by Craig Weatherby
Want to help ensure that the good bugs outnumber the bad in your belly?
New findings suggest it makes sense to cozy up with some cocoa, or enjoy a bit of extra dark chocolate.
In a preliminary clinical trial, people who drank a beverage rich in cocoa-derived antioxidants enjoyed a significant increase in their gut levels of beneficial bacteria.
Better yet, this increase was accompanied by reductions in a microbe associated with diarrhea and constipation (clostridia), and in blood levels of cholesterol, triglycerides, and C-reactive protein (CRP)… a marker of inflammation linked to heart risks.
The study, which was conducted by researchers from the UK’s Reading University and chocolate giant Mars, Inc., is the first to demonstrate that cocoa flavanols can boost the numbers of beneficial bacteria in people’s guts.
Before we delve into the details, let’s review the research on the role of intestinal microbe colonies in human health.
Probiotics and prebiotics: A quick primer
People’s gastrointestinal tracts play host to many millions of microbes, most of which are either neutral or beneficial.
Some, such as lactobacilli and bifidobacteria, seem virtually essential to immunity and overall health.
A healthy gut ecosystem is one in which beneficial micro-organisms greatly outnumber potentially harmful bugs. The opposite, unhealthful balance is referred to as “dysbiosis”.
The most critical microbial colonies occur in the colon, where, as the authors of a recent evidence review wrote, “…a true symbiosis [between probiotic microbes and] the host [person] exists that is a key for well-being and health” (Roberfroid M et al. 2010).
Thanks to many human studies, it’s clear that certain foods or food factors can change the microbial composition of the gut in significant, beneficial ways.
“Probiotic” foods such as yogurt and fermented vegetables with active cultures contain the same beneficial microbes found in the human gut—mostly lactobacilli and bifidobacteria—and eating these cultured foods appears to support immune health by keeping gut-based pathogens in check.
(Doctors often prescribe lactobacilli supplements to patients taking antibiotic drugs, which kill these beneficial bacteria along with pathogenic microbes.)
In contrast, “prebiotic” food factors bring intestinal benefits indirectly, by serving as food for lactobacilli and other beneficial bacteria.
Prebiotics are defined as “non-digestible (by the host) food ingredients that have a beneficial effect through their selective metabolism in the intestinal tract” (Gibson GR et al. 2004).
As the authors of the same evidence review put it, “…the prebiotic effect [of certain food factors] is now a well-established scientific fact” (Roberfroid M et al. 2010).
The chief prebiotic supplements are three plant fibers called inulin, galactooligosaccharides (GOS), and fructooligosaccharides (FOS), which are found in or derived from Jerusalem artichoke root, chicory root, burdock root, and beets.
Clinical study detects prebiotic potential from cocoa compound
Last year, the authors of a Nestle-funded human study reported that daily consumption of 40 grams (1.4 ounces) of dark chocolate lowered levels of stress-related hormones (cortisol) and neurotransmitters in participants diagnosed with anxiety.
Those changes were linked to changes the composition of their microbial gut colonies.
As they described the implications of their findings, “…subtle changes in dietary habits, such as eating dark chocolate, can benefit both host and microflora metabolism with potential long term health benefits” (Rezzi S 2010).
Now, findings from the UK-Mars study suggest that cocoa flavanols may rival the prebiotic effects produced by fructooligosaccharides (FOS), which serve as popular prebiotic supplements.
The small but rigorously designed new study was a randomized, double-blind, crossover, controlled clinical trial, led by the University of Reading’s Jeremy Spencer, Ph.D., and sponsored by Mars, Inc. (Tzounis X et al. 2010).
For the trial, 21 healthy adults were divided into two groups, with each group assigned to consume a different flavanol-supplemented beverage daily:
Low-flavanol beverage providing 23mg of cocoa flavanols
High-flavanol beverage providing 494mg of cocoa flavanols
The trial began with both groups drinking their assigned beverage daily for four weeks, followed by a four-week “wash-out” period during which they drank neither flavanol-supplemented beverage.
The two groups then switched beverages for a further four weeks of daily consumption.
Compared with the low-flavanol drink, participants showed significant increases in their gut levels of beneficial bifidobacteria and lactobacilli when they were drinking the high-flavanol beverage.
These increases in beneficial microbes were accompanied by reductions in blood levels of cholesterol, triglycerides, and CRP… a marker of inflammation linked to heart health.
