Polyphenols and Gut Health

Polyphenols are plant compounds that may support gut health, reduce inflammation and contribute to overall health. They are not vitamins, minerals or fibre. Instead, they are secondary plant metabolites that plants produce for their own protection, such as defence against UV light or insects.

There are around 10,000 different polyphenols. They are usually grouped into flavonoids and non-flavonoids. Flavonoids make up the largest group and are found in many colourful fruits and vegetables. This group includes flavones, flavonols, isoflavones and anthocyanins. Non-flavonoids include phenolic acids, lignans and stilbenes.

Bioavailability of Polyphenols

Polyphenol absorption can vary a lot. Some have very low bioavailability, while others can be absorbed at much higher rates.

Although some absorption occurs earlier in digestion, a large amount happens in the large intestine. Gut bacteria break polyphenols down into smaller metabolites, which the body can then use. Because of this, a person’s microbiome can influence how well they absorb and respond to polyphenols.

Dietary fat may also improve absorption. For example, pairing vegetables with extra virgin olive oil can help increase the amount of certain polyphenols the body absorbs.

How Polyphenols May Support Gut Health

Polyphenols may support gut health through several pathways. These include prebiotic-like effects, anti-inflammatory signalling and improved gut barrier integrity.

Prebiotic-Like Benefits

Many polyphenols reach the large intestine intact. Once they arrive there, they can act as fuel for gut bacteria.

This can help increase beneficial bacteria such as Lactobacillus and Bifidobacteria. As these bacteria increase, microbial diversity may improve and markers of gut inflammation may reduce.

This effect works in a similar way to fibre, although the mechanism is slightly different.

Butyrate Production

One downstream effect of improved gut bacteria is greater butyrate production.

Butyrate is a short-chain fatty acid produced when gut bacteria ferment certain substrates. It acts as a key fuel source for colon cells and supports gut health in several ways.

For example, butyrate may help reduce inflammation, support colon cell integrity and regulate immune function.

Animal research strongly supports this link. Human research also looks promising, but it is harder to interpret. This is because polyphenol-rich foods are often high in fibre too. So, when people eat more polyphenols, they often eat more fibre as well.

Anti-Inflammatory Effects

Polyphenols also appear to have direct anti-inflammatory effects.

One key pathway involves NF-kB, which helps regulate inflammatory gene expression in the body. When this pathway stays chronically active, it may contribute to low-grade inflammation.

Polyphenols may help reduce activity in this pathway. Human randomised controlled trials have shown measurable changes in inflammatory markers such as CRP, IL-6 and TNF-alpha. The effects are not always large, but they may still be relevant.

Gut Barrier Integrity

Polyphenols may also help support the gut barrier.

They appear to upregulate proteins that reduce intestinal permeability, which is sometimes referred to as “leaky gut”. This could be relevant for conditions such as IBS and IBD.

However, the direct evidence in these areas is still limited. The current research looks positive overall, but there is not strong evidence showing that polyphenols dramatically improve symptoms in IBS or IBD.

Food Sources of Polyphenols

Polyphenols are found in a wide range of plant-based foods.

Common sources include:

Berries
Colourful fruits and vegetables
Dark chocolate
Extra virgin olive oil
Green tea
Legumes
Red onion
Cloves
Star anise
Turmeric

In some cases, specific foods may provide specific benefits. For example, blueberries contain anthocyanins, which may play a role in cognitive function. However, for overall health, eating a variety of polyphenol-rich foods makes the most sense.

Cooking, Storage and Bioavailability

Preparation and storage can affect polyphenol content and absorption.

Cooking tomatoes can increase the bioavailability of some phenolic compounds. Fermentation may also help, as foods such as kimchi, kefir and sourdough can pre-convert compounds into a more absorbable form.

Frozen berries retain polyphenols well. However, cooking with berries can reduce some of their polyphenol content.

Some polyphenols, such as certain flavonoids, are heat-sensitive. Because of this, long cooking times or high heat may reduce polyphenol levels in some foods.

Extra virgin olive oil is higher in polyphenols than regular olive oil. Its polyphenols hold up reasonably well under heat, although longer cooking times and higher temperatures can reduce them.

Ways to Improve Polyphenol Absorption

Pairing polyphenol-rich foods with fat can improve absorption. This is one reason why meals that combine vegetables with extra virgin olive oil may work well.

Curcumin, the main active compound in turmeric, is technically a polyphenol. It has poor absorption on its own, but black pepper can significantly improve how much the body absorbs.

Vitamin C may also improve polyphenol absorption. In practice, this often takes care of itself because many polyphenol-rich foods already contain vitamin C.

Practical Takeaways

A varied intake of plant foods can help increase polyphenol intake. Aiming for a broad range of plant foods across the week is a useful starting point.

Small swaps can also help. For example, choosing extra virgin olive oil instead of regular olive oil can increase polyphenol intake. Adding more colourful fruits and vegetables to meals can also make a difference.

Other simple options include drinking green tea, choosing berries more often, using herbs and spices, and selecting a higher-percentage dark chocolate if that suits your taste.

Overall, polyphenols are another reason to include a variety of plant foods in your diet. They may support gut bacteria, inflammation, gut barrier health and broader health outcomes.