¿Te has preguntado si existe una manera natural de bajar tus niveles de presión arterial, protegerte contra el alzhéimer, perder peso y sentirte mejor? Resulta que sí la hay. El doctor Michael Greger (FACLM), fundador de NutritionFacts.org y autor del rotundo éxito de ventas del New York Times "How Not to Die" (Comer para no morir), nos presenta la nutrición basada en la evidencia para añadir años a nuestra vida y vida a nuestros años.

Hello and welcome to Nutrition Facts.  I’m your host, Dr. Michael Greger.  Today, we’re going to explore smart nutrition choices based, naturally, on facts.  Have a history of high blood pressure in your family?  How about heart disease?  Diabetes?  There are foods we can eat that may not only help prevent many of these chronic diseases but even stop them in their tracks. 

Today, we’re going to talk about urinary tract health – and some of the causes of urinary tract infections. 

Bacteria creeping up from the rectum into the urethra are the major cause of UTIs. But where does this rectal reservoir of bladder-infecting E. coli coming from in the first place? DNA fingerprinting point the blame at chicken.

In fact, half of retail poultry samples test positive for fecal contamination. Even worse, since chickens are given antibiotics, the strains of E. coli found in chicken are often drug-resistant.  Here’s more. 

Where do bladder infections come from? Back in the ‘70s, longitudinal studies of women over time showed that the movement of rectal bacteria up into the vaginal area preceded the appearance of those same types of bacteria in their urethra before they infected the bladder. But, it would be another 25 years before genetic fingerprinting techniques were able to confirm this so-called fecal-perineal-urethral theory—indicating that, indeed, it’s the “E.coli strains residing in the rectal flora [that] serve as a reservoir for urinary tract infections.”

Yet, it would be another 15 years still before we tracked it back another step, and figured out where that rectal reservoir of bladder-infecting E.coli was coming from—chicken.

Researchers were able to capture these extraintestinal (meaning outside of the gut), pathogenic, disease-causing E. coli straight from the slaughterhouse, to the meat, to the urine specimens obtained from infected women. We now have “proof of [a] direct link” between farm animals, meat, and bladder infections—”solid evidence that [urinary tract infections can be a] zoonosis.” Urinary tract infections as an animal-to-human disease. And, UTIs; we’re talking millions of women infected a year, costing over a billion dollars.

Even worse, the detection of multidrug-resistant strains of E. coli in chicken meat resistant to some of our most powerful antibiotics.

The best way to prevent bladder infections is the same way you best prevent all types of infections—by not getting infected in the first place. It’s not in all meat equally; beef and pork appear significantly less likely to harbor bladder-infecting strains than chicken.

Can’t you just use a meat thermometer, and cook chicken thoroughly? We’ve known for 36 years that it’s not always the meat, but the cross-contamination. If you give people frozen chickens naturally contaminated with antibiotic-resistant E. coli, let people prepare and cook it in their own kitchen as they normally would, and, poof—the bacteria ends up in their rectum, ready to cause trouble. In fact, five different strains of antibiotic-resistant E. coli jumped from the chicken to the volunteer.

And, they know it was cross-contamination, because the jump happened after the animal was prepared, but before it was eaten. Not only did it not matter how well the chicken was cooked; it didn’t even matter if you eat any! It’s the bringing of the contaminated carcass into the home, and handling it.

Within days, the drug-resistant chicken bacteria had multiplied to the point of becoming a major part of the person’s fecal flora in their gut. Here’s all this drug-resistant bacteria colonizing this person’s colon, yet the person hadn’t taken any antibiotics—it’s the chickens who were given the drugs. That’s why the industry shouldn’t be routinely feeding chickens antibiotics by the millions of pounds a year, because it can end up selecting for, and amplifying, superbugs that may end up in our body.

What if you’re really careful in the kitchen? “The effectiveness of hygiene procedures for prevention of cross-contamination from chicken carcasses in the domestic kitchen.” They went into five dozen homes, gave them each a chicken, and asked them to cook it. Now, I expected to read that they inoculated the carcass with a specific number of bacteria to ensure everyone got a contaminated bird, but no. They realized that fecal contamination of chicken carcasses was so common that they just went to the store, and bought any random chicken for people.

