So what can we do to restore order and bring out the best in our ’biota? Where do we begin if we want to heal our guts to reverse or prevent illness? Is it probiotics? Bone broth?
Well, if you were sitting across from me in my office, I’d be going straight for my secret weapon—fiber. I know what you’re thinking. “Fiber? Really? Fiber is, like, the most boring thing on the entire planet, Dr. B,” or “You mean that gross white powder my grandma mixes into a glass of water every morning so she can poop?”
And to that I’d say: Fair enough. Fiber has gotten a bad rap, and those tasteless fiber supplements are only partly to blame. It’s also the fact that until very recently we had absolutely no idea just how amazing fiber is for your gut microbiota. You most likely have preconceived notions about it that make it hard for me to make fiber cool or sexy. For a while now, the diet conversation has been all about protein and, more recently, fat. Nobody has been talking about boring old fiber. I’m here to tell you that fiber is the first, and potentially the most powerful, solution to restoring health to your gut microbiota, and from there your overall health.
But for this to work I need you to unlearn what you think you already know. I’m not talking about fiber as you know it. It’s time for a reboot. A renaissance. A rebranding. It’s time to stop thinking about fiber as being vanilla and boring and get to know it in a whole new light. Fiber is so much more than you once thought it was. Yes, fiber is the real deal, folks. If by the end of this chapter you want to intentionally mispronounce it as “FIRE,” I don’t blame you. I’m going to resist that urge for this book, but if we ever meet in person I hope you’ll shake my hand and tell me the secret code, “Fiber is FIRE.”
Did you know that 97 percent of us consume an excess of protein, yet we still constantly ask, “Where am I going to get my protein from?” We live in a country with a pathologic protein obsession. Meanwhile, we are figuratively and literally starving for fiber. “Starving?” you say. “In this country? Where nearly three in four are overweight?” Absolutely. Your gut is completely FIBER STARVED. Imagine your gut as a dried-out, postapocalyptic wasteland, with a lone tumbleweed rolling through. That solitary tumbleweed represents your fiber! Less than 3 percent of Americans get even the recommended minimum daily intake. That means 97 percent of Americans are not receiving the minimal daily recommended amount of fiber, let alone what I would characterize as optimal. Of all of the essential nutrients, this may be our greatest, most prevalent deficiency. Yet, we’re not talking about it and no one seems to be concerned. Enough with the protein obsession; it’s time we turn our attention to the vital question: “Where am I going to get my fiber from?”
Okay, taking it from the top: What is fiber? In nature, fiber is a part of the plant cellular structure. Plants have a total monopoly on this nutrient. So if you want it, there’s only one way to naturally get it: from plants!
From a nutritional perspective, fiber is a carb—it’s what we would refer to as a complex carbohydrate. If you take multiple sugar molecules and link them together, you’d get fiber. That doesn’t mean it behaves like sugar by any means. It doesn’t. Digestion of refined sugar starts in the mouth and in about twenty minutes it’s already been absorbed in the small intestine. Meanwhile, fiber remains unblemished as it passes through your mouth, stomach, and even fifteen to twenty feet of small intestine so that by the time it reaches your colon, it’s the same molecule that went in your mouth.
Two of the biggest myths about fiber are that all fiber is the same and that it does nothing more than go in one end and shoot out the other like a torpedo. Let’s dig deeper.
You’ve been taught that all fiber is created equal—that whether it’s in your breakfast cereal, the milky powder your grandma drinks, or in a granola bar, all forms of fiber are interchangeable. All you need to do is count the number of grams and you’re good to go. What you’ve been told is dead wrong.
The source of the fiber you eat is critically important. The fiber in your cereal or breakfast biscuit is not the same as the fiber in your quinoa. This is conceptually similar to how the source of our fats and our protein determines the impact on our microbiome. It’s an oversimplification to reduce fiber to a number of grams and pretend that all grams are created equal. As you’re going to learn in Chapter 4, I have a much better way to source your fiber.
