Blueberries may reduce the growth of breast cancer! Apples and pears reduce the chance of stroke! I bet I have your attention now. But those are not my words, they’re recent newspaper headlines. It seems that virtually every day some new study comes out touting the ability of this or that food to extend our earthly existence. Usually the researchers themselves are modest in their claims and end their discussion with the inevitable call for more research. But then the media get a sniff of the action. And in the drive to capture public attention, science sometimes takes a back seat. Before long, a smidgen of science may be blended with a dash of hope and a healthy dose of hype to cook up a scrumptious headline. But for the scientifically-minded, the tasty headline may trigger a bout of mental indigestion.
The blueberry story is a report of an interesting study carried out on female nude mice. Don’t get any mental images of Minnie enticing Mickey, these nude mice are specially bred for laboratory research. They derive from a strain with a genetic mutation that causes them to have an underactive thymus gland resulting in an impaired immune system. Outwardly they lack body hair, hence the nickname “nude”. Suffice it to say that these nude mice are not a perfect model for predicting biological effects even in other mice, never mind in humans. Still, they are valuable in research because cancer cells can be introduced without a rejection response. And the blueberry study was all about mice being injected with breast cancer cells. But these were very specific breast cancer cells, known as “triple negative cells.”
The “triple negative” refers to the fact the growth of these cells is not supported by the hormones estrogen or progesterone and that they also test negative for the presence of “human epidermal growth factor receptor 2 (HER2),” a protein that promotes the growth of cancer cells. “Triple negative cells” therefore do not respond to standard hormone blocking drugs such as tamoxifen or to medications like herceptin that interfere with the HER2 receptor. Triple negative cells are very aggressive, but are the cause of only 15% of all breast cancers.
Now back to our blueberries. Researchers at City of Hope Hospital in Los Angeles treated nude mice to a diet that included either 5% or 10% blueberry powder by weight. After two weeks, the mice were injected with the triple negative breast cancer cells. A control group of animals was fed in the same fashion but without the blueberry powder.
Why undertake such an experiment? Because earlier laboratory studies had shown that blueberry extract had “anti-angiogenesis” activity, meaning that it interfered with the formation of blood vessels that tumours need to grow. After six weeks, the mice fed the 5% blueberry diet had a tumour volume that was 75% lower than the control animals, but strangely, those fed the higher dose blueberry diet showed only a 60% lower tumour volume. In terms of human equivalents, the 5% blueberry diet corresponds roughly to eating about two cups of fresh blueberries a day. In a second study, the blueberry-fed mice exhibited a reduced risk of the cancer spreading to other parts of their body.
What then would be a realistic headline to describe these results? How about, “Large daily dose of blueberry powder may reduce the growth of a rare type of artificially induced breast cancer in a special variety of immune suppressed mouse?” Wouldn’t sell many papers, one would guess. And what do these mouse experiments mean for humans in terms of preventing or treating breast cancer? Not much. All we can do is mutter that blueberry extracts “warrant further investigation.”
Marketers of course are not tethered to science. Any blueberry study that hints of some positive outcome, no matter how irrelevant it may be to humans, is enough to trigger an outbust of processed foods that feature blueberries on the packaging. You might think, for example, that “Total,” a cereal that loudly proclaims “blueberry” on the box, might actually contain blueberries. Well, you would be wrong. The “blueberries” inside are artificially coloured and flavoured bits of sugar mixed with fat. Even bagels or muffins that actually do have some blueberries contain insignificant amounts for any biological effect. Pure marketing hype.
How about the apple and pear study? Well, it really isn’t a study about apples or pears. Researchers at Wageningen University in the Netherlands analyzed food frequency questionnaires filled out by some 20,000 people in terms of their fruit and vegetable consumption. Based upon the color of their “fleshy” portions, the fruits and vegetables were divided into green, orange and yellow, red and purple, and white.
The subjects were followed for ten years, a period during which 233 suffered a stroke. It turns out that stroke victims were more likely to have consumed fewer “white” fruits and vegetables than the other subjects. The researchers calculated that for every 25 gram increase in “white” fruit and vegetable consumption each day, the risk of stroke decreased by 9%. This may sound like a significant drop but really it is a small effect. Out of some 20,000 people, 233 suffered a stroke. That’s roughly a 1.2% risk. A drop of 9% would mean the risk goes down to 1.1%. In other words, a thousand people would have to increase their “white” intake by 25 grams to save one stroke.
So what are “white” fruits and veggies? Bananas, cauliflower, chicory, cucumber, pears and apples. Within the “white” group, apples and pears were most commonly consumed, hence the catchy headline about apples and pears reducing the risk of strokes.
Now for a splash of critical thinking. First, food frequency questionnaires are notoriously unreliable. People have a hard time remembering what and how much they have eaten. And chances are that dietary habits change over the years. There is no guarantee that the pattern revealed by the questionnaire was followed over the ten year follow-up period. Next, only white fruit and vegetable consumption was linked to a reduced incidence of stroke, not specifically apple or pear intake. Maybe the effect, if indeed there is one, is due to bananas or cauliflower.
This may sound like we’re splitting fruits here. But there is a point. Some reports referred to the 9% decrease in strokes for every 25 grams of “white” fruits and vegetables and suggested that eating an apple a day (roughly 120 grams) can reduce the risk of a stroke by some 45%. That some overly exuberant data dredging. Akin to inferring that blueberries can reduce the risk of breast cancer based on some mouse experiment.
While both the blueberry and apple studies are pretty hollow, they are at least in step with the plethora of publications that attest to the benefits of eating fruits and vegetables. So by all means fill up on blue, white, and whatever other coloured fruits and vegetables you can find. But don’t swallow the next headline about some “superfood” saving you from the clutches of the grim reaper.