Updated 13th March 2023

Fiber: Why it's important and how to get more of it

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    Diets rich in fiber are associated with good heart health and metabolic wellbeing. Plus, this type of diet can improve our gut microbiome.

    With so many benefits, relatively low cost, and high availability, fiber should be a staple nutrient in our diets — but most of us have a deficiency.

    In today’s short episode of ZOE Science & Nutrition, Jonathan and Will ask: If fiber is so good for us, why are we not eating enough of it?

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    If you want to uncover the right foods for your body, head to joinzoe.com/podcast and get 10% off your personalized nutrition program.

    Research referenced in today's episode

    Carbohydrate quality and human health: A series of systematic reviews and meta-analyses

    This podcast was produced by Fascinate Productions.


    [00:00:00] Jonathan Wolf: Hello and welcome to ZOE Shorts, the bite-sized podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolf, and this week I'm joined once again by board-certified gastroenterologist and ZOE's US medical director, Dr. Will Bulsiewicz, and today's subject is fiber. 

    [00:00:29] Will Bulsiewicz: This is a topic that I love talking about. It's one of my great passions. Fiber is one of the most misunderstood nutrients, and despite its potential health benefits, the majority of people in the United States and the UK, they don't have enough fiber in their diets.  

    [00:00:43] Jonathan Wolf: And I'm glad we could get the world's most passionate man about fiber onto this podcast Will 

    So, Why aren't people eating enough fiber?  

    [00:00:51] Will Bulsiewicz: Well, we think there's a clear answer to this question and there's also very solid research evidence to back it up.  

    [00:00:58] Jonathan Wolf: Fantastic. So let's get started and let's start with what is fiber?  

    [00:01:10] Will Bulsiewicz: This may shock people. Fiber is a type of carbohydrate that the body simply isn't able to digest. And most carbohydrates, they're broken down by the body and they're made into their pieces, which is glucose; sugar. People have heard about this. Fiber can't be broken down into sugar molecules and because of this, it passes through your body undigested. 

    And there are two main types of fiber that people need to know about. One is soluble fiber and the second is insoluble fiber. Soluble means that if you were to put it into a drink and stir it, it would dissolve.  

    [00:01:42] Jonathan Wolf: Makes sense, I guess that's why it's called soluble.  

    [00:01:45] Will Bulsiewicz: Yeah. It's implicit and it's nice when science the words make sense, so  

    [00:01:49] Jonathan Wolf: Doesn't always happen 

    [00:01:50] Will Bulsiewicz: Exactly. Research shows that soluble fiber can lower our glucose levels and our cholesterol, and there are a number of other health benefits that we'll talk about.  

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    [00:01:57] Jonathan Wolf: And so what kind of foods can we find fiber in?  

    [00:02:01] Will Bulsiewicz: Well, the good news, Jonathan, is that fiber is not hard to find. You can find fiber in plant foods. 

    I mean like literally. All plants contain fiber. So fruits, vegetables, whole grains, seeds, nuts, and legumes. And then there's one exception to this rule, which are mushrooms.

    Mushrooms technically are not plants, they're fungi, but they can also be a great source of dietary fiber. And I'm sort of nominating them to be honorary plants because I think they're great and they also can provide these same benefits that you find in plants. 

    [00:02:31] Jonathan Wolf: That's fantastic. My son often complains about all the plants that I want to give to him, and now I'm going to be like ah, eat the mushrooms. They're not even plants. So I'm going to use that now. Let's deal with maybe the elephant in the room when it comes to fiber. So I think a lot of people are listening to this and thinking, Yeah, but fiber is boring. 

    You know, it's that thing that you use to like regulate your bowel movements if you get constipated. And in fact, I remember back to, you know, when I was speaking to doctors 20, 25 years ago who were gastroenterologists and they told me, Fiber is roughage. I remember that word that helps you to go to the toilet more often. 

    And so I think for a lot of our audience, that's basically what they're thinking when they hear about this. Can you clear that up?  

    [00:03:17] Will Bulsiewicz: I get it. I understand where people are coming from. Fiber has a boring reputation. This is the stuff that grandma would stir into her drink so that she could have a bowel movement. 

    And so, you know, we associate dietary fiber with having bowel movements, but it's far more complicated than that. Simply consuming fiber in our diet can have massive health benefits, and it's so much more than your bowel movements. What traditionally has been thought of as being boring? 

    There is new science around fiber that has fiber sort of becoming this exciting new thing and there's a renaissance occurring around fiber.  

    [00:03:52] Jonathan Wolf: Well look Will before everyone switches off this podcast because they're like, 'Oh my God, I don't want to hear about fiber anymore, it's so boring.' Tell me about why this new science has you so excited. 

