With the popularity of low carbohydrate eating patterns, such as paleo and ketogenic, there seems to be ongoing disagreement about what constitutes the “ideal” balance of macronutrients (carbohydrates, protein, and fat) for supporting optimal health. 

Despite recommendations by the Institute of Medicine to consume 45-65 percent of our daily caloric intake from carbohydrate sources, it seems that when an individual wants to shed some extra weight, the usual advice is to just “cut out carbs.” Considering that carbohydrates are technically sugars, it’s no surprise there is confusion and debate about their benefit or potential harm.

But are all carbs really “bad”? 

Because carbohydrates are ubiquitous in plant foods, eliminating them from our diets is virtually impossible. The question that remains, however, is whether greatly reducing carbohydrate intake overall is good for our health. 

This article dives into some of the science around different carbohydrate sources and what value carbs bring to our wellness goals. As the science continues to highlight the critical importance of diverse and abundant colonies of gut microbiota for overall health, we will specifically explore the impact that carbohydrates have on the trillions of symbiotic bacteria that reside within us.

Not all carbohydrates are created equal: Complex vs. simple

Ideally, dietary carbohydrates primarily come from the plant foods that we consume, namely fruits, vegetables, legumes, and grains; but carbs can also come from highly refined sources, like soda, candy, cookies, cakes, and white bread. Although these sources can vary dramatically, carbohydrates are indeed made up of sugar molecules, which are the body’s preferred source of fuel to make cellular energy, particularly when it comes to high output activities that require skeletal muscle contraction.1

Not all carbohydrates are created equal, however. For example, the carbohydrates sourced from table sugar are metabolized very differently than carbohydrates from a leafy green salad or a bowl of pasta, due to major differences in their chemical composition and structure. 

Carbohydrates are either “simple” or “complex,” which refers to the number of sugar molecules strung together, with simple carbohydrates represented by monosaccharides (single sugars) or disaccharides (double sugars), and complex carbohydrates comprised of a chain of sugar units strung together. The longest of the complex sugar chains are called polysaccharides, which includes plant cellulose, the “roughage” found in leafy greens, as well as the starch found in bananas, potatoes, and pasta.

Simple sugars, like glucose (a monosaccharide that is the primary source of fuel for our bodies) or sucrose (table sugar – a disaccharide made up of glucose and fructose) require little effort to break down and therefore deliver instantly accessible sugar into the bloodstream for our bodies to convert into energy. These simple sugars shouldn’t be broadly labeled as “bad” because we rely on a certain amount for our bodies to function. However, because consistently flooding our bodies with large amounts of these readily accessible sugars can cause blood sugar spikes and can have long-term detrimental effects on our metabolism, the focus should be on ingesting complex carbohydrates.

Complex carbohydrates, such as those delivered from whole grains or vegetables, require energy (and digestive enzymes) for our bodies to break down into simpler, more usable forms. Therefore, they release their sugars into the bloodstream at a slow and steady rate, helping to maintain a stable blood sugar level. Starch, which contains hundreds of glucose units strung together, is metabolized more slowly than table sugar, providing a “time-released” quality, which is particularly valuable for supporting sustained energy during a workout. 

What remains of complex carbohydrates after digestion? 

A significant benefit of complex carbohydrates is provided by what remains intact after digestion. Because our digestive system is not equipped with the enzymes needed to break down the fiber and resistant starch in complex carbohydrates, these compounds pass through the stomach and small intestine, making it to the large intestine intact, where they play an essential role in overall gut health.

The importance of fiber

Fiber provides the “bulk” that functions to increase our sense of fullness, as well as the roughage that supports good transit time, healthy elimination, and stool quality. Fiber also binds to toxins and removes waste products from the body.

