-analysis of 17 studies with 2,165 participants found that, along with prescriptions such as the vaginal vaccine Urovac®, cranberry consumption also decreased the recurrence rate of UTIs. 

Meanwhile, another barbaric bug, Helicobacter pylori, when left unaddressed, can wreak havoc with well-being, especially in the digestive system, where it causes ulcers. “Cranberry constituents are known to exert anti-adhesion activity on H. pylori in vitro,” write authors of one study investigating the actions of cranberry juice on H. pylori in people taking prescriptions. In this study of177 adults with H. pylori found that both men and women experienced more eradication of the bacteria from cranberry/antibiotic combination than in the antibiotic-only group.

One study focused on how cranberry juice impacted the presence of H. pylori utilizing a test called 123C-urea. The randomized, double-blind, placebo-controlled trial – 189 adults with positive 123C-urea breath tests found that after 35 days,14 of the 97 subjects in the cranberry juice treatment group yielded negative test results versus 5 of the 92 in the placebo group.

Promoting Good Bacteria

In a study, researchers point out, “Probiotics and cranberry have been shown to inhibit Helicobacter pylori owing to bacteriocin production and high levels of proanthocyanidins, respectively. These effects have been confirmed in clinical trials with H. pylori-positive subjects. They found that both cranberry juice and the probiotic strain individually were able to inhibit H. pylori from colonizing.

Cranberries are also a type of prebiotic: xyloglucans are found within the cell walls of cranberry, and they have been found to feed bifidobacteria. In another study, xyloglucan fractions in cranberry juice were found to specifically hinder the adhesion of E. coli CFT073 and UTI89 strains to bladder epithelial cells and that of E. coli O157:H7 to colonic epithelial cells. The authors write that the xyloglucans “represent a new cranberry bioactive component with E. coli anti-adhesion activity.”

Researchers in another study emphasized that xyloglucans are not digested before they reach the colon which is important because here, the xyloglucans interact with bifidobacterial to promote health. They explained, “Specific bacterial strains utilize cranberry xyloglucans as a nutritive source, indicating unknown mechanisms that are not universal in bifidobacteria….we observed cross-feeding between bacteria in which one strain degrades the cranberry xyloglucan to make it available to a second strain. Similar nutritive strategies are known to occur within the gut. In aggregate, this study may lead to novel foods or supplements used to impact human health through rational manipulation of the human microbiome.”


Whole cranberries are prominently available in supermarkets this time of year and can be purchased all year long. You can certainly go with the traditional cranberry jelly (make a smoothie bowl with it) or try something new, fun and tasty with whole cranberries (especially for the microbial benefits). For example, a Google search of “cranberry recipes” yields approximately 154,000,000 results. So, you can enjoy not only the taste of this berry but also its benefits in many ways all year long!

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