Now, after they were done cooking it, there was bacteria from chicken feces—Salmonella, Campylobacter—both serious human pathogens, everywhere, on the cutting board, utensils, on their hands, on the fridge handle, cupboard, oven handle doorknob.

But this was before they cleaned up. What about after cleaning? Still, pathogenic fecal bacteria everywhere.

Okay, fine. Obviously, people don’t know what they’re doing in the kitchen. So, they took another group of people, and gave them specific instructions. After you cook the chicken, you have to wash everything with hot water and detergent. They were told specifically: wash the cutting board, knobs on the sink, the faucet, the fridge, the doorknobs, everything. Okay. And, the researchers still found pathogenic fecal bacteria everywhere. Fine. Okay.

Last group. This time, they were going to insist that people bleach everything. The dishcloth immersed in bleach disinfectant, and then they spray the bleach on all those surfaces. Let the bleach disinfectant sit there for five minutes. And, they still found Campylobacter and Salmonella on some utensils, a dishcloth, the counter around the sink, and the cupboard. Definitely better, but still, unless our kitchen is like some biohazard lab, the only way to guarantee we’re not going to leave infection around the kitchen is to not bring it into the house in the first place.

The good news is that it’s not like you eat chicken once, and you’re colonized for life. In this study, the chicken bacteria only seemed to last about ten days.

The problem is that people tend to eat chicken more than once every ten days, so they may be constantly reintroducing these chicken pathogens into their colon.

For example, if you start feeding people only sterilized meat that’s been boiled for an hour, within three weeks, there’s a 500-fold drop in the number of antibiotic-resistant bacteria passing through their bodies.

Cranberries may reduce the recurrence of urinary tract infections, but their role in treating infections is limited. Let me explain.

How could any bacteria cause a bladder infection without just getting flushed away, literally? Certainly, if you’re not drinking enough, or men who have prostate enlargement and can’t empty completely, leaving behind a stagnant pool. But, in most people, there should be a constant flow of water through there. Well, bladder infection-causing E. coli evolved these finger-like projections that they use to stick to the walls of the bladder, so they don’t get washed away. 

Almost 30 years ago now, it was demonstrated that if you drip cranberry juice on E. coli, they don’t stick as well. Grape juice doesn’t work, nor does orange or apple juice, or even white cranberry juice made from unripened berries. So, maybe it’s one of the red phytonutrients that’s doing it.

Even if it works in a Petri dish, though, we don’t pee cranberry juice. I mean, how do we know that the anti-adherence phytonutrients in cranberries are even absorbed through the gut, so they make it into the bladder? Well, subsequent studies showed that if you drip urine of someone who drank cranberry juice onto E. coli, you get the same anti-stick effect. Ah, well, now we’re getting somewhere.

Well, the best way to prevent infections is to not get infected in the first place— which may involve the avoidance of chicken, as I’ve already discussed, so you’re not constantly reinfecting yourself. But, if that doesn’t work, if your gut remains stubbornly colonized with these bad bladder bugs, various tested cranberry products appear to reduce the recurrence of bladder infections by about 35%. Not as effective as antibiotics, but cranberries don’t foster antibiotic resistance, and have fewer side effects.

There’s good evidence to suggest that cranberries are effective for prevention, but not as an effective treatment; that makes sense, right? Cranberries prevent the initial adherence, but, that occurs at the start of the infection. When the infection is present, it’s already stuck there. Then, there’s no clinical data to suggest that cranberries are effective in the treatment of urinary tract infections—meaning cranberries don’t work better than placebo. But, placebos work! For example, ibuprofen seems to work just as good as antibiotics for the treatment of uncomplicated urinary tract infections.

Now, some people you really do need to treat with antibiotics—pregnant women, children, men, those with kidney infections, systemic symptoms like nausea and vomiting. But, for most healthy women, bladder infections just go away on their own, without antibiotics.

