 It's crazy when you think about all the different kinds of foods we eat. We just swallow and hope it all works out for the best. Well, it turns out there are better ways to think about keeping our bodies humming healthfully along. Welcome to Nutrition Facts, I'm your host, Dr. Michael Greger. Today we discover the powerful properties of citrus. I'm talking lemons, lime, citrons, bitter orange, grapefruit, pomelo, mandarin, grapefruit, and kumquats. Actually, one of my favorite citrus fruits is the kumquat, because you can eat the whole fruit peel and all, which is ideal because the DNA-repairing enzyme-boosting powers of citrus appear to be concentrated in the peel. New data demonstrating a DNA-protective agent was present at least some fruits and vegetables, found that it was heat-sensitive and determined it was not vitamin C, confirmed in a study that tried vitamin C directly, and found no effect on DNA protection and repair of DNA strand breaks. The crotinoid beta-cryptozanthin found primarily in citrus seems at least one candidate. If you expose cells to a mutagenic chemical, you can cause physical breaks in the strands of DNA, but in less than an hour our DNA-repair enzymes can weld most of our DNA back together. But if you add some of that citrus phytonutrient, you can effectively double the speed at which DNA is repaired. But this is all just cells in a Petri dish. What about in a person? If you have people drink a glass of orange juice and draw their blood two hours later, the DNA damage you can induce with an oxidizing chemical drops, whereas if they just had like orange Kool-Aid, didn't help. So, do people who eat more fruit walk around with less DNA damage? Yes, particularly in women. Does this actually translate into lower cancer rates? It appears so. Citrus alone associated with a 10% reduction in odds of breast cancer. Given to newly diagnosed breast cancer patients, citrus phytonutrients were found to concentrate in breast tissue, though many complained of citrus burps due to the concentrated extract they were given. So, researchers evaluated topical application as an alternative dosing strategy, recruiting women to apply orange-flavored massage oil to their breasts daily. This request was met with excellent compliance, but it didn't work. We actually have to eat our food. Why not just take carotenoid supplements to boost our DNA repair? Because it doesn't work. Although dietary supplements did not provoke any alteration in DNA repair, dietary supplementation with carrots did. This suggests that the whole food may be important in modulating DNA repair processes. Though orange juice consumption was found protective against childhood leukemia, it was not found protective against skin cancer. However, the most striking feature was the protection purported by citrus peel consumption. Who eats orange peels? Lots of people, evidently. Just drinking orange juice may increase the risk of the most serious type of skin cancer, daily consumption associated with a 60% increase in risk. So again, better to stick with the whole fruit, and you can eat citrus extra whole by zesting peel into your dishes. Next, we look at how phytonutrients in citrus, such as hisperidin, increase blood flow sufficient to warm the hands and feet of those with cold sensitivity. In 1936, Albert Sanyurgi, who won the Nobel Prize for discovering vitamin C, described a vitamin P, which we now know encompasses a class of thousands of phytonutrients called flavonoids. Some, like quercidin, are widespread in plant-based foods. You can tell something is widespread in the plant kingdom when you can even find it in iceberg lettuce. Others, however, are only found in specific plant families. For example, hisperidin is found primarily in citrus fruits. This may be one of the reasons out of all the different types of fruits that have been looked at, citrus may help cut our risk of stroke the most. The citrus phytonutrient hisperidin increases blood flow. Using a machine called a Doppler fluximeter, you can measure blood flow through the skin using a laser beam. A laser Doppler fluximeter sounds like something from back of the future. And if you give people the amount of hisperidin found in two cups of orange juice, blood flow goes up, though if you instead just give them the orange juice itself, that works even better. So there's other beneficial stuff besides just the hisperidin in citrus. For example, if you measure the changes in genetic expression, orange juice consumption induces changes in the expression in 3,000 of our genes, whereas hisperidin alone only modulated the expression of about 2,000. Still, nearly 2,000 stretches of our DNA expressed differently because we consumed just one of the thousands of phytonutrients and plants, pretty mind-blowing. And these changes in blood flow are not just kind of in theory. Researchers have taken volunteers with cold sensitivity, cold hands, cold feet, put them in an air-conditioned room, and measured the temperature of their fingertips after drinking a placebo drink, like orange Kool-Aid, versus drinks with two doses of actual citrus phytonutrients. In the Kool-Aid group, their fingers got colder and colder, dropping nearly 9 degrees Fahrenheit, but the fingers of those consuming low or high doses of citrus didn't as much. That's because their blood flow remained steady. When we're exposed to cold temperature, our body starts to clamp off peripheral blood flow to keep our core warm, but if you eat a bunch of oranges before you go skiing, your risk of frostbite may go down since you're keeping up your blood flow to your fingers and toes. They even took these poor women and plunged their hands into some chilly water. Their finger temperature rebounded faster towards normal in the citrus group. Of course, having warm hands is nice, but maintaining blood flow to your fingers is not as important as maintaining blood flow to your brain. Finally, today we look at how daily citrus fruit consumption during athletic training may reduce muscle fatigue as evidenced by lower blood lactate concentration. The same lactic acid that makes yogurt tangy is the same lactic acid that builds up in our muscles when we exercise strenuously. Instead of bacteria fermenting the sugar and milk to make energy for themselves, our muscles ferment sugar in our diet to produce energy to contract. If, like when we're sprinting, lactic acid builds up in our muscles faster than it can be removed, we can end up with a burning sensation in our muscles, forcing us to stop. Now, if we train, we can increase the number of blood vessels in our muscles and clear out the lactate faster. For example, if you take some overweight sedentary women and start them on an aerobic training program of running and walking, at the end of three months their lactate levels during exercise decrease 17%, but those on the same program who drank two cups of orange juice a day decreased their levels 27%. They did the same exercise program, but the citrus group experienced a significant decrease in blood lactate concentration signifying improvement in physical performance with less muscle fatigue. I don't recommend drinking juice because you're losing all that wonderful fiber that slows the rate of fruit sugar absorption into our system, so the whole fruit is nearly always better than fruit juice. Now, this is not to say OJ isn't better than Coke. OJ has those citrus phytonutrients like hasperidin, which may be why the women's triglycerides didn't go up, even though they were drinking two cups of fruit juice every day. Hasperidin may actually help lower our digestion of fats, but once you get up to three cups a day of juice, you can really start bumping up your triglycerides. We would love it if you could share with us your stories about reinventing your health through evidence-based nutrition. Go to nutritionfacts.org slash testimonials. We may share it on our social media to help inspire others. To see any graphs, charts, graphics, images, or studies mentioned here, please go to the nutritionfacts podcast landing page. 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