¿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.

Welcome to Nutrition Facts. I’m your host, Dr. Michael Greger, and I’m here to ask you: What is the most important decision you’ll make today? Is it how you’ll get to work, who you’ll set up a meeting with, what friend you’ll call for lunch? Well, as it turns out, probably the most important decision you’ll make today is what to eat. What we eat on a day-to-day basis is the number one determinant of our health and longevity—literally. Most premature deaths in the United States are preventable and related to nutrition. So, we’re going to explore some smart nutrition choices based, naturally, on facts. Here, we refer to the science, the research, the available data published in the peer-reviewed medical literature right now. That’s why I wrote my book, “How Not to Die”, and why I created my nonprofit site NutritionFacts.org and, now, this podcast.

Today, we’ll look into the science on the right kinds and amounts of protein in our diets. As pointed out by the Chair of Harvard’s Nutrition Department, plant protein is preferable to animal protein because food is a package deal. Unlike protein from animal sources, protein from plants has been associated with lower rates of chronic disease.

But, in the 1950’s, the field of nutrition got human protein requirements spectacularly wrong, leading to a massive recalculation. Here’s the story.

There has been a history of enthusiasm for protein in the nutrition world. A century ago, the protein requirements were more than twice what we know them to be today. This enthusiasm peaked in the 1950s, with the United Nations identifying protein deficiency as a serious widespread global problem. There was a protein gap that needed to be filled. This was certainly convenient for the U.S. dairy industry, who could dump their postwar surplus of dried milk onto the third world, rather than having to just bury it. But, this led to the great protein fiasco. There was a disease of malnutrition, called kwashiorkor, that was assumed to be caused by protein deficiency, famously discovered by Dr. Cicely Williams, who spent the latter half of her life debunking the very condition that she first described.

Turns out there’s no real evidence of dietary protein deficiency. The actual cause of kwashiorkor remains obscure, but fecal transplant studies suggest changes in gut flora may be a causal factor. How could the field of nutrition have gotten it so spectacularly wrong? A famous editorial about the profession started with these words: “The dispassionate objectivity of scientists is a myth. No scientist is simply involved in the single-minded pursuit of truth, he or she is also engaged in the passionate pursuit of research grants and professional success. Nutritionists may wish to attack malnutrition, but they also wish to earn their living in ways they find congenial.” This inevitably encourages researchers to “make a case” for the importance of their own portion of the field, and “their nutrient,” which was protein.

Science eventually prevailed, though, and there was massive recalculation of human protein requirements in the 1970s, which “at the stroke of a pen” closed the so-called “protein gap,” and destroyed the theory of this pandemic of “protein malnutrition.” Infant protein requirements went from a recommended 13% of daily calories, down to 10%, then 7%, and then down to 5%; however, to this day, there are still those obsessing about protein. Those promoting Paleolithic diets, for example, try to make the case for protein from an evolutionary perspective.

Okay, so let’s ask the question: What is the perfect food for human beings, the food that was fine-tuned just for us over millions of years to have the perfect amount of protein? Human breast milk. If high-quality protein was the “nutrient among nutrients,” helping us build our big brains over the last few million years, one would expect that importance to be resoundingly reflected in the composition of human breast milk—especially since infancy is the time of our most rapid growth.

But this is patently not the case. Human breast milk is one the lowest-protein milks in the mammalian world. In fact, it may have the lowest protein concentration of any animal in the world—less than 1% protein by weight. This is one of the reasons why feeding straight cow’s milk to babies can be so dangerous. The protein content in human milk is described as extremely low, but it’s not low at all, it’s right where it needs to be. That’s the natural, normal level for the human species fine-tuned over millions of years.

Adults require no more than 0.8 or 0.9 grams of protein per healthy kilogram of body weight per day. So, that’s like your ideal weight in pounds, multiplied by four, and then divided by ten. So, someone whose ideal weight is 100 pounds may require up to 40 grams of protein a day. On average, they probably only need about 30 grams a day, which is .66 grams per kilogram, but we say 0.8 or 0.9 because everyone’s different, and we want to capture most of the bell curve.

People are more likely to suffer from protein excess than protein deficiency. The adverse effects associated with long-term high protein diets may include disorders of bone and calcium balance, disorders of kidney function, increased cancer risk, disorders of the liver, and worsening of coronary artery disease. Therefore, there is currently no reasonable scientific basis to recommend protein consumption above the current recommended daily allowance, due to its potential disease risks.

Which type of protein is better for our kidneys? Powerful anti-inflammatory drugs can abolish the hyperfiltration and protein leakage response to meat ingestion, suggesting that animal protein causes kidney stress through inflammation. Here is the research. 

