By now, word has spread, that refined sugar is not healthy for us. And even though sugar consumption has been shown to contribute to lifestyle diseases like obesity, heart disease, diabetes, non-alcoholic fatty liver and cavities, sugar is still everywhere and we eat way too much of it. [1-4]
In 2020/21, Germans consumed an average of 95 grams of sugar daily, adding up to 34,8 kg per person, per year  and the Americans get on average 17 teaspoons of added sugars each day!  An average-sized chocolate bar contains for example 6.5 teaspoons of sugar. The World Health Organization (WHO) recommends a daily sugar intake of around 25 grams (6 teaspoons) of household sugar. 
(I wrote this article for MyMicrobiome.info and publish it here with kind permission of MyMicrobiome.)
How sugar affects the microbiome
A large part of our Western diet consists of heavily processed foods with high amounts of sugars, that alter the gut microbiome. [8, 9] Some sugars are already being processed in the small intestine. Others however, make it down to the large intestine, where they feed the “bad” bacteria, helping them to proliferate and crowd out the “good” ones.
In contrast, complex polysaccharides – better known as “fiber” – are not being digested in the small intestine. These microbiota-accessible carbohydrates (MACs) travel to the large intestine, where they feed, and thereby support, beneficial microbes.
The problem is, that the Western diet is very low in fiber. Meaning, the good microbes don’t get enough energy to produce essential compounds like vitamins, amino acids and short-chain fatty acids (SCFAs) like butyrate, acetate and propionate that promotes gut and brain health by lessening inflammation and protecting the gut lining. [10, 11]
A low-MAC diet decreases microbial diversity,  which can result in a dysbiosis that might lead to “leaky gut”. A condition that allows harmful substances to pass through the hyperpermeable wall of the intestine. When they reach the bloodstream, they can trigger an inflammatory response and disease processes.
How to support the good microbes
Fiber-rich diets promote the growth of microbes that break down dietary fiber and metabolize it into SCFAs. Like the species Bacteroides thetaiotaomicron, that is associated with lean and healthy individuals.  Fiber has also been shown to help with constipation, Irritable Bowel Syndrome , Crohn's disease  and weight loss.
The more fiber from whole foods like berries, apples, bananas, avocados, carrots, cruciferous vegetables, oats, legumes and psyllium we add to our diet, the more we support the microbes that support us. Small word of caution: Depending on the state of the microbiome, fiber intake should be increased slowly, as it might initially cause gas production and bloating.
When we recognize the negative impact that sugar has on our tiny friends, it gets easier to say no to sugary temptations. So, the next time you are faced with the decision to go with the cookie or the carrot, think about which microbes you want to feed…
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