We’ve been taught to count grams of fiber for two reasons. One, it’s easy, and we like easy. And two, we have no clue how many types of fiber actually exist in nature. It’s incredibly difficult to analyze the chemical structure of dietary fiber, and there are four hundred thousand plants on our planet, three hundred thousand of them being edible. So there must be hundreds of thousands—if not millions—of types of fiber in nature. But we haven’t gotten around to figuring them all out yet.
Given the complexities in analyzing dietary fiber, we’ve simplified it by saying there are two basic forms of dietary fiber: soluble and insoluble. You can tell which is which by submerging the fiber in water. If it dissolves, it’s soluble. If it doesn’t, it’s insoluble. While I will occasionally make references to the difference between soluble and insoluble fiber, just know that in both cases we are talking about huge categories of fiber and that most plants contain some mix of both.
If you do a quick Google search on fiber, you’ll find the general health benefits of fiber: It contributes to fantastic bowel movements by correcting diarrhea and constipation and increasing the weight and size of your bowel movement, lowers cholesterol, and controls blood sugar. These are all great things, and we should be celebrating these health benefits of fiber, for sure! But at the same time we have been doing the undersell of the century here, folks.
We’ve all been taught that fiber pretty much goes in the mouth and out your . . . well, you know, and along the way it sweeps some stuff out. And while there may be some truth to these statements, we’re being excessively simple about an incredibly complicated nutrient. So let’s take a closer look.
We humans lack the ability to process fiber by ourselves. Sure, we’ve got some enzymes called glycoside hydrolases that help us break down complex carbs, but we only have seventeen of them—just seventeen!—and none of them are designed for breaking down the larger molecules like fiber. In other words, we big strong humans are literally incapable of processing fiber on our own.
Now, if we lived encapsulated in a sterile bubble free from bacteria, we would never know the true power of fiber. But we get by with a little help from our friends. Because guess where you can find lots and lots of fiber and complex carbohydrate-processing enzymes? Yes, in our gut microbiota. Compared to the shockingly inadequate seventeen that belong to us, our gut microbiota may contain upward of sixty thousand of these helpful enzymes.
The fact that our microbiomes contain this insane number of digestive enzymes makes sense when you remember that there are three hundred thousand edible plants and potentially millions of types of fiber in our diet. By outsourcing fiber digestion to our microbes, we are taking advantage of their adaptability. Every single plant, every single type of fiber requires a unique team of microbes working in concert to get the job done. It’s demanding work, but what follows is magic. The breakdown of fiber by gut bacteria unleashes what I believe is the most healing nutrient in all of nature: (*Drumroll, please!*) short-chain fatty acids (SCFAs).
We’ve learned about our “good bacteria.” But how do these powerful microbes actually do their incredible work? Good bacteria have the ability to transform certain types of fiber into electric, organic power manna—they’re called SCFAs.
There are three main types of SCFAs: acetate, propionate, and butyrate. These are literally as they are described: short-chain, meaning made up of two, three, or four carbon atoms connected together in acetate, propionate, and butyrate chemical compounds, respectively. The three SCFAs work in the body as a complementary group. In the interest of understanding them better we generally study them in isolation, but always keep in mind that there are studies and then there’s real life. In real life, these molecules are meant to work together, in the proper balance, for the good of your health.
Each type of fiber we consume produces a different mix of these SCFAs when processed by good bacteria. But don’t worry about trying to get specific ones for specific problems—the key here, which you’ll learn all about in Chapter 4, is to consume a diverse mix of fibers, meaning a diverse mix of plants, to get the benefits of all of them.
Before we go any further into the science of SCFAs I want to explain something. I’m sure you’ve heard of probiotics; we’ve all seen those yogurt commercials. Probiotics are all the rage and have been for some time. But have you ever heard of prebiotics or postbiotics? In short, probiotics are living bacteria that have been demonstrated to have beneficial qualities to us humans. Prebiotics induce the growth or beneficial qualities of the probiotics. They’re essentially food for the good bugs. Postbiotics are the healthy compounds produced by bacterial metabolism.
