 Changes in your diet not only affect you physically, physiologically inside, but also mentally how will you think, psychologically how will you feel? But you'll never know just how good you can feel until you put it to the test and try eating healthier. Welcome to the Nutrition Facts Podcast, I'm your host, Dr. Michael Greger. Today we revel in the antioxidant properties of hibiscus tea, which compared to 280 common beverages ranks number one for its antioxidant content, even beating out green tea. In our first story, we look at the results of a randomized double-blind placebo-controlled trial of hibiscus tea for wheat loss. Hibiscus tea, also known as rosell or Jamaica, is enjoyed around the world hot or cold for its bright red color and tart cranberry-like flavor. It's the zing in red zinger tea. I talk about its benefits in the chapter on high blood pressure and how not to die, working as well as some leading anti-hypertensive medications in head-to-head tests, or even beating the drugs out. Within three hours of drinking hibiscus tea, changes in hundreds of metabolites can be detected in the human bloodstream with creative names like hibiscus acid, or hibiskin, or hibisitrin. Alterations in human gene expression of the three-hour mark after drinking it suggest a down-regulation of cholesterol synthesis and an improvement in metabolism, but randomized controlled trials failed to consistently find cholesterol-lowering benefits. An interesting side effect popped up, though—weight loss. In Mexico, hibiscus tea has been traditionally used as a treatment for obesity, sparking lots of research interest. Computer modeling studies have suggested that certain hibiscus compounds might bind to the fat-digesting enzyme lipase, like a locking key. Test tube studies screening a variety of medicinal plants did indeed find hibiscus-inhibited lipase more than most of the others, and hibiscus has been found to reduce body fat in hamsters, mice, and rats, increasing fecal fat excretion, but it wasn't tested in people until this study published in 2014. Spoiler alert, hibiscus can inhibit obesity and fat accumulation in humans, and improve fatty liver. To create a randomized double-blind trial, instead of trying to create some artificially colored and flavored placebo tea, they just dried the hibiscus tea into powder and put it into capsules. After 12 weeks, there was a greater reduction in waistlines and percent body fat in the hibiscus group compared to those who got placebo capsules, but the dose they ended up using was equivalent of like 9 cups of hibiscus tea a day. I recommend people stick to no more than a quarter day on a regular basis due to the high manganese content. Manganese is an essential trace mineral, but 9 cups a day might result in too much of a good thing. Finally, in 2018, this study was published using a reasonable dose, the equivalent of about a single 12-ounce glass of hibiscus tea a day. The complicating factor is that they also added lemon verbena to the mix, that's another herbal tea, better known for improving recovery after intense bouts of strength training, but there was some promising in vitro data on effects of lemon verbena on fat cells in a petri dish, so they tried a combination. It comes out to be about a cup and a half of hibiscus tea and a quarter cup of lemon verbena tea once a day for two months. Both the tea and placebo groups were fed diets containing the same amount of calories, yet those randomized to the tea group lost significantly more weight, five pounds, compared to three pounds. That's only an extra pound or two a month, but an extra pound a month eating this same number of calories. That's the advantage of fat-blocking interventions that actually cause you to lose more calories beyond just reducing hunger and making you feel fuller longer in hopes you'll eat fewer calories in the first place. Why not just pop pills instead of brewing tea? There's all sorts of herbal extract supplements on the market, but that presumes we know enough to extract out the right active ingredients. For example, it does not appear to be the red anthocyanin pigments in hibiscus, since white varieties seem to have similar effects. When the various compounds in hibiscus tea are isolated out and tested in various combinations, synergistic effects are found, meaning the whole may be greater than the sum of its parts. As with any sour food or beverage though, like after eating citrus, it's important to wash the natural acids off your teeth by rinsing your mouth out with water to protect your tooth enamel. You also want to wait at least an hour before brushing, so as not to erode your enamel when it's in a softened state. In our next story, we look at how the blood pressure lowering effects of hibiscus tea compared to the dash diet, a plant-based diet, and long-distance endurance exercise. The latest research pitted hibiscus against obesity, giving hibiscus to overweight individuals, and showed reduced body weight. But after 12 weeks on hibiscus, they only lost like three pounds, and really only one and a half pounds over placebo. Clearly no magic fix. The purported cholesterol-lowering property of hibiscus tea looked a bit more promising. Some older studies suggested as much as an 8% reduction, drinking two cups a day for a month. But when all the studies are put together, the results were pretty much a wash. This may be because only about 50% of people respond at all to drinking the covenant between two to five cups a day. Though those that do respond may get a respectable 12% or so