“Imagine our gut as being a garden with flowers, grass and weeds,” says Jacob Wilson, PhD, CSCS, author of The Ketogenic Bible and member of The Vitamin Shoppe Wellness Council. “The gut microbiome contains a garden with good bacteria that helps our body, and bad bacteria that cause inflammation and hunger," he says. "Sugar selectively feeds the bad bacteria. This means you end up having more weeds than flowers.” (Weeds, in this analogy, meaning bad bacteria.)
We all know that sugar is enemy number one of the health world, but how freaked should we be about its effect on our gut? Experts share what you need to know.
What we know about sugar and gut health
Your gut microbiome is constantly at work to maintain good digestive health—or, you know, keep the grass green and flowers blooming. “Good bacteria in our gut lower inflammation, make us happy, lean, and give us longevity," he says. Indeed, a flourishing digestive microbiome has been associated with better mental health (possibly because the bacteria in the gut appear to communicate with certain receptors and gene regulators in the brain), among other important health outcomes.
But an abundance of "bad" bacteria in the gut, Dr. Wilson argues, can lead to inflammation, digestive upset, acne, and other health issues. And sugar—particularly highly refined, added sugars—feeds the bad stuff, helping them flourish, he says. That's an issue for most of us, since the standard American diet is loaded with sugar. The American Heart Association’s daily recommendation for added sugars is no more than six teaspoons aka 25 grams a day for women, yet the U.S. Department of Health dietary guidelines says that the average American takes in a whopping 17 teaspoons of added sugar per day.
This theory about sugar and gut health has been supported by promising new research. A 2017 study from Frontiers in Behavioral Neuroscience found that consuming a standard Western diet high in processed sugar and saturated fats alters gut flora, which is associated with an impaired hippocampus, the part of your brain that's associated with memory and emotions. A 2018 study suggested that eating lots of fructose (a form of sugar) suppressed the growth of beneficial gut bacteria in mice.
However, the International Food Information Council Foundation notes that most human studies tracking the relationship between sugar and gut health (like these ones) have been analyzed through the lens of the standard American diet as a whole, and thus it’s difficult to determine which negative outcomes are a result of high sugar or high saturated fat. There have also been very few randomized clinical trials on humans on this subject, which is the gold standard of research—and thus most of these findings are promising but preliminary.
Understanding the differences between sugar sources
Before you start slashing all sugar from your diet for the sake of better gut health, remember that certain forms of sugar (like the natural kind you get from fruit) are still worth consuming in moderation. “When you eat things like fruit, you have so many nutrients and fibers that actually improve gut health that you have an overall positive effect,” says Dr. Wilson. “It’s the consumption of refined sugars in the absence of their natural forms that cause problems.”
That's why it's generally not advised to cut out naturally occurring sugars unless you have fructose intolerance or fructose malabsorption. These conditions might lead to digestive disturbances like gas, bloating, and abdominal pain, says Patricia Bannan, RDN, author of Eat Right When Time is Tight, so if you notice any of these symptoms, talk to a doctor about it.
Other naturally-occurring sugars are still worth consuming mindfully. Bannan says there’s not enough definitive research to suggest natural sweeteners like honey, maple syrup, and agave influence your gut microbiome any differently than processed sugar. (And in terms of nutrition, they should be usually treated like added sugar.) However, she notes that honey provides trace amounts of vitamins and minerals, which in and of themselves can have positive effects on gut flora.
Similarly, artificial sweeteners are a tricky subject when it comes to gut health. They're sugarless (and useful for diabetics and other people who need to closely monitor sugar intake), but their use has been linked to a host of chronic diseases as well as potential gut health problems. A 2018 study found that six different types of artificial sweeteners were toxic to certain strains of bacteria found in the digestive system. A mouse study from the medical journal Nature also suggested that common sweeteners like saccharin, sucralose, and aspartame could induce glucose intolerance by altering the composition of gut microbiota. However, Bannan says while preliminary studies have suggested a relationship between different sweeteners and gut health, most have been conducted on mice or in test tubes, and thus can't be definitively applied to human health on a larger scale.
Finding a sweet spot for gut health
Again, no one's over here saying you can't eat any sugar anymore. (What's life without the occasional cookie?) But you can make small lifestyle changes to counteract some of sugar’s potential effects on your microbiome. Bannan suggests balancing your consumption of foods higher in sugar with ones rich in fiber—like whole grains, fruits, and vegetables—as well as healthy fats from nuts, seeds, and avocados.
Additionally, Bannan says staying hydrated can also help regulate digestion and stabilize energy levels. It's also a good idea to increase intake of fermented foods like kimchi, kefir, and sauerkraut, which are high in live probiotics that colonize in the gastrointestinal tract and regulate gut flora.
Yes, some probiotic- and prebiotic-rich foods contain sugar—but no, consuming them won’t negate your gut health efforts. “I think the main problem with sugar is consuming it in a pure refined format,” says Dr. Wilson. “Greek strains of yogurt are relatively low in sugar and high in probiotics and prebiotics," he says as an example—both of which are important for maintaining a healthy digestive system.
Ultimately, Bannan says most healthy adults should be just fine sticking with American Heart Association’s daily sugar limit recommendations. “The one exception to this is if you have pre-diabetes or diabetes,” she says. “[In these cases] artificial sweeteners and stevia are preferable to real sugar, but it’s still important to keep the amount in check.” Regardless of potential gut health implications, it's always a good idea to be mindful when eating the sweet stuff.
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