In other words:
Prebiotics = Food for healthy gut microbes
Probiotics = Microbes with beneficial qualities
Postbiotics = Compounds produced by gut microbes
Taken a step further . . .
Prebiotics + Probiotics = Postbiotics
The word “prebiotic” literally did not exist until 1995, but it is increasingly becoming a part of the American vernacular. It is defined as “a substrate that is selectively utilized by host microorganisms conferring a health benefit.” In other words, prebiotics (the substrate) are utilized by the microorganisms (probiotics) to confer a health benefit by producing postbiotics. Which is just the nerdy way of saying my formula: prebiotics + probiotics = postbiotics.
Not all fiber is prebiotic. Most soluble fiber is prebiotic, while most insoluble fiber is not. We often call insoluble fiber roughage. The roughage is the part that’s untouched by our digestion or our microbes, and therefore launches out the bottom like a torpedo.
Fiber isn’t the only prebiotic though! Resistant starch, found in foods like oats, rice, potatoes, and legumes, is technically not fiber but it behaves in a very similar way to soluble fiber. It passes through the small intestine unblemished and is fermented by our colon microbes. A mother’s breast milk also contains something called human milk oligosaccharides, or HMOs, that function like soluble fiber and feed the baby’s developing gut microbiota. So if we want postbiotic SCFAs, we should get prebiotic soluble fiber and resistant starch in our diet and we should breastfeed our young ones.
All roads point to SCFAs for human health. They are the dominant driver of gut health and they have benefits throughout the body.
Now let’s come back to SCFAs, your good gut bacteria, and fiber. Healthy bacteria can’t survive without fiber. In fact, studies have shown that fiber consumption increases the growth of healthy bacteria species such as Lactobacilli, Bifidobacteria, and Prevotella. Eating fiber also increases the diversity of species within the gut. These beneficial effects are what qualify it as a prebiotic. The prebiotic effects of fiber feed and nourish the healthy microbes in our gut. Your gut bacteria goes from slumped over and worn out to energized, steadfast, and powerful.
Those reinvigorated microbes release SCFAs from fiber to heal the colon. First, the short-chain fatty acids do as their name suggests and make the colon more acidic. This change prevents the growth of inflammatory, pathogenic bacteria—the bad guys. Next, SCFAs take it a step further and directly suppress dangerous strains like E. coli and Salmonella. In Chapter 1 we learned that dysbiosis is characterized by a loss of balance between the healthy microbes and the inflammatory ones. By suppressing inflammatory microbes, SCFAs are helping to restore that balance.
Now we’re building momentum toward a healthier gut. Fiber is feeding the healthy microbes, and they’re multiplying. As they increase in number, they’re producing more and more SCFAs for us even though you’re consuming the same amount of fiber. You have trained your gut to produce SCFAs, and it’s become increasingly efficient at doing that. These SCFAs are suppressing the inflammatory microbes, giving the healthy microbes an even more decisive advantage over the inflammatory ones. This is a form of positive health momentum, and it starts building on itself as we get more and more healthy microbes producing more and more SCFAs. But keep in mind, the linchpin here is fiber. Everything I’ve described is contingent on fueling your gut microbes with prebiotic fiber.
As you can see, regular consumption of fiber trains your gut microbiome not only to process fiber, but to actually get even more beneficial postbiotics out of it! In exercise we call it muscle memory. In life we call it practice. Either way, our microbes are no different. If you regularly expose them to fiber in your diet, they will adapt to that regular exposure and get really, really good at extracting SCFAs for you. With that comes a myriad of benefits that I’m just starting to tell you about.
But here’s the problem—the flip side is also true: a diet lacking in fiber will drain your gut of its fiber-extracting capabilities and make it less capable of getting postbiotics from your food. When you don’t practice, you lose your skill, right? Just two weeks on a low-fiber diet causes an altered gut microbiota that starts to literally eat away at the intestinal lining, causing breakdown of the protective barrier and susceptibility to disease. Not good. And remember how I said that 97 percent of us aren’t even getting minimal fiber? And that six of the top ten causes of death in the United States are caused by nutrition? And that most of those are linked with dysbiosis of the gut? You’re starting to get the FIRE for fiber burning a little now, aren’t you?