drop in cholesterol, but nothing like the 30% drop one can get within weeks of eating a healthy enough plant-based diet. High blood pressure is where hibiscus may really shine, disease affecting a billion people, killing millions. Up until 2010, there wasn't sufficient high-quality research out there to support the use of hibiscus tea to treat it, but there are now randomized, double-blind, placebo-controlled studies where hibiscus tea is compared to artificially colored and flavored water that looks and tastes like hibiscus tea, and the tea did significantly better. We're still not sure why it works, but hibiscus does appear to boost nitric oxide production, which could help our arteries relax and dilate better. Regardless, an updated review acknowledged that the daily consumption of hibiscus tea may indeed significantly lower blood pressures in people with hypertension, but by how much? How does this drop in blood pressure compare to other interventions? Well, the premier clinical trial, when it comes to comprehensive lifestyle modification for blood pressure control, is the premier clinical trial. Realizing that 9 out of 10 Americans are going to develop hypertension, they randomized 800 men and women with high blood pressure into one of three groups. One was the control group, the so-called advice-only group, where patients were just told to lose weight, cut down on salt, increase exercise, and eat healthier. In the two behavioral intervention groups, they got serious, 18 face-to-face sessions, group meetings, food, diaries, monitored physical activity, calorie and sodium intake. Now, one intervention group just concentrated on exercise, and the other one included exercise and diet. They pushed the dash diet, high fruits and vegetables, and low and full-fat dairy products and meat, and in six months achieved a 4.3-point drop in systolic blood pressure compared to control, slightly better than the lifestyle intervention without the diet. Now, a few points might not sound like a lot. That's like someone going from a blood pressure of 150 over 90 to a blood pressure of 146 over 90, but on a population scale, a 5-point drop in the total number could result in a 14% fewer stroke deaths, 9% fewer fatal heart attacks, and 7% fewer deaths every year overall. But a cup of obiscus tea with each meal didn't just lower blood pressure by 3, 4, 5 points, but by 7 points, you know, 129 down to 122. In fact, tested head-to-head against a leading blood pressure drug called captupril, two cups of strong obiscus tea every morning, using a total of 5 tea bags for those two cups, was as effective in lowering blood pressure as a starting dose of 25 mg of captupril taken twice a day. So, as good as drugs without the drug side effects and better than diet and exercise? Well, the lifestyle interventions were pretty wimpy, as public health experts noted. The premier study was only asking for 30 minutes of exercise a day, whereas the World Health Organization is more like an hour-day minimum. And diet-wise, the lower the animal fat intake and the more plant sources of protein the premier participants were eating, the better the diet appeared to work, which may explain why vegetarian diets appear to work even better. And the more plant-based, the lower the prevalence of hypertension. On the DASH diet, they were told to cut down on meat, but were still eating meat every day, so would qualify as the non-vegetarians here in the Adventist II study, which looked at 89,000 Californians, and found that those who instead only ate meat on more like a weekly basis had 23% lower rates of high blood pressure, cut out all meat except fish, and the rate is 38% lower. Cut out all meat period, the vegetarians, have less than half the rate, and the vegans cutting out all animal protein and fat appeared to have thrown three quarters of their risk of this major killer out the window. One sees the same kind of stepwise drop in diabetes rates as one's diet gets more and more plant-based, and a drop in excess body weight such that only those eating completely plant-based diets fell into the ideal weight category. But could that be why those eating plant-based diets have such great blood pressure? Maybe it's just because they're so skinny on average. I've shown previously how those eating plant-based diets have just a fraction of the diabetes risk even at the same weight, even after controlling for BMI. But what about hypertension? The average American has what's called pre-hypertension, which means the top number of your blood pressure between 120 and 139. Not yet hypertension, which starts at 140, but it means we may be well on our way. Compare that to the blood pressure of those eating whole food plant-based diets. Not three points lower, four points lower, or even seven points lower, but 28 points lower. Now, but the group here eating the standard American diet was, on average, overweight, with BMI over 26. Still better than most Americans, but while the vegans were a trim 21, that's 36 pounds lighter. So maybe the only reason those eating meat, eggs, dairy, and processed junk had such higher blood pressure was because they were overweight. Maybe the diet per se had nothing to do with it. To solve that riddle, we would have to find a group, still eating the standard American diet, but as slim as a vegan. To find a group that fit and trim, they had to use long-distance endurance athletes who ate the same crappy American diet, but ran, on average, 48 miles a week for 21 years. They ran almost two marathons a week for 20 years. So if you