As the authors wrote, “The increase in the growth of Lactobacillus spp. in response to cocoa flavanols is of note because this bacterial group is associated with beneficial effects in the gut, including an ability to prevent the growth of pathogenic organisms, and most currently accepted prebiotics [e.g., FOS] do not elicit changes [increases] in lactobacilli” (Tzounis X et al. 2010).
The researchers noted that higher gut levels of bifidobacteria are “strongly associated with positive effects in the large intestine, thanks to the ability of bifidobacteria to inhibit the growth of pathogens, drive the synthesis of certain vitamins (e.g., vitamin B-9), and reduce plasma [blood] cholesterol levels” (Tzounis X et al. 2010).
And the researchers noted that, in comparison with two prebiotic food fibers—fructooligosaccharides (FOS) and galactooligosaccharides (GOS)—the cocoa flavanols produced similarly substantial effects at a much lower dose.
While encouraging, these findings will need to be repeated in a larger trial and do not justify eating copious amounts of dark chocolate in an attempt to correct medically diagnosed dysbiosis.
But they suggest the existence of another, previously overlooked health benefit from the catechin-type polyphenols that abound in cocoa and tea.
Are cocoa flavanols antioxidants or gene-tweakers?
Most research into the potential benefits of cocoa relates to possible cardiovascular benefits of the flavanols found in cocoa.
And recent evidence reviews conclude that while much more research is needed, we have ample evidence that cocoa flavanols enhance vascular health in several ways (Corti R et al. 2009; Mulvihill EE et al. 2010; Ostertag LM et al. 2010; Rimbach G et al. 2009).
The flavanols in cocoa, tea, and berries are commonly referred to “antioxidants”, because they display potent free-radical-squelching effects in test-tube experiments.
However, like other polyphenol compounds in plant foods, it’s increasingly apparent that flavanols exert their beneficial effects through “nutrigenomic” influences on gene switches in our cells… rather than through direct, substantial antioxidant effects in the body (Scheid L et al. 2010).
The most promising cocoa compounds are procyanidins, which are also found in berries and grapes—and catechins (flavan-3-ols), which also occur in green tea.
Corti R, Flammer AJ, Hollenberg NK, Lüscher TF. Cocoa and cardiovascular health. Circulation. 2009 Mar 17;119(10):1433-41. Review.
Gibson GR, Probert HM, Loo JV, Rastall RA, Roberfroid MB. Dietary modulation of the human colonic microbiota: updating the concept of prebiotics. Nutr Res Rev. 2004 Dec;17(2):259-75.
Martin FP, Rezzi S, Peré-Trepat E, Kamlage B, Collino S, Leibold E, Kastler J, Rein D, Fay LB, Kochhar S. Metabolic effects of dark chocolate consumption on energy, gut microbiota, and stress-related metabolism in free-living subjects. J Proteome Res. 2009 Dec;8(12):5568-79
Mulvihill EE, Huff MW. Antiatherogenic properties of flavonoids: implications for cardiovascular health. Can J Cardiol. 2010 Mar;26 Suppl A:17A-21A. Review.
Ostertag LM, O'Kennedy N, Kroon PA, Duthie GG, de Roos B. Impact of dietary polyphenols on human platelet function--a critical review of controlled dietary intervention studies. Mol Nutr Food Res. 2010 Jan;54(1):60-81. Review.
Rezzi S. Email correspondence with NutraIngredients, February 2010.
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Roberfroid M, Gibson GR, Hoyles L, McCartney AL, Rastall R, Rowland I, Wolvers D, Watzl B, Szajewska H, Stahl B, Guarner F, Respondek F, Whelan K, Coxam V, Davicco MJ, Léotoing L, Wittrant Y, Delzenne NM, Cani PD, Neyrinck AM, Meheust A. Prebiotic effects: metabolic and health benefits. Br J Nutr. 2010 Aug;104 Suppl 2:S1-63. Review.
Scheid L, Reusch A, Stehle P, Ellinger S. Antioxidant effects of cocoa and cocoa products ex vivo and in vivo: is there evidence from controlled intervention studies? Curr Opin Clin Nutr Metab Care. 2010 Nov;13(6):737-42.
Tzounis X, Rodriguez-Mateos A, Vulevic J, Gibson GR, Kwik-Uribe C, Spencer JP. Prebiotic evaluation of cocoa-derived flavanols in healthy humans by using a randomized, controlled, double-blind, crossover intervention study. Am J Clin Nutr. 2011 Jan;93(1):62-72. Epub 2010 Nov 10.