This is a really key point that I want to get across. You can call it nutritional karma—“do good and you will receive good.” Or you could say that you’re not what you eat but what your gut microbiota eats. The point is that your food choices leave an imprint in your microbiome and those choices will either train your gut bacteria to take care of and protect you or empower evildoers to hurt you. Your choice.
What else can SCFAs do? Well, they also fix up your colonocytes, which are the cells lining your colon. Maybe you’ve been led to believe that fiber provides no energy since it’s not absorbed? Believe it or not, 10 percent of our daily caloric requirements are met with fiber-derived SCFAs as the energy source. In fact, the main source of energy for our colonocytes are SCFAs, providing up to 70 percent of their energy. Specifically, the colonocytes seem to love chowing down on the SCFA butyrate, so most of the butyrate is taken up by the gut lining where it contributes to a healthy colon. Like taking a beautiful historic home that’s been run haggard and restoring it to its original glory, butyrate fixes up the lining of the gut.
Back in Chapter 1 we talked about dysbiosis, which is when damage to the gut microbiota causes increased intestinal permeability, which leads to release of noxious bacterial endotoxin. Remember that the gut wall is meant to act like a physical barrier exerting control over what stuff gets access to your blood. After all, it’s in the gut that your body is most exposed to the outside world. This blood–gut barrier is meant for protection, but holes can occur in the wall allowing bacteria, antigens, and toxic substances like bacterial endotoxin to get past the intestinal wall, activating the immune system. This increased intestinal permeability, which some refer to as “leaky gut,” happens when tight junction proteins that are meant to keep cells connected to one another end up being broken, thereby creating gaps between the cells. Good news: SCFA butyrate actually repairs leaky gut by increasing the expression of tight junction proteins and has been shown to actually decrease endotoxin release.
And while we’re on the topic, inflammation caused by increased intestinal permeability affects the function of the intestinal lining, including its nerves and muscles. This leads to diarrhea or constipation, bloating, and abdominal pain. Unfortunately, even just transient inflammation of the gut and intestinal hyperpermeability can cause sensitization and altered motility that persists long after resolution of the inflammation. You may recall from Chapter 1 that the hallmarks of irritable bowel syndrome are altered gut motility and increased visceral hypersensitivity. SCFA butyrate has been shown to increase colonic motility and decrease visceral hypersensitivity. So if you suffer from IBS, then you want this.
Let’s take a step back for a moment here, folks. What I’m telling you is that SCFAs are a vital nutrient for intestinal health. They are the dominant energy source for your colon, support a healthy gut microbiota, repair leaky gut, reduce release of bacterial endotoxin, promote intestinal motility, and decrease visceral hypersensitivity. Read that sentence again: Let it sink in. I just described the cure for dysbiosis. I believe that dysbiosis is at the root of most modern disease. SCFAs can correct dysbiosis, and that’s only the beginning of the health benefits they offer.
If correcting dysbiosis, supporting a healthy gut microbiota, repairing your colon, and reversing leaky gut weren’t enough, this superhero energy fans out throughout the body and works its healing magic. Let’s take a look at some of the most impressive capabilities of SCFAs beyond the gut.
Just beyond the wall of your intestine sits 70 percent of your immune system. This is your little army. When infection or even cancerous cells arise, it is the responsibility of your immune system to clear it out. Sounds simple, but it’s not. How do you separate friend from foe when there are thirty-nine trillion microbes in the gut, thirty trillion human cells in the body, and your “host” is scarfing down three pounds of food per day, most of which is some deviant form of real food? That’s a ton of responsibility. The slightest bit of confusion by the immune system leads to failure. Overreact and you get allergic or autoimmune issues. Underreact and you get infections or even cancer. So how do we get it juuuussssstttttt right?
Well, SCFAs are the way that our gut microbiome connects to our immune system. It’s how they communicate with each other. SCFAs act as a crisis negotiator, getting the immune system to cool off if it’s too hot.