do that, anyone can be slim as a vegan, no matter what they eat. So it appears if you run about a thousand miles every year, you can start to rival some couch potato vegans. Doesn't mean you can't do both, but it may be easier to just eat plants. Finally today, the impressive manganese content of hibiscus tea may be the limiting factor for safe daily levels of consumption. Over-the-counter antacids are probably the most important source for human aluminum exposure in terms of dose. Melox, for example, taken as direct to, can exceed the daily safety limit more than 100-fold, and nowhere on the label does it say not to take with acidic beverages such as fruit juice. Washing an acid down with orange juice, for example, can increase aluminum exposure 8-fold, and citric acid was worse, the acid found naturally concentrated in lemons and limes. Just as sour fruits can enhance the absorption of iron, which is a good thing, through the same mechanism, they may enhance the absorption of aluminum. Raising the question, what happens when one adds lemon juice to tea? Previously, I concluded that the amount of aluminum and tea is not a problem for most people, because it's not very absorbable. But what if you add a lemon? No difference between tea with lemon, tea without lemon, or no tea at all in terms of the amount of aluminum in the bloodstream, suggesting that tea drinking does not significantly contribute to aluminum actually getting inside the body, the lemon juice or not. Now they're talking about black tea, green tea, white tea, oolong tea. What about the red-zinger herbal tea, hibiscus? The reason it's called sour tea is because it has natural acids in it, like citric acid. Might that boost the absorption of any of its aluminum? Well, a greater percentage of aluminum gets from the hibiscus into the tea water, but there's less aluminum overall. The question is, does the aluminum then get from the tea water into our body? We don't have that data, so to be on the safe side, we should assume the worst, that the hibiscus tea aluminum, unlike green or black tea aluminum, is completely absorbable. In that case, based on this data, in the World Health Organization Weekly Safety Lemon, we may not want to drink more than, like, 15 cups of hibiscus tea a day. That's based on someone who's about 150 pounds, but so if you have a 75-pound year or 10-year-old, a half gallon of tea a day may be theoretically too much. And more extensive testing more recently suggests levels may be as high as twice as much, so no more than about two quarts a day for adults, or a quart a day for kids every day, or pregnant women. And hibiscus tea should be completely avoided by infants under six months, who should only be getting breast milk anyway, as well as kids with kidney failure, who can't efficiently excrete it. The study also raised concern about the impressive manganese level in hibiscus tea. Manganese is an essential trace mineral, vital component of some of our most important antioxidant enzymes, but we probably only need two to five milligrams a day, and four cups of hibiscus tea can have as much as 17, averaging about 10. Is that a problem? Well, women given 15 a day for four months, if anything, only saw an improvement in their anti-inflammatory antioxidant enzyme activity. This study, using 20 a day, similarly showed no adverse short-term effects, and importantly showed that the retention of dietary manganese is regulated. Our body's not stupid. If we take too much in, our body decreases the absorption and increases the excretion. So even though tea drinkers may drink 10 times more manganese, get 10 times more a day, 10 or 20 milligrams a day, the levels in their blood is essentially identical. So there's little evidence that dietary manganese poses a risk. That was regular tea, though. We don't know about the absorption from hibiscus. So there on the side of costume, we should probably not routinely exceed the reference dose of 10 milligrams per day. So that's only about a quart a day for adults, half a quart for a 75-pound child. So that's actually changed my family's consumption. Given the benefits of the stuff, I was using it as a substitute for drinking water, so like two liters a day. And I was blending the hibiscus petals in, not throwing them away, effectively doubling aluminum content and increasing manganese concentrations by about 30%. So given this data, I've cut back to no more than about a quart of filtered hibiscus tea a day. 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 be able to share it on social media to help inspire others. If you'd like to see any of the graphs, charts, graphics, images, or studies mentioned here, go to the Nutrition Facts Podcast landing page. There you'll find all the detailed information you need, plus links to all the sources we cite for each of these topics. My last two books were a How to Survive a Pandemic and my How Not to Diet Cookbook. Get ready this year for the launch of How Not to Age, and of course all the proceeds for the sales of all my books goes directly to charity. NutritionFacts.org is a non-profit, science-based public service. We can sign up for free daily updates on the latest new nutrition research with bite-sized videos and articles uploaded nearly every day. Everything on the website is free. There are no ads, no corporate sponsorships, no kickbacks, it's strictly non-commercial, not selling anything. I just put it up as a public service as a labor of love as a tribute to my grandmother, whose own life was saved with evidence-based nutrition.