“The dark side” of fiber? why prebiotics can damage the gut microbiome and increase cancer risk

Fiber rich foods feed the gut Microbiome and elongate life – how about prebiotics or fiber supplements?

In light of my upcoming book about diet and the Microbiome and my online course series I looked at the science.

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The studies reveal: fiber supplements do not have the same health benefits as fiber rich foods.

Here are 3 reasons why.

We have to eat fiber – otherwise we starve the Microbiome, get constipation and die earlier.

But some fiber can be harmful.

Despite consistent evidence from prospective epidemiologic studies that dietary fiber intake has a protective effect against various diseases such as cardiovascular disease (CVD),

the effects are only seen with fiber from food intake rather than from isolated fiber supplements.

1 – Antioxidants are lost without fiber

A recent study suspects that the bioactive compounds such as polyphenols, bound to the fiber structure in foods, deliver the real health benefit beyond the fiber. However, when isolated, polyphenol compounds and the natural 3-D structure of dietary fiber is lost when industrially processed.

They found that industrial food processing and extracting the dietary fiber led to a 30% loss of phenol compounds in foods.

The researchers caution that

“isolating one component {such as fiber} may overlook the combined health benefits of the whole food matrix”.

2 – Dietary fiber protects against cancer – but not “prebiotics” fiber supplements

For example, the influential Women’s Health Initiative study following more than 160000 women documented more than 3000 colorectal cancer cases within a time period of 15 years revealed that fiber supplements had no health benefit on colorectal cancer protection, as opposed to fiber from whole foods that is well documented.

Even worse, they found insoluble fiber supplements increased cancer risk by 2,8 – times.

The researchers suggest “These findings do not support the promotion of prebiotic fiber supplements to reduce colorectal cancer risk or colorectal cancer mortality”.51

3 – Prebiotics change the gut microbiome and may cause gut inflammation and cancer

It is not quite clear yet whether isolated dietary fibers such as food supplements, including inulin or others, may even exert dangerous side effects on the human body

In several preclinical lab studies on mice, the supplementation of the soluble fiber inulin – however not insoluble fiber – in their diet, revealed that “concentrated” isolated fiber supplements are metabolized differently by the gut microbiota than the fiber from whole foods , which induced liver cancer.

This launched a hot debate in the scientific literature, which the researchers suggested

“enrichment of foods with fermentable fiber should be approached with great caution as it may increase the risk of HCC (liver cancer)“

Another preclinical study confirmed that inulin fiber supplementation changed the microbiome metabolism from anti- to pro-inflammatory and resulted in allergy-like gut inflammation.

How to safely eat fiber

Although, there may be benefits of fiber supplements to improve digestion in the short term and for research purposes,

to receive the full health benefits of fiber such as feeding the gut microbiome and reduce cancer and disease risk,

it is important to get the dietary fiber from its natural source:

whole plant-based foods.

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