There are many different types of fiber, each with varying characteristics of water solubility, viscosity, and fermentability by gut bacteria.2

Starch vs. resistant starch

Starch is found in a variety of fruits, vegetables, grains, and legumes, and it sometimes gets a bad rap due to its high “sugar content.” Although digestive enzymes can break down most starch into simple sugars to use as fuel, some escapes digestion and acts similarly to dietary fiber in the large intestine.3 Resistant starch, as the indigestible form is called, is commonly consumed from legumes and whole grains, particularly when cooled after cooking, and it’s also present in unripe bananas.3

Prebiotics, probiotics, postbiotics, oh my!

Some fiber and resistant starch have also been found to have distinct prebiotic benefits, meaning they serve as food sources for the beneficial bacteria in our guts.3,4

Although we can’t digest some of these long sugar chains, many of the bacterial species in our guts are specialized to do precisely that, and they have adapted specifically for their capacity to digest carbohydrates.5 

Supplementing with clinically researched probiotic formulations, such as Thorne’s FloraSport 20B®, offers a great way to nourish your microbiome by “seeding” it with live bacterial species.

Another avenue to helping our internal ecosystem flourish is to “feed” our beneficial bacteria prebiotic fibers, which provide the nourishing substrate for them to create new compounds, known as fermentation end products, or “postbiotics.” These, in turn, yield unique benefits back to us, their host!6,7

The term postbiotic refers to the metabolites created by gut bacteria as a part of the fiber fermentation process and can include heat-killed bacteria (found in fermented food for example; heat killing does not destroy all the benefits of a probiotic), the vitamins (such as B vitamins and vitamin K), as well as short-chain fatty acids (SCFAs), such as butyrate, propionate, and acetate.7-9

The importance of short-chain fatty acids

The symbiotic relationship that exists between us and the trillions of beneficial species that live within our guts is immensely complex, but we are learning that a significant way these bacteria support human health is by way of the production of SCFAs.6,7 Butyrate, for example, is the preferred source of energy for the cells that line the large intestine, and exerts an anti-inflammatory effect in the gastrointestinal tract.5 Butyrate also promotes the health of the tight junctions in the intestinal tissue, whose integrity is vital to reducing the risk of increased intestinal permeability, also known as leaky gut.2,5,10,11 Butyrate also increases mucin production by goblet cells, which make up a protective mucous blanket that covers the gastrointestinal tract and is often the first to interact with invading pathogens to neutralize them.10–12

What happens when fiber is in short supply?

The Adequate Intake (AI) for fiber is 25-38 grams daily, and yet the average U.S. adult only consumes 12-18 grams per day.13 When dietary fiber is limited, the gut bacteria rely on proteins and fats as a food substrate; however, the result is that far fewer short-chain fatty acids are produced.8,14 Such changes in dietary fiber’s effects can be rapid and dramatic.14 For example, a 2013 clinical trial found that when the diet was shifted from a plant-based diet providing a minimum of 30 grams of fiber daily to a meat-based diet that was mostly devoid of fiber, significant changes were found in the types of bacteria present in the gut within just 24 hours, including reductions in microbial diversity and reductions in the fermented end products known as postbiotics.14 While this is not a critique of meat-based diets, it is an indication that fiber from plant carbohydrates plays an integral role in promoting the growth of beneficial bacterial strains and should be considered a staple part of our dietary habits and supplement regimens. 

For individuals who adhere to a paleo diet and think carbs are forbidden, ample evidence exists that our paleolithic hunter/gatherer ancestors survived on a wide variety of food sources, including grains, such as millet and oats.15 Most recently, a sandstone pestle used to grind oats into flour was discovered in an ancient cave in southern Italy dating back 33,000 years.15 

Conclusion

Because many of us might not be getting sufficient fiber from diet alone, supplementation is an excellent option to consider, and Thorne’s FiberMend formulation, containing soluble fiber and non-fiber prebiotics, dissolves easily in water and delivers a combination of ingredients clinically researched to enhance feelings of fullness, maintain a healthy blood sugar level, and promote regularity.*

Although it is always recommended to start with small amounts of fiber and gradually increase so your body can adjust to the change in intake, Thorne’s FiberMend is less likely to be accompanied by the symptoms of gas and bloating often seen with other prebiotic fiber blends. This is because the guar gum fiber has been partially predigested with enzymes. 

