How to improve your microbiome with fiber and real food

Gut health can no longer be reduced to bacterial diversity. In the conversation with Simon Hill, Tim Spector explains why that way of measuring the microbiome has become too limited and how a more useful approach combines diet, metabolic response, and change over time. The message is not that you need to chase every microbe as an isolated marker. Your microbiome responds to the full pattern of what you eat, when you eat, and how much room you give to habits that support inflammation or recovery.

Why diversity alone is no longer enough

For years, the microbiome conversation leaned on a simple rule: more diversity means better health. Spector admits that this idea helped the field get started, but he also explains its limits. If every species counts the same, a problematic species can add points just like a beneficial one. That makes interpretation clumsy and means useful interventions, such as increasing fiber or improving diet quality, may not show up clearly in the result.

That is why his team changed direction. Instead of looking only at how many different microbes appear, they focused on a ratio between microbes linked to favourable patterns and microbes linked to unfavourable ones. To build it, they used a large dataset of about 35,000 people, detailed diet questionnaires, advanced sequencing, and validation across other countries. The result was a set of one hundred key microbes, fifty with positive associations and fifty with negative associations, tied to both diet and health markers as well as intervention response.

That shift matters because it moves the microbiome closer to a practical tool. Rather than treating it like a laboratory curiosity, it gets closer to real questions: if you improve meal quality, reduce ultra processed food, and increase plants and fiber, is your gut system moving in the right direction? For Spector, that answer is more useful than an abstract metric that only counts variety.

Which habits seem to improve the microbiome

If the episode makes one thing clear, it is that the microbiome responds better to consistent patterns than to isolated fixes. Spector keeps returning to plant variety, fiber, fermented foods, and polyphenols. He also repeats one concrete and memorable idea: try to eat 30 plants a week.

He does not only mean vegetables. Legumes, fruit, nuts, seeds, herbs, and spices all count. That variety matters because it feeds different microbial communities and increases the production of compounds that support the immune system and metabolism.

Polyphenols show up as another major lever. Spector highlights extra virgin olive oil and minimally processed dark chocolate as especially interesting foods, as long as they are not loaded with additives. He also mentions matcha and natto as personal examples of foods he once dismissed and now includes because of the evidence and their potential microbiome benefits.

Fermented foods do not replace fiber. They play a complementary role. According to the discussion, they may improve gut health through different pathways, including some that affect the immune system. That helps correct a common mistake: thinking that one functional food can make up for a poor diet. The overall pattern still matters most.

What to do about glucose spikes and dips

Another useful nuance is that it may not be smart to obsess over the glucose spike on its own. Spector says that in their data the later dip may be even more relevant than the initial peak. Roughly one in four people experiences a glucose drop a few hours after a high sugar or refined carbohydrate meal, and that drop is linked to greater hunger and higher calorie intake later.

That changes the question. Instead of looking only at the highest number after a meal, it makes sense to notice how you feel later, whether fatigue appears, whether appetite rises, or whether you want to keep snacking. It also reinforces the idea that the context of the plate matters more than demonising one ingredient. A little honey or sugar in someone who is metabolically healthy is not the centre of the problem. The real issue is the repeated pattern of meals that are low in fiber, protein, and healthy fats.

That is why the practical recommendation is not to live attached to a sensor. It is to build steadier meals:

• Start with plants and fiber.
• Add enough protein.
• Use high quality fats.
• Reduce ultra processed food and late night snacking.

How to use testing without becoming paranoid

Spector does not present the microbiome as a magical replacement for every classic lab marker. He presents it as a useful complement and as a tool that may be more sensitive for capturing early change. It can help identify individual responses, guide dietary intervention, and explain why two people react differently to the same food.

That does not mean everyone should measure everything all the time. A gut test or a continuous glucose monitor can help you learn patterns, but the most valuable lesson remains simple. If your diet is built on real food, plant variety, fermented foods, polyphenols, and a reasonable eating window, you are probably creating a better environment for your microbiome.

He also handles time restricted eating in a sensible way. He supports a moderate version, close to a ten hour eating window and a fourteen hour overnight fast, but makes it clear that it is not for everyone. In Zoe's large user study, some people did very well with it, some rejected it, and some landed somewhere in the middle. That reminder matters: personalisation does not mean making everything more complicated. It means recognising that real adherence matters as much as theory.

The useful summary is direct. Stop looking for shortcuts, stop arguing only about calories, and stop treating every food as a moral verdict. If you want better gut health, build a sustainable pattern with more plants, fewer ultra processed foods, and enough regularity for your microbiome to work in your favour.