Americans have long had a love affair with size. In the supermarket we reach instinctively for plump, perfectly formed produce. Now science suggests it's time to downsize the fruits and vegetables we select for the table while expanding our view of nutrition.
Left to itself, nature copes with drought and other adversities by limiting the size of fruits and vegetables. And that turns out to be good—for us as well as the plants. Compact size concentrates the flavonoid phytochemicals that have significant benefits to human health, such as the deeply pigmented anthocyanins in red grapes and pomegranates.
These bioactive compounds, along with the carotenoids in orange veggies, lycopene in tomatoes, and flavonoids in dark chocolate and green tea, are all so-called secondary phytochemicals—produced by plants as a means to cope with stress. They are not nutrients per se, but they serve important signaling and protective functions in plants—and for our bodies as well.
Flavonoid compounds deliver a triple punch even in small doses. As antioxidants, they scavenge the body for free radicals and neutralize their capacity for cellular damage. They also act as anti-inflammatory agents to combat the stresses of aging and improve cardiovascular and brain function. And they are proving adept at halting cancer.
Plant scientist Mary Ann Lila of the University of Illinois focuses on the phytochemicals and other bioactive compounds in berries, which, she contends, are in a class by themselves. She and neuroscientist James A. Joseph at the USDA's Human Nutrition Research Center on Aging at Tufts University have shown that the flavonoids in berries can cross the blood-brain barrier in animals to improve brain function and even spur neurogenesis. They boost the growth of neurons and cell-to-cell communication in memory centers.
"Modern breeding focuses on qualities to attract the consumer," says Lila. "When we increase the size of a fruit, it is at the expense of the secondary components that would be greater in the wild plant."
The insults and injuries that plants endure in the wild—or the deliberate denial of excess fertilizer, pesticides, and water to cultivated crops—provoke their natural defenses and yield fruit that is seldom bigger but often richer than its commercial cousin. Any plant that survives environmental hardship— drought, extreme ultraviolet radiation, or cold temperatures, known collectively as abiotic stress—might not look the best or yield the most uniform and sizable fruit. But it tends to carry more flavor and nutrients, as well as flavonoids of such medicinal value they're often referred to as "nutraceuticals."
In parts of Alaska, the short, harsh growing season delivers extreme ultraviolet stress in the form of 23 hours of daylight—and tiny berries that, Lila reports, are "jam-packed with phytochemicals."
Studies by Agri-Food Canada show significantly higher amounts of anthocyanins in wild blueberries from the northernmost provinces of Canada than from southern provinces and the U.S. Both cold temperatures and UV radiation act there as abiotic stresses to boost flavonoid levels.
Stressing plants has a precedent in viticulture, where grapes are deliberately afflicted with botrytis, or "noble rot." It can impart character to the wine—but also kill off whole grape clusters. Such biotic stress (from a living organism) boosts resveratrol and other flavonoids more than tenfold in nearby uninfected grapes. Botrytis is being studied, along with the abiotic stress of artificial UV exposure, as a way to increase the bioactivity of fruits that might please our bodies more than our eyes.
Unlike the carotenoids in carrots and the anthocyanins of blueberries, most flavonoids are invisible. Like the quercetin lurking in apples and onions, they're stealth substances, detectable largely by their astringency—their pucker power. The European palate is more appreciative of such flavors than the sugar-addled American one. Bitter, not bigger, proves to be better.
Even in the great state of Texas, some scientists are big enough to think small. The Vegetable Improvement Center at Texas A&M University has developed the BetaSweet carrot, richer in pigments and flavonoids than traditional carrots, but less shapely. Scientists Daniel Leskovar and Kevin Crosby are working to develop cultivars prized more for their health-fortifying phytochemical content than for their looks or crop yield. "We stress the crop and see an increase of the carotenoids," Leskovar reports.
It will take some reeducation for Americans to accept the benefits of more modest-size produce. If greater concentrations of healthful phytochemicals and even better taste don't persuade, there's also the fact they're easier on the environment.
Plants, it turns out, are a lot like people. It typically takes some kind of challenge to bring out the best in them. —Daniel A. Marano
The Whole Damn Fruit
At the moment, exotic fruits such as the tropical açaí berry, Asian goji berries, and the American aronia berry (called chokeberry for its astringency) are enjoying cult status for their anthocyanin antioxidant content. But there are lots of phytochemicals in the market. Here's how to get them.
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