Prebiotics – What makes them different from Probiotics?

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The mystery of prebiotics

One of the most underappreciated topics in nutrition is prebiotics. While vitamins and other nutrients are covered in hundreds of books and articles, prebiotics are hardly mentioned. While many people are now quite familiar with the concept of probiotics, they have little knowledge about prebiotics [1]. This is surprising given the potential health benefits of prebiotics and their ability to regulate many processes in the body.

What are prebiotics?

Back in 1995, researchers defined prebiotics as a non-digestible food ingredient stimulating the growth of specific bacteria in your colon. [2] Nearly 10 years later they updated their prebiotic concept and suggested that prebiotics:

  • Resist gastric acidity, hydrolysis by mammalian enzymes and gastrointestinal absorption (non-digestible)
  • Are fermented in the colon by the intestinal microflora
  • Stimulate the growth of intestinal bacteria associated with health and wellbeing

A food ingredient has to meet all three criteria to be recognized as a prebiotic.

Food ingredients which have a prebiotic effect include inulin-type fructans (fructo-oligosaccharides, inulin and oligofructose) as well as galacto-oligosaccharides (GOS). Many of them are widely distributed throughout the diet – especially in vegetables, grains, and legumes. [4, 8]

Additionally, all prebiotics are dietary fiber, but not all kinds of dietary fiber have a prebiotic effect. They have to meet all aspects of the definition. [4]

Prebiotic foods list

If you want to increase your prebiotics intake, just check the following prebiotic foods list. All the foods include prebiotics naturally. [4]

Source Prebiotics included (ordered by proportion) FODMAPs (based on Monash University)
Apple Inulin, Fructo-oligosaccharides High FODMAP
Asparagus Inulin, Fructo-oligosaccharides High FODMAP
Banana (under-ripe) Resistant starch, inulin Low FODMAP
Savoy cabbage Inulin High FODMAP
Chickpeas Inulin High FODMAP
Chicory root Inulin High FODMAP
Dandelion greens Inulin, Fructo-oligosaccharides High FODMAP
Garlic Inulin, Fructo-oligosaccharides High FODMAP
Green beans Galacto-oligosaccharides Low FODMAP
Green peas Galacto-oligosaccharides High FODMAP
Artichokes Inulin High FODMAP
Jicama root Inulin High FODMAP
Leek Inulin, Fructo-oligosaccharides Leek bulb: High FODMAP
Leek green: Low FODMAP
Lentils Galacto-oligosaccharides High FODMAP
Onions Inulin, Fructo-oligosaccharides High FODMAP
Soybeans Galacto-oligosaccharides High FODMAP
Wheat Fructo-oligosaccharides High FODMAP

Prebiotics vs. Probiotics – What’s the difference?

Prebiotics act as food for the gut microbiome and the 1000 different species of bacteria living in your colon [4, 5]. This includes the probiotics you might take in form of supplements or probiotic foods. Consequently, prebiotics and probiotics work hand in hand to improve your health by influencing the microbiota and the activity of your intestinal tract. They also increase the presence of good bacteria in your gut, namely lactobacilli and bifidobacteria. Furthermore, the health of your gut is closely connected to your overall health which means that prebiotics (also in combination with probiotics) have several benefits.

What are the benefits of prebiotics?

Prebiotics for improved digestion and better gut health  

Prebiotics do not only promote the growth of good bacteria and thereby improve your intestinal microflora. They also help with bowel movements. Prebiotics are dietary fiber and thus they increase the stool weight by binding water and increasing the bacterial mass from fermentation. The stool also becomes softer which makes defecation easier. It also reduces the transit time through the digestive tract. Due to these properties, prebiotics can be used to prevent or treat constipation. [4]

Prebiotics for Irritable Bowel Syndrome

Prebiotics do not only work for generally healthy people who want to improve their digestion, but also for people suffering from chronic digestive diseases like the Irritable Bowel Syndrome (IBS). Small studies have shown that an intervention with prebiotic supplementation for IBS patients can alter the microbiota favourably. Consequently, prebiotics can improve IBS symptoms and help stabilize the weakened digestive tract. [8]

Prebiotics help with inflammation and immune function

Several studies have explored whether prebiotics can reduce inflammation and improve the immune function. One study showed that people taking prebiotics two weeks before they were travelling to destinations with medium to high risk for traveler’s diarrhea had fewer and less severe attacks of diarrhea. [4] Moreover, prebiotics intake can reduce the amount of C-reactive protein, a biochemical marker for inflammation. In addition, prebiotics increase the production of SCFAs (short-chain fatty acids) which play an important role for the modulation of metabolic and immune processes. They also help with maintaining intestinal health. However, we need more large-scale studies to provide meaningful evidence, for example for the effect of prebiotics on immune cell activity. [6]

The effect of prebiotics on body weight

There is still no magic pill to lose weight, but first research results suggest that prebiotics, as dietary fiber, can help with faster satiation. Usually fiber-rich foods take more time to chew which encourages the production of saliva and gastric acid which may boost gastric distention. [4] Moreover, the upper and lower gastrointestinal tract release satiety-related hormones while the food moves through them. The hormones are regulated by the above-mentioned SCFAs. Prebiotics increase the production of SCFAs and thereby stimulate the secretion of hormones which reduce appetite and positively increase insulin sensitivity. Additionally, the increased production of lactobacteria may reduce the storage of body fat. Again, we need more robust studies to assess the efficacy of prebiotics for the use of weight reduction. [6]

Prebiotics are said to lower the risk for cardiovascular disease

Both higher LDL cholesterol (bad cholesterol) and blood fat (called TAG) levels are associated with higher risk for cardiovascular disease. It was claimed that prebiotics can reduce both values, but recent studies have found no change in the level of LDL or total cholesterol. Results for blood fat have been contradictory – half of the studies reported a significant reduction, while the other half did not. [6]

Prebiotics for type II Diabetes

Several large-scale studies have explored the relation between dietary fiber intake and the risk to develop type II diabetes. Eating more than 15g of fiber per day therefore reduces the risk to develop type II diabetes. Whether the intake of prebiotics also positively influences your glucose levels after eating a meal is still not clear.

