Chapter 60
Exactly that, exactly there!
The foundation of the traditional Okinawan diet consisted of steamed sweet potatoes; simmered or steamed leafy greens and other vegetables; and soy, mostly in the form of tofu and miso soup. It is a widespread misconception that fish or other meat was part of this traditional diet, because when you look at what people on Okinawa actually ate, you realize that isn’t true. The United States occupied the island of Okinawa from 1945 to 1972, then it was returned to Japan, so we have dietary data on the local population in the US National Archives.
What did the more than 2000 residents of Okinawa eat back then? One percent fish, less than one percent other meat, and less than one percent dairy products and eggs—so more than 96 percent plants and only a few processed foods.
Food that consists of more than 90 percent whole plant foods is highly anti-inflammatory and highly antioxidant. When the blood of 100-year-old Okinawan residents was examined for oxidized fat, it clearly showed less damage from free radicals—and that even though the antioxidant enzymes were no more active than in other people. What may have been decisive were the additional antioxidants from the plant-based diet. On Okinawa, proportionally there were six- to twelvefold fewer deaths from heart disease than in the United States, two- to threefold fewer deaths from colon cancer, sevenfold fewer from prostate cancer, and a five-and-a-half-fold lower risk of dying from breast cancer.
The traditional cuisine was based not only on whole plant foods and was not only oriented toward vegetables in general, but one vegetable played a special role, namely purple and orange sweet potatoes.
Exactly that, exactly there!
Since the 17th century, people on Okinawa have eaten mainly sweet potatoes; 69 percent of their daily calories come from them. That could be one of the secrets of longevity on this island. A study in China that followed 14 000 men and women for an average of 14 years found that those who ate sweet potatoes had a significantly lower probability of early death (18 percent), even after adjusting the calculations for a whole range of dietary, lifestyle, and socioeconomic factors. No wonder. The consumer advocacy organization Center for Science in the Public Interest (CSPI) ranks the sweet potato among the healthiest foods on this planet—and perhaps one day outside the planet as well, because NASA has selected the sweet potato for its space missions.
Even in terms of the nutrient/value-for-money ratio, the sweet potato is an absolute super deal. A study of dozens of different types of vegetables found that some of the healthiest foods, like dark leafy greens, are also the most affordable, and the sweet potato is right at the top because you get the greatest amount of nutrients for your money. And the very, very best are purple sweet potatoes.
Anthocyanins are natural purple, red, and blue pigments in plants such as berries, grapes, plums, red cabbage, and red onions. In model organisms such as yeast, worms, flies, and mice, anthocyanins from red rice, black rice, and purple wheat have anti-aging and/or life-extending properties. In a direct comparison of plant pigments, the purple in the purple sweet potato was more strongly antioxidant than the pigments in grape skins, elderberries, red cabbage, and purple corn.
Even regular sweet potatoes have been proven in rats to be immediately and chronically anti-inflammatory, but the pigment in purple sweet potatoes can do even more—namely reverse or repair the damage that arose from inflammatory or oxidative processes in mouse brains. From the standpoint of anti-aging, the color compounds in purple sweet potatoes also reduce inflammation, increase autophagy, and slow the senescence of human blood vessel cells in the petri dish; in addition, in mice they stimulate sirtuin activity by boosting NAD+.
We suspect that the activation of autophagy is the reason for the 15-percent extension of life span in fruit flies when they are fed an extract of purple sweet potatoes; in addition, the age-related leaky gut syndrome decreases, so there is presumably also a benefit for health span. Researchers fed fruit flies blue food dye that colors the digestive tract of young flies but seeps out of the leaky guts of older flies, so that their whole body turns blue. The whole thing is called—no joke—the “Smurf experiment.” The number of “Smurf flies” was significantly lower in the group fed purple sweet potato extract.
Have any of these positive effects been demonstrated in clinical studies? For the anthocyanins of the purple sweet potato, studies with human fecal cultures have demonstrated prebiotic effects—namely the strong proliferation of good bacteria such as bifidobacteria and Lactobacillus; at the same time, there was an increase in protective short-chain fatty acids. That could explain the anti-inflammatory effects in the only placebo-controlled double-blind study I could find. Men with liver inflammation who were randomized to drink one cup a day of a smoothie with purple sweet potatoes had significantly improved liver function on tests eight weeks later compared with the men in the control group, who received a placebo drink with a similar appearance and taste.
Soy—yes, just so!
In the traditional Okinawan diet, soy is the main source of concentrated protein. The island’s residents ate an average of 90 grams of soy products per day—as mentioned, mostly in the form of tofu and miso—and thus their soy intake was among the highest in the world. Does that also play a role in their longevity? To what extent can science substantiate the old Asian saying, “Vegetables and tofu keep people healthy”?
For more than 20 years, soy’s protection against heart disease has been one of the rare “FDA-confirmed” claims about the health effects of a food. Randomized controlled trials have shown that consuming soy can lead to a slight decrease in risk factors for cardiovascular disease, such as blood pressure and cholesterol. As a billion-dollar business, “Big Soy” has enough money to pay for research meant to promote the benefits of its bean. But is soy really the top bean, or do other legumes have just as much to offer? As it turns out, other beans—for example lentils, lima beans, white beans, and pinto beans—can fight bad cholesterol just as efficiently as soy proteins—eight points less LDL cholesterol; with soy it’s five (mg/dl). However, if you look at the studies individually, it does indeed seem as though soy products such as soy milk and soybeans come out ahead, because on average they cause a drop in LDL levels of eleven points; with highly processed soy extracts it’s three points.
It appears that this results in a reduced risk of heart disease and stroke, as well as a lower risk of death from cancer and cardiovascular disease. However, a significant reduction in overall mortality was seen only in higher-quality studies, meaning those with at least 10 000 participants. Compared with the group that ate the least soy, the group with the highest intake of isoflavones (these are the natural phytoestrogens in soy) consistently showed a lower risk of early death. “Our findings,” the researchers concluded after the meta-analysis, “support current recommendations to eat more soy in order to live longer.”
What about the salt in miso?
A lot of salt is added during miso production, which is why I avoided miso for a long time—until I took a closer look at the whole thing. For details, read my chapter on beans in How Not to Die, but as it turned out, miso is not associated with the risk of stomach cancer that is suspected with the salt in other fermented foods like kimchi, and there is no risk of high blood pressure either. But what if you already have high blood pressure?