Dysbiosis and the release of bacterial endotoxin promote inflammation, which is a good thing when you have an infection or injury but isn’t good when it’s constant and unneeded. It’s unrelenting low-grade stress on the body, including the immune system. Thankfully, SCFAs address both dysbiosis and bacterial endotoxin release, which makes them a great first step toward regulating the root cause of all inflammatory conditions.
Beyond that, SCFAs have been shown to inhibit three of the most powerful inflammatory signals in the body: NF-κΒ, IFN-y, and TNF-α. I’ve heard people say that “your genes load the gun and your lifestyle pulls the trigger.” If that’s the case, then SCFAs disarm the gun and take it out of your hand. SCFAs make immune cells more tolerant to gut bacteria and reduce gut inflammatory markers. Believe it or not, they even make immune cells more tolerant to your food, helping to prevent food allergy and sensitivity. SCFAs can even communicate directly to an important part of our immune system called regulatory T cells, which you can think of as “suppressor” cells that cool off the immune system, encourage tolerance to your own cells, and prevent autoimmune disease. More on that in a bit.
We’ve seen more evidence of the power of fiber fueled SCFAs against inflammation in studying patients with Crohn’s disease, a form of inflammatory bowel disease (IBD). In Crohn’s, the immune system attacks the intestine, causing inflammation. It can affect any part of the digestive tract, from your lips to your backside. The inflammation in Crohn’s can be so severe that it can actually erode through the wall of the intestine and cause abscesses or a connection between two parts that isn’t supposed to exist, which we call a fistula. Suffice it to say that Crohn’s is a horrible, debilitating condition that is becoming increasingly common in the Western world.
So let’s take a look at how Crohn’s disease develops and you’ll see how SCFAs could make a difference. In people with Crohn’s, we see decreased bacterial diversity, loss of butyrate-producing organisms, specifically Faecalibacterium prausnitzii, and an overgrowth of pathogenic bacteria, specifically E. coli. But this isn’t just any E. coli. . . . No, no, no. This is an extra-nasty variety called adherent-invasive E. coli. Gives me the chills typing it, that’s how nasty it is. Anyway, this E. coli behaves like a sociopath just broken out of prison, and immediately starts unleashing pro-inflammatory proteins like a flamethrower as it proliferates, further enhancing dysbiosis and the rise of more E. coli. This loss of balance in the gut, decrease in good bacteria, and increase in E. coli affects the tight junctions and leads to increased intestinal permeability. There is a strong association between depletion of F. prausnitzii and the immune system no longer being tolerant of the intestinal microbiota, meaning the immune system starts going haywire. Meanwhile, the absent intestinal barrier allows E. coli to invade the intestinal wall, which activates the immune system to attack the E. coli. And there you have it—inflammatory bowel disease.
As you can see, just like in life, when bad things happen in the body it’s a series of events that lead to the problem. If we were functioning in the business world, we’d do a root cause analysis to figure out the source of the problem and address it. Could a fiber-starved gut be the root cause of Crohn’s disease?
Well, yes: SCFAs are relevant in protection from Crohn’s disease on a mechanistic level because they make immune cells more tolerant to gut bacteria, help suppress an overactive immune system, repair leaky gut, and create protective bacteria to keep the gut healthy. Additionally, in a recent study a semi-vegetarian high-fiber diet basically crushed an omnivorous diet in terms of keeping people with Crohn’s disease free of disease activity and in remission. Those on a semi-vegetarian diet maintained a 92 percent remission rate compared to just 33 percent among omnivores in a prospective trial.
And in similar fashion, what if a high-fiber, plant-centered diet proved to be beneficial for other autoimmune, inflammatory conditions? Well, it does. In humans, a vegan diet has repeatedly been demonstrated to be beneficial for disease remission in rheumatoid arthritis. For example, in a randomized controlled trial 41 percent of patients on a vegan diet showed clinical improvement of their rheumatoid arthritis compared to just 4 percent on a “well-balanced” non-vegan diet.
