Only around 4% of UK adults hit the recommended 30g of fibre a day – so on paper, a trend that gets people eating more of it should be a win. But as fibremaxxing floods social media feeds, gut health scientist Dr Megan Rossi warns that ramping up too fast can backfire, leaving people bloated and convinced they’re “intolerant” to a nutrient their gut simply needs time to adapt to. Here, the King’s College London researcher and founder of The Gut Health Doctor talks us through the real science behind fibre, diversity, and building a truly “fibre fit” gut.
What is your take on the fibre maxxing trend?
I see both the positives and the negatives. The biggest positive is that it’s finally put fibre on people’s radar. That’s important because only around 4% of UK adults meet the recommended 30g of fibre a day, despite fibre being one of the most important nutrients for gut health.
The downside is that many people are dramatically increasing their fibre intake overnight. In clinic, I often see people develop bloating or discomfort as a result, then assume they’re intolerant to fibre. In reality, it’s usually not the fibre itself that’s the problem. It’s the speed at which they’ve increased it. Your gut needs time to adapt.
What are the benefits of increasing fibre intake for gut and overall health?
Unlike most nutrients, fibre isn’t there to nourish us directly. It nourishes the trillions of microbes living in our gut. When these microbes ferment fibre, they produce compounds that support gut health and influence everything from immune function to metabolic and brain health.
Higher fibre intakes are consistently associated with a lower risk of a wide range of chronic diseases, including heart disease, type 2 diabetes, bowel cancer and depression. It’s one of the strongest dietary predictors of long-term health.
How do you recommend people increase their fibre intake?
Think of it like training for a marathon. You wouldn’t go from sitting on the sofa to running 26 miles overnight, and your gut works the same way. I call this becoming “fibre fit”.
Increase fibre gradually and listen to your body. For many people, adding around half a cup of vegetables or legumes each week works well. Those with more sensitive guts may need to increase by even smaller amounts. Slow and steady allows your gut microbes to adapt and helps minimise bloating.
Beyond oats and berries, what are some underrated high fibre foods?
Rather than fixating on one “superfood”, I’d focus on diversity. Different gut microbes thrive on different types of fibre, so variety is far more important than eating lots of one food.
Aim to include foods from my Super Six each day: wholegrains, vegetables, fruit, legumes, nuts and seeds, and herbs and spices. Great examples include avocado, lentils, chickpeas, walnuts, almonds with the skin on, and seeds like chia or flaxseed.
A common complaint is ramping up fibre too quickly and ending up bloated. What’s your protocol for building tolerance?
Again, this comes back to becoming fibre fit. If someone struggles with chickpeas, for example, I’d suggest starting with just one tablespoon a day for a week. Week two is to increase to two tablespoons per day, and so on. If symptoms become uncomfortable, simply reduce the amount slightly, allow your gut to settle, then build up more slowly. The goal isn’t to avoid fibre. It’s to help your gut adapt to it, so you can then reap the health benefits.
Your 30 Plant Points approach focuses on diversity rather than volume. Where do you think the debate goes wrong by focusing on grams rather than variety?
Both matter. Hitting your fibre target is important, but where that fibre comes from is equally important. Often in clinic I see people relying on a fibre supplement and expecting the same benefits as eating a wide variety of plant foods. While certain supplements may have a role for some people, they can’t replicate the incredible diversity of fibres and plant compounds naturally found across different foods. We know there are close to 100 different types of dietary fibre, each interacting differently with our gut microbes.
This is exactly why our team at King’s College London is researching the impact of plant diversity on health.
Which types of fibre are best for your microbiome?
There’s no single “best” fibre because different microbes prefer different types. That’s why variety consistently outperforms focusing on one fibre source.
The simplest approach is to eat a diverse range of plant foods each week, aiming to include foods from the Super Six every day. That naturally provides the different fibres, prebiotics and polyphenols your microbiome needs to thrive.
Some argue fibre isn’t essential because people with Crohn’s disease or IBS often feel better when they remove it. How do you respond?
The long-term evidence overwhelmingly supports fibre as one of the most protective components of our diet. People who eat more fibre consistently have lower risks of chronic disease and premature death.
That said, during active inflammation, such as a Crohn’s flare, or during periods when IBS symptoms are particularly severe, temporarily reducing certain high fibre foods may help manage symptoms. The key word is temporarily. As inflammation settles, gradually reintroducing fibre is important because avoiding it long term can further reduce microbial diversity and potentially worsen gut health over time. In fact, for many people with Crohn’s disease in remission, a higher fibre intake appears to be beneficial.
If you had one piece of advice for people caught between fibre maxing and keto, what would it be?
Look at where the human evidence is strongest. Decades of research consistently show that diets rich in a wide variety of fibre-containing plant foods are associated with better long-term health, including lower risks of chronic disease, improved mental wellbeing and greater longevity.
I don’t think fibre maxxing is necessarily making healthy eating more complicated, but it can oversimplify the message. More fibre isn’t always better if you increase it too quickly. Your gut benefits most from gradual, consistent buildup over time.
What does a balanced meal look like for you?
I always try to include foods from as many of the Super Six on my plate, so I’m feeding a wide range of gut microbes. That might be wholegrains, mixed vegetables, legumes, herbs, nuts or seeds, alongside a source of oily fish. We know omega-3 fats aren’t just supportive of mental health but gut health too.
