Gut health supplements may be big business, but what your microbiome craves most of all is good, old-fashioned fiber. It's time to give it the attention it deserves.
If ever there was a nutrient in need of a PR relaunch, it’s dietary fiber. Most Americans don’t even get half of the daily recommended intake of fiber, and yet we never seem to talk about it. That’s not because there’s any question about its importance – we know more about the vital work done by fiber, and the gut microbiome it helps, than ever before. It’s because it has an image problem dating back to the 1980s: the era of all-bran muffins and Grape Nuts, of ‘roughage’ and ‘keeping regular’. Fiber got slotted in the old-person’s aisle, with the canned prunes, and forgotten.
In the last decade, we’ve all got more clued up on the benefits of maintaining a healthy microbiome - the colony of friendly bacteria that live inside our bodies. A procession of miracle foods and supplements have been touted as THE secret to a healthy gut. Probiotics, prebiotics, ferments, cultures: we're feeding our gut flora a pretty expensive diet these days. Now that we all know our kombucha from our acidophilus, it’s high time for a reassessment of fiber as one of the key elements in any healthy diet. This is no passing fad: it’s a timeless classic that should never have been allowed to go out of fashion. And while studies show that two thirds of Americans think they eat enough fiber, only one in twenty of us actually does.
What's a "gut biome?"
That took guts. It was a gutsy move. I can feel it in my gut. We have long referred to the innate genius and, yes, bravery of our gastrointestinal tract (GI), even if we didn’t really understand why. These days we know more about the real work done by the genius gut. More than just a hollow transit system for food, the gut is an entire living ecosystem, home to a ‘microbiome’ or collection of microorganisms that aid in digestion and a lot more. The gut microbiome is the ecology of fungi, bacteria and other microscopic entities that interact with our GI tract to affect everything from our immune function to our sleep to, yes, regularity. And one of the few things this universe of gut flora asks for in return is fiber.
Is all fiber the same?
You might have an instinctive idea of what fiber is - the rough, chewy side of grains, fruits and vegetables, from bran cereal and potato skins to crunchy carrots and berries (with the seeds). But when we talk about dietary fiber, we’re giving a single, simple name to a wide range of chemical compounds found in our food. What they have in common is that these compounds - they’re called carbohydrate polymers - are complex enough that humans’ digestive systems can’t completely break them down.
The polymers that make up dietary fibers come in many forms, like cellulose and hemicellulose, pectins and mucilage. But the important distinction is between soluble and insoluble fibers, and both have different sets of benefits to our bodies. Soluble fibers are partially digested into a gel-like substance, feeding the gut flora and helping to lubricate the digestive tract. These fibers, known as beta glucans, also play a significant role in reducing cholesterol levels. Insoluble fibers pass through all the way, adding bulk to stool and making things run more smoothly. Each kind is important in a healthy diet.
What does fiber do?
Most nutrients in your food are dissolved and absorbed in your GI tract, thanks to a combination of rhythmic muscular contractions and digestive juices. Dietary fiber isn’t as susceptible to these processes, and stays largely intact all the way to the colon, where it lands right in the middle of that all-important microbiome. You may not be able to absorb it, but the helpful bacteria that live in your colon think intact fiber is yummy: they feast, and flourish. These bacteria are hard working and short-lived - you go through generations of them every day - and it’s important to provide a steady, plentiful supply of the fibers that help your gut allies thrive, called ‘prebiotic’ fibers.
Nurturing a large and diverse microbiome has been directly tied not just to better digestion, but to a more robust immune system, lower levels of inflammation throughout the body and even lower levels of food allergy. The gut microbiome communicates with your immune system to help the body fight infection, and may contribute to balancing everything from your weight to brain and heart function.
But fiber isn’t just about the microbiome. Its other crucial job is to eliminate excess cholesterol from the body. It does this both by “soaking up” cholesterol and fats in the small intestine, and by reducing the reabsorption of bile salts so that the body has to use cholesterol to make more. The benefits go on and on: Eating a fiber-rich diet also helps balance absorption of sugars, improving blood sugar levels and reducing the risk of type 2 diabetes. It enhances feelings of satiety (fullness) at meal times, which can help you recognize when you’ve had enough to eat. It can help control blood pressure, and even reduce the risk of some types of cancer.
How much fiber should I be consuming?
We humans used to really get fiber: archaeologists and anthropologists have shown time and time again that humans living in pre-industrial societies consumed enormously more of the stuff than we do now. So while many Americans lag behind at around 15g of dietary fiber each day, some historical and prehistoric peoples are known to have eaten more than six times as much: well over 100g each day. But don’t take this as encouragement to scarf down a quarter-pound of bran right away – too much fiber, especially when you’re used to small amounts, can lead to gas, bloating and generally awful feelings.
Instead, increase your intake slowly over time with a goal of 25-30g per day from grains, fruits and vegetables. (Not fiber supplements – your body needs diversity, which means prioritizing real foods.) And please make sure you assist the passage of this extra fiber by drinking plenty of water. High fiber coupled with insufficient water can create what we’ll politely call a log jam in your digestive system!
Where can I find fiber?
Fiber is only found in plants, and the best sources are whole foods.
Legumes are an easy shortcut – a cup of cooked black beans or lentils will get you at least halfway to your daily target.
Similarly, grains such as barley, oats and the so-called ‘ancient grains’ (spelt, millet, quinoa etc.) are famously high in fiber, and particularly rich in beta-glucans, the soluble fibers responsible for cholesterol reduction.
Switching from refined to whole grains - think oats, brown rice, whole wheat bread, bran cereals, and legume or whole-wheat pasta - is going to make a huge difference to your fiber intake. Seeds (pumpkin, sunflower) nuts (walnut, almond) and popcorn make great fiber-rich snacks.
All whole fruits and vegetables contain valuable fiber; it’s especially concentrated in the peel, so try to keep your apples and carrots intact. Vegetables with the highest fiber content include hardy veg like collard greens, kale, artichoke hearts, asparagus and broccoli. Soft fruits like raspberries, blueberries and blackberries are also great sources for fiber, as are avocado, mango and guava. And the humble apple is a fiber double-whammy, supplying both soluble and insoluble types.
By the way, don’t rely on fruit and veggie juices to supply your fiber needs: they usually have some or all of the fiber removed. And if you’re wondering why you have to rinse those tiny fruit particles out of your kencko mixer bottle after you use it, that’s how you can tell we didn’t take out any of that lovely fiber!
Rich prebiotic fiber sources - gut flora faves - include pungent veggies like garlic, onions and leeks, but also bananas and asparagus. Chicory root, very high in the prebiotic fiber inulin, is an extremely hip and healthy choice, while Jerusalem artichoke is a less cool but also beneficial source of inulin.