So not only do SCFAs correct dysbiosis and heal leaky gut, but they also create a powerful link between the microbiome and immune system that serves to make the immune system work properly. Adequately fueled by SCFAs, the immune system does its job confidently and effectively. Without the SCFAs, the immune system becomes insecure, confused, paranoid, and weak. In other words, the immune system is dependent on gut microbes to support it with SCFAs. The gut microbes are dependent on you to offer fiber fuel that can be transformed into SCFAs. Again, these gut microbes aren’t just passively along for the ride. They play an active, central role in our health.
As we’ve learned, SCFAs correct dysbiosis, fix leaky gut, reverse bacterial endotoxemia, and optimize the immune system. Those effects create a good foundation for the prevention of cancer. We know from Chapter 1 that dysbiosis has been associated with several types of cancer: colorectal, gastric, esophageal, pancreatic, laryngeal, gallbladder, and even breast cancer. But is there anything special about SCFAs that can help us in the fight against cancer beyond just “healing the gut”?
Let’s start with the basic premise that cancer development requires unchecked cell multiplication and growth. In order for this to happen, the DNA in the malignant cell needs to be able to copy itself before dividing into two cells. Histone deacetylases, or HDACs, are required to allow this process to occur. So if you could shut down the DNA copy process by blocking the HDACs, you’d effectively be pulling the emergency brake on the runaway cancer train.
Since the 1970s we’ve known that butyrate inhibits HDACs, altering gene expression in malignant cells and, as a result, inhibiting the root of cancer formation—unchecked proliferation. But when you have dangerous cells that you’re dealing with, it’s not enough to just slow down their growth. You need to stop them in their tracks, and the way this is done is by causing apoptosis, or programmed cell death. Sounds violent, but it’s actually a normal part of cellular regulation and is by no means rare. Every day between fifty and seventy billion cells fall on the sword in altruistic fashion to protect the greater good of the whole organism. SCFAs help us in the fight against cancer by specifically eliminating cells that could turn into cancer.
Once again, studies on people who consume a high-fiber, plant-centered diet and reduce their cancer risk offer proof that these principles really translate to our real life. Let’s go straight to the source and start with the most powerful, most well-respected study on the topic by Dr. Andrew Reynolds in The Lancet. He pulled information together from 243 prospective studies. This is a scale that is rarely seen in clinical research, yet at the same time he restricted his data to high-quality studies: prospective cohorts and interventional randomized trials. In the end, fiber found in whole foods was shown to protect against colorectal, breast, and esophageal cancer. Further, high dietary fiber in the study was still pretty low—between 25 and 29 grams per day. In the Western world, our fiber consumption is so poor that even the high-fiber consumers are below goal. Nonetheless, the results suggested that as you extend your dietary fiber intake higher, the protection against colorectal and breast cancer only gets greater.
Colon cancer is the number two cause of cancer death in the United States right now. Number two! And that’s despite billions of dollars spent on our colon cancer screening program. Dietary fiber has been repeatedly shown to protect us from colon cancer. For example, in a prospective study of 1,575 people with nonmetastatic colorectal cancer, consuming more dietary fiber helped people live longer. For every 5 grams of increased fiber consumption, there was an 18 percent lower risk of death from colorectal cancer and 14 percent lower risk of death from any cause during follow-up.
And just to put the cherry on top, three major studies—a large 2017 meta-analysis, the prospective EPIC-Oxford study, and the Adventist Health Study—all reached the same conclusion when it comes to diet and cancer risk. A plant-centered, fiber fueled diet lowers your risk of developing cancer. Mic drop.
So SCFAs and fiber offer protection from cancer, the number two cause of death in the United States. How about heart disease and stroke—the number one and number five causes of death? In the same mega meta-analysis on dietary fiber published in The Lancet, Dr. Reynolds and his science squad also found dietary fiber consumption to be associated with lower body weight, reduced incidence of type 2 diabetes, lower total cholesterol, and lower systolic blood pressure. These just so happen to be the risk factors for coronary artery disease and stroke.