Between 1990 and 2010, some of our leading causes of death and disability haven’t changed. Heart disease was the leading cause of loss of life and health then and remains the leading cause today. Some things got better, like HIV/AIDS, but others got worse, like chronic kidney disease, a doubling in the tens of thousands of deaths and the hundreds of thousands whose kidneys fail completely, requiring kidney transplants or lifelong dialysis. About one in eight of us now have chronic kidney disease whether we know it or not and, most of those with kidney disease don’t know it, about three-quarters of the millions affected are unaware their kidneys are starting to fail. This particularly worrisome given that early identification provides an opportunity to slow the progression and alter the course of disease. So, what can we do about it?

The Western-style diet is a major risk factor for impaired kidney function and chronic kidney disease, also known as the Meat-Sweet Diet, or Standard American Diet, causing an impairment of kidney blood flow, inflammation, and subsequent leakage of protein in the urine, and a rapid decrease in kidney function. Table sugar and high-fructose corn syrup are associated with increased blood pressure and uric acid levels that can both damage the kidney and saturated fat, trans fat, and cholesterol found in animal fat and junk food negatively impact kidney function as well. The consumption of animal fat can actually alter the structure of the kidney and animal protein can deliver an acid load to the kidneys, increase ammonia production, and damage the sensitive kidney cells. That’s why restricting protein intake is recommended for preventing kidney function decline, though it may be animal protein in particular, not just protein in general; so, the source of the protein, plant versus animal, may be more important than the amount regarding adverse health consequences.

Animal protein intake has a profound effect on normal human kidney function, inducing what’s called hyperfiltration, increasing the workload of the kidney.

This may help explain why our kidneys fail so often. Unlimited intake of protein-rich foods, now generally regarded as “normal,” may be responsible for dramatic differences in kidney function between modern human beings and their remote predecessors who hunted and scavenged for meat here and there. Sustained, rather than intermittent, excesses of protein require us to call on our kidney reserves continuously, causing a kind of unrelenting stress on our kidneys that can predispose even healthy people to progressive kidney scarring and deterioration of kidney function. It’s like always revving our engine into the red. On the other hand, administration of an equal quantity of vegetable protein does not appear to have the same effects.

Eating meat, for example, increases the workload on the kidneys within hours of consumption but, apparently, taking care of plant protein appears to be a cinch. This was done with beef, but any animal protein will do. Eat a meal of tuna fish, and you can see the increased pressure on the kidneys go up, again, within just hours, for both non-diabetics with normal kidneys and diabetics with normal kidneys. If, instead of having a tuna salad sandwich, you had a tofu salad sandwich with the same amount of protein, no effect and, same thing happens with eggs and dairy protein, both in people with normal and diseased kidneys.

Short-term studies have indicated that substituting plant proteins, like soy, for animal protein is associated with less hyperfiltration and protein leakage, therefore, slowing deterioration of kidney function. However, the long-term effect had not been adequately studied, until this study: A 6-month, double-blind, randomized, placebo-controlled trial, soy versus dairy protein, and the consumption of whole soy tended to preserve renal function, kidney function, compared with milk in individuals with lowered renal function. Similar results were reported in diabetics. Even just giving isolated soy protein appeared to make things better, compared to dairy protein, which made things worse.

Once one’s kidneys have deteriorated to the point that they’re actively losing protein in the urine, a plant-based diet may help turn it off and on, like a light switch. What is going on? Why does animal protein cause that overload reaction, but not plant protein? It appears to be an inflammatory response triggered by the animal protein. We know this because administration of a powerful anti-inflammatory drug abolishes the hyperfiltration, protein leakage response to meat ingestion, confirming the role of inflammation in the impact of animal protein on our kidneys.

Only about one in 10,000 people make it to be 100 years old, which raises the question: What’s their secret?  Well, in 1993, a major breakthrough in longevity research was published: A single genetic mutation that doubled the lifespan of a tiny roundworm. Instead of all being dead by 30 days, the mutants lived 60 days or longer. This lifespan extension was the largest yet reported in any organism.

This Methuselah worm medical marvel is the equivalent of producing a healthy 200-year-old human—all because of a single mutation? That shouldn’t happen; I mean, presumably, aging is caused by multiple processes, many genes. How could just knocking out one gene double the lifespan?

What is this aging gene anyway, this gene that so speeds up aging that if it’s knocked out the animals live twice as long? It’s been called the Grim Reaper gene. What is it? It’s the worm equivalent of the human IGF-1 receptor and mutations of that same receptor in humans may help explain why some people live to be a hundred, and other people don’t.

