Prebiotics Part 3: How much is just right?

The good news is prebiotics impact your health far beyond the gastrointestinal system. The bad news is not everyone tolerates prebiotics. This seems to be the way with most foods: some people thrive off certain foods and do poorly with others, hence, the wide variety of diets. One diet certainly does not fit all. Still, we all require the same essential nutrients to function optimally, which includes prebiotics. Some people tolerate prebiotics while others tolerate a much smaller dose. Regardless, prebiotics remain an essential nutrient for good bacteria in the gut, which in turn improves overall health. How do prebiotics improve our health? Well…

Short-Chain Fatty Acids

The most notable benefits of prebiotics relate to the byproducts of bacterial fermentation in the intestine, namely, short-chain fatty acids (SCFA): acetate, butyrate, and propionate. Acetate is processed in the liver, then shuttled to muscles for fuel. Butyrate is preferred as energy for cells that line the colon. Propionate is used by the liver to generate glucose that is released during fasting periods. These three SCFA’s combined have notable health benefits, such as:

  • Acidifying the intestine (lower pH), which
  • Protecting against colon cancer
  • Enhancing calcium absorption
  • Inhibiting growth of bad microbes (i.e. pathogens) in the gastrointestinal tract
  • Decreasing triglycerides and cholesterol production in the body
  • Relieving constipation
  • Stabilizing blood sugar
  • Reducing appetite leading to weight loss
  • Having anti-inflammatory effects

Let’s look at a few in more detail.

Stabilizes Blood Sugar

People with diabetes are not the only ones that benefit from stabilizing their blood sugar. It is helpful in preventing other chronic diseases, maintaining a healthy weight, optimizing energy, lowering inflammation, and minimizing acne. Prebiotics are key players in this since most are soluble fibre. Fibre decreases the rate that food in the stomach enters the intestine, which is where nutrients are absorbed. When carbohydrates are rapidly digested and absorbed, blood sugar rises, rapidly. Delayed absorption prevents carbohydrates from being absorbed all at once, thus stabilizing blood sugar. SCFA’s also contribute to this delayed emptying affect. In addition SCFA’s reduce the digestibility of carbohydrates, particularly starch, perhaps by inhibiting the initial digestion of starch in the mouth.

Appetite Regulation Leading to Weight Loss

Weight management is a complex science that requires addressing many facets in life, the most significant being food selection. Prebiotic-rich foods influence appetite-regulating hormones independent of tempting junk foods that make us salivate. Specifically, propionate stimulates hormones, peptide YY and GLP-1, that signal fullness, or satiety, while decreasing another hormone, ghrelin, that signals hunger. So if your junk-food cravings are high, consider whether you have had your daily dose of prebiotic-rich foods, which naturally help curb hunger.

Strengthens Immunity

We all could use a stronger immune system to fight off common colds, protect against flues and infections, or prevent illnesses related to immune dysregulation. Prebiotics strengthen immunity indirectly by elevating the number good bacteria in the gut. Cross-talk between intestinal cells, beneficial bacterial cells, and immune cells strengthen immunity.

Anti-Inflammatory Effects

Inflammation is an immune response related to gut microbiota, which is linked to obesity, type 2 diabetes, fatty liver, insulin resistance, irritable bowel syndrome (IBS), and inflammatory bowel disease. It is also behind common acute symptoms of arthritis and injury, such as pain, redness, soreness, swelling, and stiffness. Prebiotics reduce chronic and acute inflammation via SCFA’s. Butyrate, in particular, reduces inflammation by blocking pro-inflammatory signals.

The Bad: When prebiotics don’t play nice…

Increased calcium absorption, disease-protection, cholesterol reduction, stabilized glucose, weight loss, stronger immunity, anti-inflammatory effects sounds great – well at least for most people. Introducing prebiotics into your diet is best tolerated when done gradually. It will take time for intestinal microbes to adapt to new foods. Once your microbes have adapted, you’re on your way to a healthy microbiota.

For people with IBS, small amounts of prebiotics trigger painful, unwelcomed symptoms, including diarrhea, bloating, gas, and gastrointestinal pain. These symptoms arise from impaired ability to clear gases formed through bacteria fermentation and the additional fluid load in the intestine due to osmosis. For 75% of people with IBS, a diet that reduces fermentable carbohydrates and poorly absorbed fructose is effective at reducing these symptoms and improving quality of life. However, the microbiota suffers since prebiotics are drastically reduced. A study investigating the composition of intestinal microbiota in people on this therapeutic diet showed a 6-fold reduction in Bifidobacteria, a beneficial bacterial species (1). Good news: most people who use this diet can systemically increase the amount of prebiotics, depending on their tolerance.

What amount of prebiotics should we target?

One bundle (about 400 grams) of asparagus will give you 10 grams of prebiotics, enough to meet the prebiotic recommendation for the whole day. But who would eat a whole bundle of asparagus?

For the vast majority of people without IBS, the International Scientific Association for Probiotics and Prebiotics recommends at least 5 grams of fructans and glucooligosaccharides, combined (2). Less than this amount is insufficient to induce prebiotic effects described above. However, studies on prebiotic benefits often note results with prebiotic doses between 5-20 grams/day. More than 20 grams/day may induce gastrointestinal symptoms in healthy individuals (3). Comparing the two recommendations, it may be prudent for healthy individuals to strike a happy medium by aiming for 10 grams/day.

The content of fructans and galactooligosaccharides in the table below should help you plan for 10 grams of prebiotics per day. I’ll warn you: achieving this amount is a stretch. The wide variation in fructans content is due to storage time and storage temperature, food variety, seasonal variation, and climate (3). All foods listed below were analyzed raw; however, there is normally only slight variations of fructans content between cooked, fried, baked, and raw forms. Be aware that 10 grams of prebiotics is equivalent to 400 g of bread/grains (13 slices of bread), 1 lbs. of asparagus (1 bundle), 15+ green bananas, or 1 large onion. Sounds like a lot? Yes, it is, yet meal planning or a registered dietitian can help.

Sources

  1. Stauncher HM and Whelan K. Altered gastrointestinal microbiota in irritable bowel syndrome and its modification by diet: probiotics, prebiotics and the low FODMAP diet. Proc Nutr Soc 2016;75(3):306-18.
  2. International Scientific Association for Probiotics and Prebiotics: Prebiotics accessed on May 17, 2017. http://isappscience.org/prebiotics/.
  3. Muir J et al. Fructan and free fructose content of common Australian vegetables and fruit. J Agric Food Chem 2007;55:6619-6627.

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