SCFAs affect multiple tissues in a concerted action to improve blood sugar regulation. They help protect against glucose intolerance, improve insulin response in the pancreas, and suppress fatty acids in the liver and peripheral tissues. This isn’t exactly a revolutionary concept. There are studies dating back to the 1980s suggesting that soluble fiber is protective against type 2 diabetes. But modern studies, such as the recent Science article by Dr. Liping Zhao, dug more deeply and have shown us that following a high-fiber diet promotes the growth of SCFA-producing microbes that improve blood sugar regulation.
It’s not just what you eat but the effect it has on your microbiota that determines your diabetes risk. There’s something that was originally called the “lentil effect,” but now we call it the “second meal effect,” that illustrates this idea. If you give two people an amount of bread or lentils for lunch that have the same number of calories, you will of course see less of a sugar spike with the lentils. No surprise. But then these two people both have white bread for dinner, you’ll still see less of a sugar spike in the person who had lentils for lunch. Same meal at dinner, but different effects based upon what you ate for lunch. We now understand that this happens because the bacteria that we empowered at lunch are working their SCFA magic to protect us at dinner. Score one for legumes, if you’re keeping track.
SCFAs also lower cholesterol by having direct control over the critical enzyme in cholesterol formation and by increasing excretion of cholesterol in bile. Further, SCFAs directly activate a receptor in fat cells that decreases fatty acid uptake, and therefore suppresses fat accumulation.
Each of these mechanisms protects you from obesity. Additionally, SCFAs promote the release of satiety hormones that tell you when you’ve had enough. This is a wildly underrated benefit that we are sacrificing with our current highly processed, low-fiber diet. It allows you to feel nice and adequately full without crossing the line to where you need a pair of sweatpants, a three-hour nap, and an energy drink to get your day back on track. (Not that there’s anything wrong with sweatpants!) When you are eating real food, nature works the way it’s supposed to and you simply stop eating at the right time without counting calories and without overeating. As proof of concept, a randomized crossover study recently showed people experienced greater satiety and increased satiety hormones after eating a plant-based burger with tofu than after eating a pork and cheese burger, even though the two meals were matched for energy and macronutrients. Same number of calories, same macros, but better appetite control with the plants. Shocking, right?
Finally, patients with symptomatic coronary artery disease have been found to have depleted levels of butyrate-producing gut bacteria. In animal models SCFAs have been shown to protect against congestive heart failure and high blood pressure. More recently they’ve also been shown to prevent atherosclerosis by maintaining gut barrier function and limiting bacterial endotoxin release, which leads to less vascular inflammation. A recent study in humans with congestive heart failure found an absence of SCFA-producing microbes and an increase in TMAO-producing microbes. These patients had less butyrate and more TMAO coursing through their blood. And so we now understand at least in part why a plant-centered diet is good for the heart. SCFAs are the antithesis of TMAO.
Like a Roman warrior throwing a spear, the superhero bacteria in our gut also unleash SCFAs all the way upstairs to the brain. What’s interesting is that many molecules cannot travel to the brain due to a wall of protection called the blood–brain barrier. Most molecules are stopped there at the wall, like being stopped at the VIP line at the most exclusive club in New York City. (I wouldn’t know what that’s like because I’m a nerd and have never been, but I watched enough Entourage to at least be able to pretend.) So imagine that when the SCFAs show up, the velvet rope is withdrawn and they’re given free access to the hottest club, our most precious organ, the brain.
On the other side of that velvet rope, SCFAs continue to work their magic. The same chemical that reverses dysbiosis, heals leaky gut, strengthens the gut microbiota, optimizes the immune system, and regulates appetite and metabolism also connects the gut microbiome to cerebral function. The effects are once again broad and powerful.
You know how many people with leaky gut also complain of brain fog? And how we also discussed above that SCFAs can activate tight junction proteins to repair increased permeability in the gut? Well, it appears that SCFAs work similar magic on the blood–brain barrier.
