Fiber: Why it’s important and how to get more of it
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Hello, and welcome to Zoë Shorts, the Bite Size 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 Zoë's US medical director, Dr. Will Bulsiewicz. And today's subject is fiber.

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. 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?

Well, we think there's a clear answer to this question and there's also very solid research evidence to back it up. Fantastic. So let's get started.

And let's start with what is fiber? 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 all the way through your body undigested.

And there's 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. Makes sense. I guess that's why it's called soluble. Yeah, it's implicit, and it's nice when science actually, the words make sense. So... Doesn't always happen. Exactly. Research shows that soluble fiber can lower our glucose levels and our cholesterol, and there's a number of other health benefits that we'll talk about. And

And so what kind of foods can we find fiber in? Well, the good news, Jonathan, is that fiber really is not hard to find. You can find fiber in plant foods. I mean, literally all plants contain fiber. So fruits, vegetables, whole grains, seeds, nuts, 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. That's fantastic. My son often complains about all the plants that I want to give to him. And now I'm really like, oh, 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 really boring. It's that thing that you use to regulate your bowel movements if you get constipated. And in fact, I remember back to when I was speaking to doctors 20, 25 years ago who were gastroenterologists and they told me, look,

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? I totally 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 actually far more complicated than that.

Simply consuming fiber in our diet can actually 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.

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, in fact, this new science has you so excited. Okay, I'm going to jump straight to my favorite fiber study of all time. This study had over 135 scientists

million person years of data. Think about that, Jonathan. Humans have only been on the planet for 3 million years. That's an amazing amount of data. Yeah. And it's great because it's taken the bias out of the equation. 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 reduce the likelihood that they will be diagnosed with heart disease, 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 controlled trials in these studies, they found that people who consumed more dietary fiber lost weight, lowered their blood pressure, 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.

This is pretty amazing, right? There are all these arguments about which milk to use to go with your cereal, where we discussed this on a recent podcast and Sarah was explaining the health impact of this is unknown. There's really no data to show the differences. And yet here the data on how fiber can actually extend your life is incredibly strong. So I think that is really 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 going to feel fuller for longer. Now, is that true or is this just another food myth? No, 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 has an effect on our immune system. And what about the effect that fiber has on our gut microbes? It's a powerful effect. Dietary fiber is unique because we as humans, we lack the enzymes to digest fiber, but that doesn't mean that it actually 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 literally tens of thousands of enzymes

specifically designed to break down fiber. 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 because 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 micros waiting to break it up.

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, so about two meters tall, and I weigh over 200 pounds, so about 100 kilos, a little less than 100 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. So this is mother nature provides for us, but in a unique way where the gut microbes are basically supporting our body in a way that we're not able to do ourselves. Well, as someone who's a lot less than six foot four, I feel good about the idea that just being really big isn't always the optimal outcome, Will. Yeah, yeah, yeah. There's advantages and disadvantages, Jonathan, but-

Nonetheless, these microbes, they use these enzymes to transform the fiber. The fiber truly emerges as something different, which are called short-chain fatty acids. Perhaps people have heard of butyrate as 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 the good microbes. It actually directly suppresses the bad microbes. It repairs the gut barrier. People want to know, how do I fix leaky gut?

I'm telling you right now. So this is why fiber is so good for our gut. And it's also why fiber is actually good for our entire body because these short chain fatty acids don't just affect the colon. They actually spread throughout the entire body and they have healing effects everywhere they go. So all sounds amazing. Well, are there any downsides to fiber? I mean, of course, you know, we have to keep it real. So there are people who have digestive issues and

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.

So 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. And I know that this is quite a big topic, but if we kept it really simple, you know, what is that process? How would you approach this with a patient? I would treat this like we're doing rehab for a bodily injury. So like pretend that you hurt your knee, Jonathan.

you know 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 like not aggressively

And 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 the time, increase it. And what you'll find is you're able to tolerate more. So does this mean it's as simple as saying the more fiber you eat, the better?

Uh, 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 like how our body is going to react to these unique forms of fiber is something that we are in the process of sort of working through.

And so fiber is so great, why in fact aren't we all just munching down on much more of it? At 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. If you're using the outdated information,

You think fiber is boring while I'm sitting over here basically saying fiber is damn sexy. You have an interesting idea of what sexy will. I think we also have to keep it real, right? A lot of unhealthy food just tastes amazing and that's not by chance. You know, if we're 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 going to 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. Yeah, no, that's really 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, right?

But they don't necessarily give you that punchy, like, hey, man, I felt great for five minutes, the way that you would with some of these ultra processed foods. Personally, I don't really like when my food leaves me feeling hung over. So, Will, we've 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?

Fiber is 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.

So given all of this, we did a little research about how much fiber we actually 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 at 16 grams a day. So equally bad given the recommended daily intake is 30 grams. So it's quite a shortfall, Will. Yeah. I mean, from my perspective, I consider this a...

public health problem of the highest urgency. I mean, this is disturbing to me. But 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 really improve their health by increasing their fiber consumption.

And that doesn't mean that there's any sort of hard rule of like how fast you have to increase it or how high it needs to be. You simply need to lean 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. 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 slash podcast. I'm Jonathan Wolf. And I'm Will Borsowitz. Join us next week for another Zoe podcast.