For those of you “minding your macros,” it’s important to note that fiber and resistant starch do not count toward your carbohydrate intake, although calculations for resistant starch are not as readily available as fiber.4 

There is no “one size fits all” approach when it comes to nutrition, and the consumption of carbohydrates should be personalized to your life stage, activity level, and personal health goals. However, plenty of evidence indicates we all could probably benefit from an increased intake of fiber and complex carbohydrates, so consider checking in with your gut before cutting these from your diet.

You can find the complete suite of probiotic supplements that Thorne offers here. And if you would like a comprehensive look at your own gut microbiome and the bugs living there, take the Thorne Gut Health Test, complete with an easy wipe for sample collection.

References

  1. Mul JD, Stanford KI, Hirshman MF, et al. Exercise and regulation of carbohydrate metabolism. In: Progress in Molecular Biology and Translational Science. Vol 135. Elsevier; 2015:17-37. doi:10.1016/bs.pmbts.2015.07.020
  2. Holscher HD. Dietary fiber and prebiotics and the gastrointestinal microbiota. Gut Microbes 2017;8(2):172-184. doi:10.1080/19490976.2017.1290756
  3. Slavin J. Fiber and prebiotics: Mechanisms and health benefits. Nutrients 2013;5(4):1417-1435. doi:10.3390/nu5041417
  4. DeMartino P, Cockburn DW. Resistant starch: impact on the gut microbiome and health. Curr Opin Biotechnol 2020;61:66-71. doi:10.1016/j.copbio.2019.10.008
  5. Oliphant K, Allen-Vercoe E. Macronutrient metabolism by the human gut microbiome: Major fermentation by-products and their impact on host health. Microbiome 2019;7:91. doi:10.1186/s40168-019-0704-8
  6. Scott KP, Duncan SH, Flint HJ. Dietary fibre and the gut microbiota. Nutr Bull 2008;33(3):201-211. doi:10.1111/j.1467-3010.2008.00706.x
  7. Vinderola G, Sanders ME, Salminen S. The concept of postbiotics. Foods 2022;11(8):1077. doi:10.3390/foods11081077
  8. Koh A, De Vadder F, Kovatcheva-Datchary P, et al. From dietary fiber to host physiology: Short-chain fatty acids as key bacterial metabolites. Cell 2016;165(6):1332-1345. doi:10.1016/j.cell.2016.05.041
  9. Huang FC, Huang SC. The combined beneficial effects of postbiotic butyrate on active vitamin D3-orchestrated innate immunity to salmonella colitis. Biomedicines 2021;9(10):1296. doi:10.3390/biomedicines9101296
  10. den Besten G, van Eunen K, Groen AK, et al. The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism. J Lipid Res 2013;54(9):2325-2340. doi:10.1194/jlr.R036012
  11. Ríos-Covián D, Ruas-Madiedo P, Margolles A, et al. Intestinal short-chain fatty acids and their link with diet and human health. Front Microbiol 2016;7. doi:10.3389/fmicb.2016.00185
  12. Kim JJ, Khan WI. Goblet cells and mucins: Role in innate defense in enteric infections. Pathogens 2013;2(1):55-70. doi:10.3390/pathogens2010055
  13. King DE, Mainous AG, Lambourne CA. Trends in dietary fiber intake in the United States, 1999-2008. J Acad Nutr Diet 2012;112(5):642-648. doi:10.1016/j.jand.2012.01.019
  14. David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature 2014;505(7484):559-563. doi:10.1038/nature12820
  15. Mariotti Lippi M, Foggi B, Aranguren B, et al. Multistep food plant processing at Grotta Paglicci (Southern Italy) around 32,600 cal B.P. Proc Natl Acad Sci 2015;112(39):12075-12080. doi:10.1073/pnas.1505213112
  16. Markowiak P, Śliżewska K. Effects of probiotics, prebiotics, and synbiotics on human   health. Nutrients 2017;9(9):1021. doi:10.3390/nu9091021