Prebiotics and the gut microbiome

Our gut microbes are so important to us, it is essential that we feed them well. Prebiotics are what these microorganisms eat.

Definition of prebiotics:

‘Non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and this improves health’

    (Gibson and Roberfroid, 1995)

‘A substrate that is selectively utilised by host microorganisms conferring a health benefit’     (Expert consensus, 2017)

How they confer benefits to us:

•Feed beneficial bacteria and help them multiply

•Anti-inflammatory (interact with immune cells)

•Effect on epithelium – decrease permeability of lining of the gut

•Protect from invasion of gut pathogens (unwanted bugs!)

Sources of prebiotics include:

Inulin: artichokes, garlic, leeks, onions, wheat, rye and asparagus.

Fructo-Oligosaccharides (FOS): found in various fruits and vegetables, including bananas, onions, garlic and asparagus.

Resistant starch:  from grains, barley, rice, beans, green bananas, legumes and potatoes that have been cooked and then cooled.

Pectin: Good sources of pectin include apples, apricots, carrots, oranges Arabinoxylan: Arabinoxylan is found in cereal grains. For example, in wheat bran it makes up about 70% of the total fiber content

Guar gum: Guar gum can be extracted from guar beans, which are legumes

Human milk oligosaccharides: from breastmilk

Polyphenols: also has antioxidant properties and found in dark chocolate and linseed/flaxseed

Probiotic supplements

Manufacturers are not allowed to make health claims about prebiotics at this time. Two supplements currently used in research are:

  • Inulin supplements are sourced from Chicory root

  • Arabinoxylan oligosaccharides (AXOS) from wheat bran

reap the Benefits of prebiotics:

45g oats each morning reduces LDL cholesterol (the unwanted type) and increases the beneficial bacteria Bifidobacterium.

Possible side effects of prebiotics: Usually from supplemental prebiotics and too high doses



•Abdominal pain

•Loose stools and diarrhoea


Bottom line: increase your intake of prebiotics gradually. Include a wide variety of fruit, vegetables, nuts, seeds, grains and pulses each week - 30 different types a week can increase the variety of beneficial bacteria in your gut. A serving of a fruit or vegetable is 80g therefore eating large amounts of one type may cause unwanted gut symptoms.

Only eating whole foods will confer these benefits to your gut microbiome, so there is no magic pill I’m afraid.

Ruth Harvey