    [00:04:03] Will Bulsiewicz: Okay, I'm going to jump straight to my favorite fiber study of all time. This study had over 135 million person-years of data. Think about that, Jonathan, like humans have only been on the planet for 3 million years.  

    [00:04:17] Jonathan Wolf: That's an amazing amount of data.  

    [00:04:18] Will Bulsiewicz: Yeah, and it's great because it is taken the bias outta the equation. 

    Like, let's not just cherry-pick the study that tells us what we want to hear. Let's look at the whole picture.

    So here's what they found. When people increase their dietary fiber, they reduced the likelihood that they will be diagnosed with heart disease, and several types of cancer, they are less likely to have a stroke, and they're less likely to be diagnosed with diabetes. 

    And then the 58 randomized control trials. In these studies, they found that people who consumed more dietary fiber lost weight, lowered their blood pressure, and lowered their cholesterol. These are risk factors for heart disease. So ultimately what we're talking about is that we can reduce our exposure to four of the top 10 causes of death in our countries by simply eating this boring nutrient. 

    [00:05:02] Jonathan Wolf: This is pretty amazing, right? You know, there are all these arguments about like, which milk to use to go with your cereal, where we discuss this on a recent podcast and Sarah was explaining, the health impact of this is, is unknown. There's no data to show the differences. And yet here the data on how fiber can extend your life is incredibly strong. So I think that is striking. Just to stop for a minute and think about that.  

    Now, beyond that, what about other benefits of fiber? And I think there's common thought probably also with many of our listeners, that if you eat more fiber, you're gonna feel fuller for longer. Now, is that true or is this just another food myth? 

    [00:05:43] Will Bulsiewicz: This is true. Fiber can affect many different aspects of our body, including our metabolic health, and it certainly can affect how full we feel after a meal. It also improves our blood sugar control. It helps to regulate our blood lipids, and it also affects our immune system.  

    [00:06:01] Jonathan Wolf: And what about the effect that fiber has on our gut microbe? 

    [00:06:04] Will Bulsiewicz: It's a powerful effect. Dietary fiber is unique because we as humans, lack the enzymes to digest fiber, but that doesn't mean that it just goes through the body undigested. What that means is that fiber makes its way to the large intestine without changing, and when it arrives there, this is where the gut microbes, that's where they live. 

    It comes into contact with your gut microbiome who have tens of thousands of enzyme. Specifically designed to break down fiber. 

    [00:06:33] Jonathan Wolf: So we don't have them. You're saying so it passes through us, unlike bread or the oil or burger or whatever. We can break that down. But this fiber goes all the way through cuz we haven't got any of these. And then you're suddenly saying, Wow, in my gut I've got like 10,000 of these things that are sitting in my microbes waiting to break it up.  

    [00:06:53] Will Bulsiewicz: The number is 60,000. That's how many unique enzymes they think these microbes have. And take this, for example, I mean this is crazy. I am a very large human. I am six foot four, about two meters tall, and I weigh over 200 pounds, so about a hundred kilos. 

    Oh, less than a hundred kilos, and I don't have these enzymes, but a single cellular bacteria that is invisible to the naked eye could have hundreds of these enzymes. Mother Nature provides for us, but in a unique way where the gut microbes are supporting our body in a way that we're not able to do ourselves  

    [00:07:34] Jonathan Wolf: Well as someone who's a lot less than six foot four, I, I feel good about the idea that you know, just being big isn't always the optimal outcome Will.  

    [00:07:42] Will Bulsiewicz: Yeah, there's a, there are advantages and disadvantages, Jonathan, but nonetheless, you know, these microbes, they use these enzymes to transform the fiber and the fiber truly emerges as something different. 

    Which are called short-chain fatty acids. Perhaps people have heard of butyrate which is the classic short chain fatty acid. Butyrate ends up being this amazing anti-inflammatory molecule, which is the primary source of fuel in your colon. It supports good microbes. It directly suppresses the bad microbes. 

    It repairs the gut barriers. So like people wanna know, how do I fix leaky? I'm telling you right now. So this is why fiber is so good for our gut, and it's also why fiber is good for our entire body because these short-chain fatty acids don't just affect the colon. They spread throughout the entire body and they have healing effects everywhere they go. 

    [00:08:27] Jonathan Wolf: So it all sounds amazing. Will, are there any downsides to fiber?  

    [00:08:34] Will Bulsiewicz: I mean, of course, you know, we have to keep it real. So there are people who have digestive issues. that will struggle to process and digest fiber. That's just being honest and in that setting, they may experience gas and bloating and flatulence, and perhaps abdominal discomfort. 

    My message to these people, what I want you to know is that you're struggling with the digestion of fiber because your gut has been damaged. These microbes, they're struggling to keep up with what you're asking them to do. It's just important to understand these limitations because they can be overcome. 