What are the side effects of prebiotics?

Dietary fiber cannot only help with constipation, but can also cause it. The reason is that fiber binds water. Thus, you should take care to drink enough water when eating high-fiber foods. Apart from that, taking prebiotics should not cause any side effects for healthy people.

Possible prebiotic side effects for people with IBS

However, prebiotics can be a two-edged sword for people suffering from IBS or a sensitive stomach. On the one hand, prebiotics can reduce IBS symptoms. On the other hand, some prebiotics like inulin and GOS are FODMAPs which can be symptom triggers for IBS. So while the low FODMAP diet recommends to eliminate FODMAPs for IBS patients, various high FODMAP oligosaccharides are also the most effective prebiotics to treat IBS symptoms. [7]

Additionally, there is another paradox. Both taking prebiotics and the low FODMAP diet can reduce IBS symptoms, but the former increases the concentration of bifidobacteria in the colon, while the latter decreases it. [8] However, decreasing the amount of good bacteria in your gut is not a good long-term solution because your microbiome becomes less diverse. Hence, you should find out which FODMAPs are actually causing your symptoms, instead of eliminating them all for good. Monitoring the phases of your FODMAP diet closely is therefore a good idea. And for the high-FODMAP prebiotics that are triggering mild to no symptoms, consider eating smaller amounts. You should then be able to profit from a diverse microbiome with reduced IBS symptoms.

Recommended intake

At the moment there is not enough evidence to make general dietary recommendations regarding prebiotics. However, first supplementation studies suggest that you need to add an additional 5–20g of prebiotics per day to promote a healthy microbiome. For Europeans who take about 10g of inulin and oligofructose per day, this would mean up to doubling the daily intake. [8] Furthermore, both the DGAC (Dietary Guidelines for Americans Committee) and the EFSA (European Food Safety Authority) have stipulated  daily nutritional goals for dietary fiber in general. The DGAC recommends intakes of 28g per day for women and 33.6g per day for man [9] whereas the EFSA recommends 25g per day for both men and women. [10] Most Americans and Europeans, however, only consume half of the recommended levels. [4]

References
  1. Betz, M., Uzueta, A., Rasmussen, H., Gregoire, M., Vanderwall, C. and Witowich, G., 2015. Knowledge, use and perceptions of probiotics and prebiotics in hospitalised patients. Nutrition & dietetics, 72(3), pp.261-266.
  2. Roberfroid, M., Gibson, G.R., Hoyles, L., McCartney, A.L., Rastall, R., Rowland, I., Wolvers, D., Watzl, B., Szajewska, H., Stahl, B. and Guarner, F., 2010. Prebiotic effects: metabolic and health benefits. British Journal of Nutrition, 104(S2), pp.S1-S63.
  3. Gibson G.R., Probert, H.M., Van Loo, J., Rastall, R.A. and Roberfroid, M.B., 2004. Dietary modulation of the human colonic microbiota: updating the concept of prebiotics. Nutrition research reviews, 17(2), pp.259-275.
  4. Slavin, J., 2013. Fiber and prebiotics: mechanisms and health benefits. Nutrients, 5(4), pp.1417-1435.
  5. Hutkins, R.W., Krumbeck, J.A., Bindels, L.B., Cani, P.D., Fahey, G., Goh, Y.J., Hamaker, B., Martens, E.C., Mills, D.A., Rastal, R.A. and Vaughan, E., 2016. Prebiotics: why definitions matter. Current opinion in biotechnology, 37, pp.1-7
  6. Kellow, N.J., Coughlan, M.T. and Reid, C.M., 2014. Metabolic benefits of dietary prebiotics in human subjects: a systematic review of randomised controlled trials. British Journal of Nutrition, 111(7), pp.1147-1161.
  7. Brouns, F., Delzenne, N. and Gibson, G., 2017. The Dietary Fibers–FODMAPs Controversy. Cereal Foods World, 62(3), pp.98-103.
  8. Staudacher, H.M. and Whelan, K., 2016. Altered gastrointestinal microbiota in irritable bowel syndrome and its modification by diet: probiotics, prebiotics and the low FODMAP diet. Proceedings of the Nutrition Society, 75(3), pp.306-318.
  9. US Department of Health and Human Services; US Department of Agriculture., 2015. 2015-2020 Dietary Guidelines for Americans. 8th ed. Washington, DC: US Dept of Health and Human Services; http://www.health.gov/DietaryGuidelines.
  10. EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA). 2015. Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre. EFSA Journal 2010;8(3):1462 [77 pp.]. doi:10.2903/j.efsa.2010.1462.
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