The holiday table would look dull, lifeless, and naked without an intensely colorful, jellied, saucy, free-form, or cylindrical cranberry side dish. We believe in the festive and medicinal properties of these sour little berries, so let’s take a closer look and see whether they are truly the crimson crusaders of our dreams.
Why aren’t cranberries sweet?
Berries begin their lives tart, to discourage animals from eating them before their seeds are mature. Then, when the time is right, most berries become sweet to entice hungry animals to munch upon them, but not so the cranberry. I was fascinated to learn that cranberry bushes do not use animals to spread their seeds; they use water! Cranberries are very light and contain inner air pockets. When cranberry bogs flood, or if the ripe buoyant berries fall off the cranberry bush, they simply float away with the current in hopes of being deposited on a distant bank. They don’t need animals to help them reproduce, so they don’t need to go to the trouble of sweetening their fruits. Nature is amazing.
Since we’re not designated by the cranberry plant as preferred seed carriers, clearly we are not “meant” to eat cranberries. However, that doesn’t necessarily mean that they are bad for us. In fact, there are many studies which suggest they may be good for us under certain conditions, most famously in the case of urinary tract infections, or UTIs. Is that true? If so, what is their secret ingredient?
Cranberry ingredient list
Cranberries contain numerous chemicals with interesting properties: proanthocyanidins, triterpenoids, lectins, catechins, ascorbic acid, benzoic acid, quinic acid, oxalic acid, citric acid and malic acid. Of these, the ones that have been the most intensely studied are the “proanthocyanidins”, or PAs for short. PAs are also commonly referred to as tannins, and it is the presence of these chemicals that gives cranberries their astringency (they make your mouth feel dry). PAs belong to the polyphenol (aka flavonoid) family of plant compounds. Plants use these bitter chemicals to ward off hungry creatures such as bacteria and insects, and to protect themselves from harsh weather. Plants can also break PAs down into a rainbow of colorful pigments. PAs can be grouped into two major categories, depending on their chemical structure: A-type and B-type. B-types are found in a wide variety of foods, including red wine (grape skins), coffee, tea and chocolate. A-type PAs are uncommon, being found only in cinnamon, plum, peanut, and our friend, the cranberry.
A-type PAs are special in that they can prevent many types of bacteria, including E. coli (the most common bacteria found in UTIs), from attaching to certain surfaces, including the cell surfaces lining the urinary tract. Aha.
How might cranberries fight urinary tract infections?
There have been numerous clinical human studies of cranberry juices and cranberry extracts in the prevention of UTIs in all kinds of patients—children, adults, pregnant women, seniors, and people with bladder conditions that require the use of catheters. These studies have varied too much in the types of cranberry products tested and the doses of active ingredients used, and have generated very mixed results. A Cochrane review conducted in 2008 [Jepson et al] concluded:
“Given the large number of dropouts/withdrawals from studies (mainly attributed to the acceptability of consuming cranberry products particularly juice, over long periods), and the evidence that the benefit for preventing UTI is small, cranberry juice cannot currently be recommended for the prevention of UTIs. Other preparations (such as powders) need to be quantified using standardised methods to ensure the potency, and contain enough of the ‘active’ ingredient, before being evaluated in clinical studies or recommended for use.”
A review of randomized controlled trials [Wang 2012] noted the following trends, but they were not strong enough to be statistically significant:
- Cranberry juice is more effective than tablets or capsules of cranberry extract
- Cranberry products work best if taken at least every 8 hours
- Women and children are the most likely to benefit from cranberry treatments.
Cranberry juice treatments are hard to stomach, with up to 50% of subjects dropping out of studies due to side effects (nausea, vomiting, diarrhea, unpleasant taste).
Prevention or cure?
Cranberry PAs have the power to prevent bacterial attachment, but they probably do not have the ability to dislodge bacteria once they have set up shop, therefore cranberry juice cannot be recommended for treatment of existing UTIs. The weak/mixed evidence suggesting that they may help to prevent UTIs in susceptible individuals indicates that one would need to drink cranberry juice 3 times a day every day to reduce risk of future UTIs. It is not yet known what dose of PAs or what volume of cranberry juice may work best, if PAs even work at all…
Is it all just juicy gossip?
It could be that we simply need more robust studies to prove the might of our sour little Cape Crusader. But there may be other factors at play.
We know that cranberries are high in PAs, and that they survive cooking and digestion, but the vast majority of cranberry PAs are not absorbed into the bloodstream and therefore do not make it to the urethra (urinary tract). On average, less than 1% of cranberry juice PAs show up in the urine. Is that a high enough concentration to ward off bacteria? We don’t know. If it isn’t, it could be that the PAs are NOT the secret ingredient in cranberries after all. The fact that cranberry juice seems more effective than cranberry capsules suggests that an ingredient present in the juice that is not present in raw cranberries might be playing a role behind the scenes.
If it’s not the PAs, what is it?
What else is in cranberry juice?
Fructose itself can prevent E. coli from attaching to cells. The vast majority of cranberry juice drinks available are sweetened with corn syrup and/or sugar, both of which contain about 50% fructose (fruit sugar). How much of the power of cranberry juice might be due to the fructose content? We don’t know. However, a large study showed that a low-calorie cranberry juice sweetened with sucralose (Splenda®) did not reduce UTI risk any more than a cranberry-free beverage did [Barbosa-Cesnik 2011]. The authors don’t specify whether the control beverage was also sweetened with sucralose, but I assume that it was. The authors note that the rate of UTI was about 50% lower than expected in BOTH groups, suggesting that both beverages were equally effective. The authors wondered if perhaps it was the vitamin C content in both drinks that was responsible for the possible reduction in UTIs.
Bottom line about cranberries
- The jury is out as to whether cranberry juice is effective in the prevention of UTIs.
- It remains unclear which ingredient(s) in cranberry juice may be helpful in preventing UTIs.
- The tannins / proanthocyanidins within cranberries, which are there for the protection of the fruit in the wilderness, have so far been shown to be non-toxic, probably because they are very poorly absorbed. However, tannins are known “anti-nutrients”, and can interfere with the absorption of dietary iron and protein, for example. For more information about tannins, please see my fruits page.
- The risk of drinking traditionally sweetened cranberry juice 3 times a day, which is very high in sugar and can therefore increase risk of obesity, diabetes, heart disease, and other chronic health problems, probably outweighs any potential reduction in UTI risk.
- Oh, and most importantly, cranberries are cool cuz they float:)
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