    The benefits of fiber can be enjoyed by all. It's just that some of us need to work through a process to get there.  

    [00:09:14] Jonathan Wolf: And I know that this is quite a big topic, but if we kept it simple: what is that process? How would you approach this with a patient?  

    [00:09:22] Will Bulsiewicz: I would treat this like we're doing rehab for a bodily injury. So like pretend that you hurt your knee, Jonathan.

    You have choices on how you fix that problem, and one of them could be that you just stop walking permanently, but you would never do that because your knee would get weaker and so would the rest of your body. What you would do instead is that you would ultimately put yourself into a rehabilitation program where you challenge your knee ever so slightly, not aggressively. 

    By challenging your knee, it slowly gets stronger and you incrementally increase the challenge until the knee is completely back to healthy. That's actually what we need to do with our gut when it comes to dietary fiber. If you struggle with dietary fiber, don't eliminate fiber. Start low and go slow. 

    Reduce the amount of fiber intake that you have, and then slowly over time, increase it. And what you'll find is you're able to tolerate more.  

    [00:10:17] Jonathan Wolf: So does this mean It's as simple as saying the more fiber you eat, the better?  

    [00:10:23] Will Bulsiewicz: So generally, yes, but like all things in nutrition, Jonathan, we know that there is no one size fits all. 

    Fiber is a very broad term, describing many different types of fiber, so they're biochemically unique, and understanding how our body is gonna react to these unique forms of fiber is something that we are in the process of working through.  

    [00:10:48] Jonathan Wolf: And so fiber is so great. Why in fact, aren't we all just munching down on much more of it? 

    [00:10:54] Will Bulsiewicz: First I don't think most people have heard the exciting new science with fiber that talks about gut microbes and short chain fatty acids. I mean if you're using the outdated information, you think fiber is boring. While I'm sitting over here saying fiber is damn sexy.  

    [00:11:09] Jonathan Wolf: you have an interesting idea of what's sexy Will. I think we also have to keep it real. A lot of unhealthy food just tastes amazing. And that's not by chance, you know, if we are buying it from the store, it's probably being designed by some very smart nutritional scientists to just trigger the exact bliss point. It's also gonna give us probably like an immediate sugar rush. 

    So these things are incredibly tasty and again, I always look at my kids as soon as you start to open them up to these sorts of ultra-processed foods. They quite reasonably don't want to eat any of the healthy food you've given them before. And they're three, right? They're not thinking about anything other than what tastes best. 

    [00:11:49] Will Bulsiewicz: Yeah, no, that's true. I've experienced that with my kids as well. It's like Pandora's box, once they've had a taste, it's like if you bring it into the home, that's all they're going to want. So it can be quite challenging.

    Fiber-rich foods, sort of the way that I see it in terms of the benefit is they're the ones that have you feeling great for hours, but they don't necessarily give you that like punchy like, Hey man, I felt great for five minutes the way that you would with some of these ultra-processed foods. I don't really like it when my food leaves me feeling hung over. 

    [00:12:29] Jonathan Wolf: So Will, we covered a lot of ground here for a short, What's the conclusion is fiber that boring old nutrient? We don't like to think about it.  

    [00:12:37] Will Bulsiewicz: Fiber's exciting. Fiber is the new science that is unfolding. You know, it's quite amazing, Jonathan, when I dig into the medical literature, how often you will see fiber and short-chain fatty acids popping up in terms of being beneficial for our health. 

    [00:12:51] Jonathan Wolf: So given all of this, we did a little research about how much fiber we are all eating in the UK. The National Diet and Nutrition Survey says that Brits, on average consume 18 grams of fiber a day. Intake in the US is slightly less, 16 grams a day. So equally bad, given the recommended daily intake is 30 grams. So it's quite a shortfall Will. 

    [00:13:12] Will Bulsiewicz: Yeah, from my perspective, I consider this, a public health problem of the highest urgency. I mean, this is disturbing to me. But you know, the important thing that I want people to understand is that for those who are deficient in their fiber consumption, which frankly is most of us, they would improve their health by increasing their fiber consumption. 

    And that doesn't mean that there's any sort of hard rule of how fast you have to increase it or how high it needs to be. You simply need to wean into this process of slowly increasing your fiber intake and then your body can tolerate it. And also you're getting the health benefits that come from that. 

    [00:13:52] Jonathan Wolf: Amazing. I think that's a wonderful place to end today. If you've enjoyed today's podcast and you're curious about what high-fiber foods are best for you specifically, or if you just like to know more about your own body, do try ZOE's personalized nutrition program. You can get 10% off by going to joinzoe.com/podcast

    I'm Jonathan Wolf. 

    [00:14:11] Will Bulsiewicz: and I'm Will Bulsiewicz.  

    [00:14:13] Jonathan Wolf: Join us next week for another ZOE Podcast.

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