SCFA butyrate has demonstrated a profound effect on improving learning and memory. This has been demonstrated in models of Alzheimer’s, heavy metal toxicity, traumatic brain injury, and even neurologic infections (which sounds terrifying). I will tell you firsthand that the mental clarity that I’ve had since changing my diet has been life changing for me. Being totally real, there’s no way I could’ve written this book before. I didn’t have the stamina, focus, or neural plasticity.
Speaking of Alzheimer’s, one of the hallmarks of Alzheimer’s disease is the accumulation of amyloid plaques between nerve cells in the brain. Researchers are currently working on treatments for Alzheimer’s to block the production of amyloid. Millions if not billions of dollars are being spent on this. While they continue that quest, I want you to know that laboratory studies suggest that SCFAs interfere with the formation of this exact same amyloid.
Laboratory studies also show that butyrate protects the brain in models of Parkinson’s disease. This is quite interesting when you consider that human studies have found that patients with Parkinson’s disease have lower levels of the bacteria that produce SCFAs and, as expected, lower levels of SCFAs in their stool. For what it’s worth, Parkinson’s disease patients almost all have digestive issues, with constipation being the most common among them.
Finally, children on a high-fiber diet demonstrate better cognitive control (multitasking, working memory, and maintaining focus) than children who eat a lower-fiber diet. So SCFAs may help ADHD. I’d far rather kids eat a salad than take Ritalin.
Dr. Justin Sonnenburg showed that Westernization has led to a loss of gut microbial diversity in his study that compares the Hadza of Tanzania to Americans. The Hadza are one of the last remaining hunter-gatherer societies on the planet and provide insights into what our life and our microbiome may have looked like in primitive times. They consume 100 or more grams of fiber a day in their food, and during a year will include around six hundred plants in their diet. The average American gets a pathetic 15 grams of fiber per day and has fifty or fewer species of plants in their diet. The differences in the microbiota are profound. The Hadza have about 40 percent more diversity than the average American and about 30 percent more diversity than the average Brit.
Consider that African Americans have sixty-five times more colon cancer than rural Africans. Sixty-five times! One interesting study involved switching the diets of a group of African Americans and native Africans for two weeks. The Africans did a high-fat, low-fiber diet while the African Americans did a high-fiber, low-fat diet. Do you want to guess what happened?
When the native Africans began eating our American diet, they saw their SCFA butyrate levels decline and their TMAO levels increase. The reciprocal effect ended up being true for the African Americans. “Africanization” of the diet increased butyrate by 2.5-fold while “Westernization” cut butyrate quantities in half. Remember how secondary bile salts are known to cause colon cancer? A typical African diet reduced colonic secondary bile acids by 70 percent, while the Western diet increased them by 400 percent.
One last little mind-blowing nugget I want to leave you with: Dr. Sonnenburg also did a mouse study showing that the Western diet induced loss of microbial diversity that could be compounded over a series of generations. If your grandmother had twelve hundred species of microbes in her gut as a child, but by the time your mother was born she had nine hundred, that’s what your mother got. Then if your mother loses three hundred species, now you start off at six hundred—half of what your grandmother had. Perhaps it comes as no surprise in this study, the main factor that protected against this generational loss of diversity was adequate prebiotic fiber consumption. Granted, this is just an animal study. But it’s impossible to re-create in humans and it really makes sense.
The benefits of postbiotic SCFAs may seem a little too good to be true, but the science is real. SCFAs aren’t just important, they’re absolutely vital to gut health. They offer a solution to dysbiosis by correcting leaky gut and reducing bacterial endotoxemia. They feed and empower the healthy microbes in your gut so they can do their job! They also play a role in human health throughout the entire body. They offer protection from the most deadly diseases in the United States. That by itself should make it the talk of the town, the focus of our national conversation in our quest to better health. Yet this superstar languishes in anonymity. It’s time to change that. I’m building a fiber bandwagon. Who’s coming with me? Invite your friends. Grab your family. Let’s be loud and proud so they can hear us. It’s time for us all to be Fiber Fueled.
To view the 65+ scientific references cited in this chapter, please visit me online at www.theplantfedgut.com/research/.