So, all the women who drink cranberry juice and have their symptoms disappear may falsely attribute their recovery to the juice. But, when it comes to most UTIs, nothing works! Nothing, in fact, actually works—leading doctors to try to figure out how they can harness the placebo effect for themselves.

Based on the potential benefits of proper hydration such as reduced bladder cancer risk, how many cups of water should we strive to drink every day?  Here are some answers.


More than 2,000 years ago Hippocrates said, “If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health.” What does that mean when it comes to water? Water has been described as a neglected, underappreciated, and under-researched subject, but a lot of the papers extolling the need for proper hydration are funded by the bottled water industry. Turns out the often quoted “drink at least eight glasses of water a day” has little underpinning scientific evidence.

Where did they come up with that then? The recommendation was traced back to this 1921 paper, in which the author measured his own pee and sweat, and determined we lose about 3% of our body weight in water a day, which comes out to be about eight cups. Consequently, for the longest time, water requirement guidelines for humanity were based on just one person.

But now we have evidence suggesting not drinking enough water may be associated with falls and fractures, heatstroke, heart disease, lung disorders, kidney disease, kidney stones, bladder and colon cancer, urinary tract infections, constipation, dry mouth, cavities, decreased immune function, and cataract formation.

The problem with many of these studies, though, is that low water intake is associated with several unhealthy behaviors, such as low fruit and vegetable intake, more fast food, less shopping at farmers’ markets. And think about it—who drinks lots of water? Those that exercise a lot; so, may be no wonder they have lower disease rates.

Only large and expensive randomized trials could settle these questions definitively. But given that water cannot be patented, such trials seem unlikely; who’s going to pay for them? So we’re left with studies that link disease with low water intake. But are people sick because they drink less, or are they drinking less because they’re sick? There have been a few large prospective studies in which fluid intake is measured before disease develops. For example, a Harvard study of 48,000 men found that the risk of bladder cancer decreased by 7% for every extra daily cup of fluid one may drink. So, a high intake of water—like eight cups a day, eight times seven, may reduce the risk of bladder cancer by about 50 percent, potentially saving thousands of lives.

The accompanying editorial commented that strategies to prevent the most prevalent cancers in the West are remarkably straightforward in principle. To prevent lung cancer, quit smoking; to prevent breast cancer, maintain your ideal body weight and exercise; and to prevent skin cancer, stay out of the sun and, now, it seems that this seemingly simple way to reduce the risk of bladder cancer is just drink more fluids.

This is probably the best evidence we have for a cut off: 20,000 men and women in the Adventist Health Study—about half vegetarian, so were also getting extra water eating more fruits and vegetables–and those drinking five or more glasses of water a day had about half the risk of dying from heart disease compared to those who drank two or fewer glasses a day. And like the Harvard study, this protection was after controlling for other factors such as diet and exercise. So they suggest it was the water itself–perhaps by lowering blood viscosity, meaning blood thickness.

So, based on all the best evidence to date, authorities from Europe, the U.S. Institute of Medicine, and the World Health Organization recommend between 2 and 2.7 liters of water a day for women. That’s 8 to 11 cups a day for women, and 10 to 15 cups a day for men. Now but that’s water from all sources–not just beverages–and we get about a liter from food and the water our body actually makes. So these translate into a recommendation for women to drink 4 to 7 cups of water a day, and men 6 to 11, assuming only moderate physical activity at moderate ambient temperatures.

We can also get water from all the other drinks we consume, including caffeinated drinks, with the exception of stronger alcoholic drinks, like wines and spirits. Beer can leave you with more water than you started with, but wine actively dehydrates you. Note, though, in the cancer and heart disease studies I mentioned, the benefits were found only with increased water consumption–not other beverages–so unless you have conditions like heart or kidney failure, women should drink 4 to 7 cups of water a day and men should drink 6 to 11.

To see any graphs, charts, graphics, images, or studies mentioned here, please 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.

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free.  There are no ads, no corporate sponsorship. It’s strictly non-commercial. I’m 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.

Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.

This is an approximation of the audio content, contributed by Allyson Burnett.


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