Are Prebiotics good for our health?

Why the interest in Prebiotics?

We used to think of bacteria as bad for us. However, it seems that some bacteria are 'friendly' and good for our health and that, in general, the greater the diversity of bacteria in our gut the better. Prebiotics can help encourage the growth of 'friendly' bacteria - hence the interest in them.

What is the difference between Prebiotics and Probiotics?

Probiotics are ‘friendly’ live bacteria in foods like some yoghurts, dairy products and sauerkraut (fermented cabbage). They appear to be effective in helping manage some gastrointestinal conditions, such as Irritable Bowel Syndrome (IBS).

However their power tends to be limited when compared with prebiotics. This is because:

  • Different probiotics have different strains and concentrations of bacteria that have different properties. Only a minority of them have been tested properly in clinical trials to find if they were indeed effective. Also, some probiotic strains are destroyed by stomach acid. 
  • They are unsuitable for people who are allergic to dairy products or who have severe immune deficiency.

In contrast, Prebiotics aren't live bacteria. They are dietary fibres found in a number of plants – like bananas, garlic, onions, artichoke, chicory root, beans, peas, whole grains and apple skins.

What they can do is to nourish/fertilise the growth of ‘good’ bacteria in our lower gut and the large bowel. Unlike probiotics they aren’t vulnerable to stomach acid, so they can make it through to where they are needed.  

Prebiotics can probably help protect us against a number of clinical conditions (although more research is needed here) as well as potentially helping control our body weight

They are a relatively new discovery. They were first defined in the mid 1950s - as “non-digestible foods that benefit the host by supporting the growth and/or activity of one or a limited number of bacteria in the colon, thus improving host health”.  Although all prebiotics are fibre, not all fibre is prebiotic. Prebiotics: 

  • Resist the acid environment of stomach and absorption in the upper gastro-intestinal (GI) tracts
  • Are fermented by the intestinal microflora (bacteria);
  • Can stimulate the growth and/or activity of certain intestinal microbiota (bacteria) which in turn result in good health and wellbeing.

The health benefits of prebiotic intake may include:

  • Reducing the risk of bacteria-associated diarrhoea and how long symptoms last if you do get it
  • Lowering some risk factors for cardiovascular disease (CVD)
  • Strengthening the body's immune system

Could Prebiotics help prevent Obesity?

Research in humans is still in its early days but where people consume prebiotics (and other types of fibre) this appears to increase the diversity of bacteria in our gut. 

People who are obese tend to have less diversity of bacteria in their gut and less ‘friendly’ bacteria. For instance a 2006 article in Nature noted that two groups of ‘friendly’ bacteria are dominant in the human gut, the Bacteroidetes and the Firmicutes. However the relative proportion of Bacteroidetes is lower in obese people, whereas this proportion increases with weight loss on two types of low-calorie diet. This has led to the suggestion that more diversity and more ‘friendly’ bacteria can help prevent obesity – hence a potential role for prebiotics. As various types of fruit, vegetable and pulses have prebiotic qualities this suggests that ‘Five a Day’ could be good for controlling our weight as well as supporting our health.

Prebiotics are a type of fibre. The American Dietetic Association reports that high fibre diets make people feel fuller (so presumably less inclined to eat more) and have been linked to lower body weight. For example, one study reported that over a 20-month period, every 1 g increase in total fibre consumed per day, decreased body weight by 0.25 kg

Similarly, in a randomized, double-blind, placebo-controlled trial (the most rigorous type of research study, as it avoids either patient or researcher expectaions influencing the outcome) the effects of supplementation with Fructooligosaccharides (FOS), the main substance in Prebiotics, was studied in overweight and obese adults. The study was relatively small and short (forty-eight healthy adults with a body mass index of over 25, who received the supplement for 12 weeks). However, there was a reduction in body weight of 0.43 - 1.03 kg with FOS supplementation, whereas the control group experienced an increase in body weight of 0.31 - 0.45 kg over 12 weeks.

Could prebiotics help prevent Type 2 Diabetes?

There are many theories about the relationship between fibre intake and type II diabetes. For example, regularly consuming the recommended amount of fibre (including prebiotics) has the potential to reduce glucose absorption rate, prevent weight gain, and increase the load of beneficial nutrients and antioxidants in the diet, all of which may help prevent diabetes.

Numerous large-scale cohort studies (which research participants with a shared characteristic, like a similar age range) have suggested that eating more dietary fibre is associated with a reduced risk of type 2 diabetes. In a multi-ethnic cohort study which followed 75,000 people for 14 years, people who ate more than 15 g of fibre per day had significantly lower diabetes risk, although results sometimes varied by gender and ethnicity. 

A more recent, small scale study, published in 2015, also suggested that prebiotics could help people who already have type 2 diabetes manage their condition.

Possible side effects?

Prebiotics are a type of Dietary fibre. The NHS advises that we increase fibre intake gradually, as a sudden increase can lead to bloating and stomach cramps, and also advises talking to your doctor about the amount and type of fibre if you have IBS. Cooking can make food rich in dietary fibre easier to digest. 

Prebiotics in context

Prebiotics are, of course, just one factor potentially affecting our health – alongside factors such as environment, lifestyle and genetic predisposition. However, it is a factor we can all take advantage of, through the food we choose to eat.


More research is needed. However it seems:

  • There is growing evidence that prebiotics are good for our health
  • Prebiotics may also help us control our weight.
  • So add bananas, garlic, onions, artichoke, chicory root, beans, peas, whole grains and apples to your shopping list. 
  • Increase your intake gradually, to avoid side effects like bloating.

 Kayhan Nouri-Aria and Natnaree Kaewhin January 2017, next review date January 2021

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