So, is it just the luck of the draw whether we got good genes or bad? No, we can turn on and off the expression of these genes, depending on what we eat. Three years ago, I profiled a remarkable series of experiments about IGF-1 (insulin-like growth factor 1), this cancer-promoting growth hormone, released in excess amounts by our liver when we eat animal protein. So, men and women who don’t eat meat, egg white, or dairy proteins have significantly lower levels circulating within their bodies.

Switching people to a plant-based diet can significantly lower IGF-1 levels within just 11 days, markedly improving the ability of women’s bloodstreams to suppress breast cancer growth, and then kill breast cancer cells off.

Similarly, the blood serum of men on plant-based diets suppresses prostate cancer cell growth about eight times better than before they changed their diet. This dramatic improvement in cancer defenses is, however, abolished if you add back just the amount of IGF-1 banished from their systems because they were eating and living healthier.

This is one way to explain the low rates of cancer among plant-based populations: the drop in animal protein intake leads to a drop in IGF-1, which leads to a drop in cancer growth. An effect so powerful, Dr. Dean Ornish and colleagues appeared to be able to reverse the progression of early stage prostate cancer without chemo, surgery, or radiation—just a plant-based diet and other healthy lifestyle changes.

Now, when we’re kids, we need growth hormones to grow. There’s a rare genetic defect that causes severe IGF-1 deficiency, leading to a type of dwarfism—but also apparently makes you effectively cancer-proof. Not a single death from cancer in about 100 individuals with IGF-1 deficiency. How about 200 individuals? None developed cancer. See, most malignant tumors are covered in IGF-1 receptors but, if there’s no IGF-1 around, then they may not be able to grow and spread.

This may help explain why those eating low-carb diets appear to cut their lives short but not just any low-carb diet—specifically those based on animal sources, whereas vegetable-based low-carb diets were associated with a lower risk of death.

But look, low-carb diets are high in animal fat, as well as animal protein. So, how do we know it wasn’t the saturated animal fat that was killing people off and it had nothing to do with the protein? What we need is a study that just follows a few thousand people and their protein intakes for 20 years or so and just see who lives longest, who gets cancer, who doesn’t. But, there’d never been a study like that—until now.

Six thousand men and women over age 50 from across the U.S. followed for 18 years and those under age 65 with high protein intakes had a 75% increase in overall mortality and a fourfold increase in the risk of dying from cancer–but not all proteins, these associations were either abolished or attenuated if the proteins were plant-derived, which all makes sense, given the higher IGF-1 levels among those eating lots of animal protein.

The sponsoring university sent out a press release with a memorable opening line: “That chicken wing you’re eating could be as deadly as a cigarette,” explaining that eating a diet rich in animal proteins during middle age makes you four times more likely to die from cancer than someone with a low-protein diet—a mortality risk factor comparable to smoking cigarettes. And when they say low-protein diet, what they actually mean is just getting the recommended amount of protein.

“Almost everyone is going to have a cancer cell or a pre-cancerous cell in them at some point.” The question is, “Does it progress?”, said one of the lead researchers. That may depend on what we eat.

“The question is not whether a certain diet allows you to do well in the short term”, one of the researchers noted, “but can it help you survive to be 100?” It wasn’t just more deaths from cancer. Middle-aged people who eat lots of protein from animal sources were found to be more susceptible to early death in general. Crucially, the same did not apply to plant proteins, like beans, and it wasn’t the fat, but the animal protein that appeared to be the culprit.

What was the response to the revelation that diets high in meat, eggs, and dairy could be as harmful to health as smoking? Well, one nutrition scientist replied that it was potentially dangerous. It could damage the effectiveness of important public health messages. Why? Well, a smoker might think, “Hey, why bother quitting smoking if my ham and cheese sandwich is just as bad for me?’”

It reminds me of a famous Philip Morris cigarette ad that tried to downplay the risks by saying, “Hey, you think secondhand smoke is bad, increasing the risk of lung cancer 19%; well, hey, drinking one or two glasses of milk every day may be three times as bad—62% increased risk of lung cancer. Or doubling the risk frequently cooking with oil; or tripling your risk of heart disease eating non-vegetarian; or multiplying your risk six-fold eating lots of meat and dairy.” So, they conclude, “Let’s keep some perspective here.” The risk of cancer from secondhand smoke may be well below that of other everyday activities; so, breathe deep. That’s like saying, yeah, don’t worry about getting stabbed, because getting shot is so much worse. It’s like saying if you don’t wear seat belts, might as well have unprotected sex. If you go bungee jumping, might as well disconnect your smoke alarms at home. Two risks don’t make a right.

Of course, you’ll note Philip Morris stopped throwing dairy under the bus once they purchased Kraft Foods.

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’s 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 just an approximation of the audio, contributed by Allyson Burnett.

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