Part 1 of this three-part series on prebiotics introduced prebiotics as “food” for microbes in the gut, which in turn selectively stimulate the growth and/or activity of beneficial bacteria that colonize the intestine – the permanent bacteria from the first three years of life.
Bacteria ferment prebiotics to acids and gases, primarily. But not all beneficial bacteria can ferment all prebiotics in the gut. Prebiotics come in a variety of shapes and sizes, and require specific bacterial enzymes for processing (i.e. fermenting). No individual bacterial species has all enzymes to process all types of prebiotics. Not to worry: A healthy gut contains more than 800 different species of bacteria and hundreds of thousands of copies of various strains. Among the wide variety of beneficial bacteria in the gut, there are enough bacterial species that can ferment the wide spectrum of prebiotics in our diet.
Beneficial bacteria in the gut are dependent on a wide spectrum of prebiotics to grow, multiply, and work towards making us healthy. Without adequate amounts and a wide spectrum of prebiotic-rich foods in our diet, the biodiversity of our intestinal ecosystem reduces. Just like humans, bacteria need food to stay healthy, be active, and grow.
Generally, the spectrum of prebiotics consists of (brace yourself for some long, awkward terms) galactooligosaccharides (GOS), fructooligosaccharides (FOS)/oligofructose (OF), inulin, resistant starches, non-starch polysaccharides (NSP) and, to a lesser extent, some sugar alcohols. What do these terms mean with respect to food? Well, let’s explore each one of these prebiotics separately in detail.
“Saccharide” simply means sugar molecule, which is a carbohydrate. So oligosaccharides are nothing more than linear chains of simple sugars, either fructose, glucose, or galactose, 2-9 units long, that are bound together. These cannot be digested in the small intestine, so continue to the large intestine as “food” for good bacteria.
GOS are chains of galactose linked together with a glucose molecule at the end, and are a key component in human breastmilk. In breastfed infants, GOS are known to stimulate the growth of bifidobacteria, a bacterial species with very good health benefits. Recognizing this, some infant formulas are now supplemented with GOS. One would expect that babies fed GOS-supplemented infant formula would also have high growth of bifidobacteria. However, the growth of these species in formula-fed infants is less than that in breastfed babies. What does this conclude? No infant milk formula, no matter how well it is made and researched, can mimic the master design of women’s breastmilk for the health of infants. Infant formula is a runner-up to human breastmilk.
Beyond breastmilk, GOS are found in pulses, which are dried beans eaten cooked or canned, such as chickpeas and broad, cannellini, lima, and soya beans. Jerusalem artichokes, carrot juice, kefir, yogurt, and soy beverage are other GOS-rich foods to include in the diet over the lifespan. (Note: Soya beans are highly genetically modified.)
Fructans: Fructooligosaccharides and Inulin
FOS and inulin are subcategories of fructans. Fructans directly stimulate bifidobacteria species while indirectly stimulating many other non-bifido bacteria that are beneficial for health. FOS have a slightly different structure than GOS. Instead of chains of galactose, fructans are linear chains of fructose in varying lengths, ending with a glucose molecule. Specifically, FOS are short chains of fructose, 2-9 units long, while inulin is a longer chain of fructose, 10-60 units long. Foods rich in fructans usually have both types of fructans, FOS and inulin. These foods include chicory root, leek bulbs (white part), spring onion bulbs, garlic, yacon, onions, Jerusalem artichokes, globe artichoke, asparagus; and wheat, barley, and rye.
GOS and fructans are the well-known prebiotics owing to considerable research that has confirmed significant health impacts of these prebiotics on intestinal microbiota. Other types of oligosaccharides are also being explored as prebiotics for example, isomaltooligosaccharides (IMO), which is found in honey and some fermented foods. Research on the prebiotic health benefits of resistant starches, NSP, and sugar alcohols is not as established in sufficient detail as are GOS and fructans. Although research may be lacking, we can still intentionally include these in our diet, knowing that these do still have prebiotic effects. What exactly are resistant starch, NSP, and sugar alcohols and what are rich food sources? Well…
Starch is very long linear or branched chains of glucose molecules found in pasta, rice, potatoes, squash, bread, etc., and it varies in chain length and degree of branching. Usually digestion of starch begins in the mouth and is completed in the small intestine where it is also absorbed. Resistant starch, then, is chains of starch that are not absorbed in the small intestine of healthy individuals. Resistant starch is non-digestible by human enzymes for a variety of reasons. Good news: beneficial bacteria that live in our gut can digest/ferment resistant starch. Thus, RS serve as prebiotics, and is the most abundant sources of prebiotics in the western diet.
Foods high in resistant starch are pumpernickel bread, grainy or wholemeal rye bread, corn tortillas, raw potatoes, muesli, Ryvita crispbread, puffed wheat, raw unripe bananas, oats, white beans chickpeas, and lentils. Although I am not a promoter of cold, puffed or extruded cereals, Cornflakes and Rice Krispies cereals are high in resistant starch. In addition to these foods, resistant starch is formed when starchy foods, such as potatoes, rice, and pasta, are cooked then cooled. The way starch molecules realign after cooking makes these foods resistant to digestion by human enzymes. Pasta and potato salads, thus, have resistant starches,
Prebiotics, prebiotics, and more prebiotics…
Other prebiotics less researched for their prebiotics benefits are sugar alcohols and plant fibres. People often associate fibre with roughage and keeping our bowel movements regular. We get this type of fibre in foods from vegetables, whole grains, fruits, legumes, nuts, and seeds – practically any plant-based whole food. Sugar alcohols, such as sorbitol, xylitol, and mannitol, are found in stone fruits (peaches, plums, apricots) peaches, apples, prunes, raspberries, mushrooms, celeriac, pumpkin, and often in sugar-free diet foods.
Prebiotics in the kitchen
So, having explored the types of prebiotics, how can you vary the types of prebiotics in your diet? Here are a few more tips, as a continuation from last week:
- Add more pulses to you diet. Aim for at least ½ cup of lentils, beans or chickpeas every day. If these are not a standard part of your diet, start with 2 tablespoons of small pulses such as lentils or navy beans, avoiding the larger beans, such as kidney beans, in the beginning. As your body becomes accustomed to digesting pulses, you tolerance (i.e. absence of gas or bloating) should improve. Pulses are easy to hide in smoothies pureed sauces, and whipped mashed potatoes. Consider adding some on salads, to meat sauce, and soups. You can also puree beans to use in baking to reduce the fat content. Pulses Canada and this Pulse website are awesome resources for everything pulses.
- If you can tolerate potatoes (some of us have an intolerance to nightshade vegetables), consider making an oil-based potato salad (recipe next week) or one made with homemade mayo.
- Although pasta (gluten-containing or gluten-free) is enjoyable warm, cold pasta can be delicious too. Mix up a pasta salad with bow-ties or penne noodles for a cold lunch the next day with sliced spring onion bulbs, cherry tomatoes, diced cucumber, fennel, and olives. Chew to your microbiota delight!
The types of prebiotics we consume can be used to enrich our microbiota. Because bacteria have “food” preferences, it is best to consume a variety of prebiotic-rich foods. Even within each category of prebiotics – GOS, fructans, resistant starches, NSP, and sugar alcohols – there is a lot of variety. Eating a varied diet of whole foods, in general, promotes a diverse microbiota. Part 3 will wrap up this series on prebiotics, providing you the gram amounts of prebiotics in prebiotic-rich foods. My hope by the end of this series is that you’ll be confident knowing that you are building a healthy microbiota and protecting against disease.