They make up about 95% of the cells in our bodies, play an important role in food digestion, produce vitamins, and help fight infection and disease – yes, life would be very different without gut bacteria.
And, like in your average fairy tale, it is a case of good triumphing over evil as the gut ‘microbiota’ have pathogenic properties in addition to their health-giving ones: they can produce toxins and carcinogens, cause infections and have been implicated in conditions including diabetes and obesity, inflammatory bowel disease and cancer.
Copyright: iStockPhoto Thinkstock 2011
Balance, therefore, is key to a healthy gut. In recent years there has been growing interest in both probiotics (live microorganisms that are added to foods such as yogurts) and prebiotics (non-digestible food ingredients that stimulate the growth or activity of certain bacterial species) as a way to alter the gut microbiota to a more healthy composition.
Most of the prebiotics on the market are long-chain carbohydrates (fructooligosaccarides and galactooligosaccharides), but scientists and food manufacturers are on the lookout for other potential beneficial supplements that may stimulate the microbiota in different ways.
Dr Jeremy Spencer at the University of Reading is leading a research project, funded through the BBSRC’s Diet and Health Research Industry Club (DRINC), to examine the impacts of industrial processing on the levels of flavanols in foods such as cocoa and coffee.
“We know that some flavanols in cocoa, such as epicatechin, are absorbed in the small intestine and studies have shown that these compounds have direct benefits for cardiovascular health,” says Spencer. “But the majority of flavanols in pure cocoa are not absorbed. Instead they pass to the large intestine where, we believe, they may influence the growth of the microbiota. Yet there has been very little research regarding the ability of these flavanols or other phytochemicals to influence the growth of beneficial intestinal bacteria to date.”
Drink to your health
In a randomised, controlled, double-blind trial, Spencer and colleagues examined the effects of a drink containing either high or low levels of cocoa flavanols on the gut microbiota of healthy human volunteers. They found that the populations of beneficial bacteria in the gut (bifidobacteria and lactobacilli) increased, and potentially harmful populations of clostridia bacteria decreased in the participants who consumed the high flavanol drink, compared to volunteers in the low flavanol group.
It’s the first time that the consumption of cocoa flavanols has been shown to have a potential prebiotic effect.
“We were particularly pleased to observe the increase in growth of Lactobacillus species in response to cocoa flavanols,” says Spencer. “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 do not elicit changes in lactobacilli.”
According to Spencer, Lactobacilli may be better equipped to use flavanols as an energy source compared to their bacterial competitors in the gut.
The team also observed that the high flavanol drink led to a significant decease in a group of clostridia bacteria that includes Clostridium perfringens, a known pathogen that has been implicated in the progression of colon cancer and the onset of inflammatory bowel disease.
The benefit’s in the bean
But before rushing home to guzzle a nice hot cup of cocoa, it’s worth pointing out that the concentration of flavanols in processed cocoa is much lower than the pure cocoa extracts tested in this study.
Copyright: iStockPhoto Thinkstock 2011
As part of his wider DRINC-funded project, Spencer is looking at the broader health benefits of flavanols, and is working with manufacturers to identify ways to optimise processing to prevent flavanol loss. This is because conventional processing (drying, fermentation, roasting and alkaline treatment) drastically reduces the amount of flavanols – up to 98% in the case of epicatechin (ref 1).
“Ultimately, our goal is to develop future strategies to maximise flavanols in our foods, whether by optimising industrial processing conditions or extracting the active ingredients that can be added to other foods or used as supplements,” says Spencer.
But interestingly, the team has discovered that whilst the roasting of cocoa does lead to flavanol losses, it does not significantly reduce the prebiotic effect.
Spencer believes that this is because, during roasting, flavanols participate in ‘Maillard reactions’, forming new complexes which also promote the growth of ‘good bacteria’. Such chemistry has long been known to be important for flavour and aroma development in cocoa but now it seems that these bi-products may also contribute to beneficial effects in our gut.
“We observed a prebiotic effect with just 500mg of flavanols in our study. The news for flavanols is now particularly good because as well as the cardiovascular benefits we also have a prebiotic effect at amounts that are achievable through a moderate dietary intake of cocoa, apples, red wine and green tea,” says Spencer.
X. Tzounis et al., Prebiotic evaluation of cocoa-derived flavanols in healthy humans by using a randomised, controlled, double-blind, crossover intervention study. Am. J. Clin. Nutr. 2011
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