It’s something we’ve heard repeated for decades: eat more fiber, get more healthy.
But how well has this claim held up over the years?
After decades of research, the answer is: not great.
Fiber is probably less important than you’d think. If you eat whole, real food and few carbohydrates, you likely don’t need to increase your fiber intake. If you eat large amounts of processed food and added sugar or sweeteners, you may need a lot more to stay healthy.
But far be it from me to keep you from making your own decision.
Let’s look at the data so you can assess the research for yourself.
First: a quick overview of fiber
We hear the term ‘fiber’ thrown around all the time, but it’s a little more complicated than just ‘carbohydrates we can’t digest.’ Not all fiber is exactly alike, and not all forms have the same effect on your body.
There are three major ‘umbrellas’ to look at here:
- Solubility: Soluble fiber dissolves in water. Foods like blueberries and almonds are some of the most common examples. In contrast, insoluble fiber does not dissolve in water. Most grains and legumes have a heavy insoluble fiber content, as do potatoes, corn, and fruits with skin (like apples).
- Viscosity: Some types of fiber turn into a gel in your stomach, which isn’t absorbed by your digestive system. Oats and chia seeds are likely some of the most identifiable food items, as well as flax and peanuts. Non-viscous fiber doesn’t turn into this paste, which means it’s typically more digestible to the body. It’s more common in vegetables like broccoli, as well as nuts like almonds and pecans.
- Fermentability: If microbial activity can quickly break down a fiber, it’s considered highly fermentable and prebiotic (aka, grows your gut microbiota). Onions and cabbage are probably the most intuitive examples. Fibers that can’t or don’t break down quickly are considered nonfermentable. This includes food like lettuce, kale, and avocados.
So to summarize, soluble, non-viscous, fermentable fiber can be absorbed by your body and potentially put to good use. But insoluble, viscous, non-fermentable fiber cannot be digested and passes out of your digestive tract without providing any nutrients.
There was once a scientific consensus saying you needed both to stay healthy.
But the more research we’ve done, the wider the divide becomes.
Addressing both sides of the fiber debate
Most mainstream nutrition textbooks still claim that fiber is necessary to human health. But more and more scientists have called this into question.
Today, there are two distinct sides of the fiber debate:
The ‘fiber is essential’ crowd
Passionate defenders of ‘old guard’ science and highly educated in their own right. In their view, humans need fiber to healthily function as they age.
Let’s break down their evidence here:
- Fiber fights inflammation. The idea is that a high fiber intake can help you lose weight, which can help you modulate inflammation.
- Fiber modulates blood sugar spikes. High-fiber foods may blunt blood sugar impacts, which means a low-fiber diet could lead to hyperinsulinemia on the Standard American Diet.
- Fiber makes your gut biome more diverse. The more fiber you have in your diet, the more microbes you need to break it down or pass it along. Therefore, the more fiber you eat, the more diverse your biome is, and the healthier your gut must be.
- You might get heart disease without fiber. One study found that every seven extra grams of fiber per day reduced a person’s risk of cardiovascular disease by 9%.
- You need fiber to make short chain fatty acids (or SCFAs). These are thought to maintain the internal lining of your gut. Eating fiber creates more SCFAs, meaning the more fiber you eat, the healthier you are.
The ‘fiber is incidental’ crowd
Usually scientists, nutritionists, and metabolic health experts, including Dr. Nick Norwitz, who is at the forefront of current metabolic research. They find fiber to be incidental and even optional for human health. In some select cases, fiber elimination can be therapeutic.
Here’s the research for you to consider:
- You don’t need fiber to have a diverse biome. For example, one published case study compared the gut biome of a man on the carnivore diet to those following omnivorous diets — and discovered the man’s biome was equally as rich and diverse as his counterparts.
- You may not need fiber to blunt blood sugar impacts. If you’re already eating whole, real foods, you may not experience blood sugar spikes at all. Eating fiber would therefore be unnecessary, especially if you’re following a ketovore or carnivore diet.
- Fiber’s ‘diverse gut biome’ effect may not necessarily matter. Studies show that plant-based, fiber-rich diets may actually decrease diversity in gut biomes.
- Fiber isn’t necessary for SCFA production. Studies show that people on low-fiber diets have the same SCFA levels as those on higher fiber diets.
- Fiber doesn’t fight inflammation in all cases. Some studies show individuals have high inflammatory responses to fiber intake — meaning the more fiber they consume, the more inflammation buildup they experience.
This last point leads us to an interesting question:
Is fiber actually bad for you?
It was once standard practice to recommend high-fiber diets to those suffering from chronic bowel diseases. These days, however, we realize they may not need fiber to treat their symptoms. In many cases, it could make them worse.
A recent study discovered that stopping or reducing dietary fiber could address chronic idiopathic constipation (CIC) — and 100% of its participants eliminated bloating and straining. Other similar conditions, including treatment-resistant Crohn’s disease, have been successfully addressed with fiber-free diets.
There are also several case studies detailing how patients get IBS symptoms under control by increasing their protein and fat intake and decreasing carbohydrates. Several put their diseases completely into remission — all by removing fiber from their diet.
At the end of the day, it boils down to N = 1. If you are a fiber hyper responder who cannot tolerate large amounts, or if you’re someone suffering from IBS, Crohn’s disease, or a similar bowel disease, it might take sense to consume less fiber.
The start of a longer conversation
So do humans need fiber to be healthy? You be the judge.
If you’re eating mostly processed foods, research seems to point towards ‘yes.’ But if you’re eating whole, real food, following keto or carnivore, or suffering from IBS or chronic diseases, the answer may be ‘no.’
This, of course, is just the beginning of the conversation — we clearly have much more research to do. And as scientists work to get more answers, I recommend focusing on the three pillars of metabolic health:
- Eating whole, real food
- Exercising often
- Avoiding added sugar and processed ‘near food objects’
If you’re curious about experimenting with fiber, you might try testing a few different diets. Start gathering information through food logging, relevant blood testing, and if you’re genuinely curious, microbiota samples.
My hope for you is to feel empowered to understand and reclaim your metabolic health. Then, when you’re ready to go deeper down the rabbit hole, one of these resources may pique your interest:
- Is fruit bad for you?
- Should I stop eating eggs?
- Plant milk vs dairy milk: which is healthier?
- Red meat and metabolic health: what’s the truth?
