I recently wrote about the relationship between sleep and inflammation. Both sleep and inflammation are regulated by our circadian biorhythms. When one goes awry, the other is likely to suffer, also. Sleeping poorly, including getting too little or too much sleep—increases the chronic, low-grade inflammation that is a significant contributor to disease.
Systemic inflammation, in turn, can also undermine healthy sleep. How? By triggering physical and psychological changes that make it harder to get a good night’s rest. Inflammation comes with the presence of cytokines, chemical messengers that have been shown to regulate sleep. Elevated cytokines have been linked to trouble sleeping and to insomnia. Inflammation can create pain and stiffness in the body that make it difficult to fall asleep and sleep soundly. (Physical pain is a common factor in insomnia and other sleep problems.) Inflammation involves higher levels of cortisol, a hormone that stimulates alertness and can contribute to feelings of psychological stress. Stress is among the most significant common obstacles to healthy sleep.
Diets high in sugar increase chronic inflammation. Sugar contributes to the formation of harmful biochemical compounds that spike inflammation. Sugar and refined carbohydrates cause unhealthful, inflammation-boosting changes to gut bacteria—now recognized as a key regulator of overall health. Sugar in our diets also elevates cholesterol, which is linked to increased inflammation.
Sugar hurts a healthy gut
You’ve heard me talk before about the complex relationship between sleep and gut health. Our gut microbiome is the vast community of microscopic organisms living our intestines. Our gut microbiome has a nervous system, produces neurotransmitters and hormones (including the sleep hormone melatonin). Like sleep, our microbiome is regulated by circadian rhythms. We’re still just beginning to understand how gut microbiota affects our health and contributes to aging and disease. But this densely populated microbiotic community appears to have a significant influence over our metabolism, immune health, cardiovascular and circulatory function, as well as mood. We have yet to see definitive research, but there are indications that the gut microbiome also may play an important role in sleep.
The research on sugar’s effects on the gut microbiome is surprisingly limited. There’s an abundance of evidence that a standard Western diet—one that’s high in processed sugars and fats—causes unhealthful changes to the composition of our gut microbiota, and to the strength of the intestinal wall that contains this collection of microorganisms, and keeps them from entering the bloodstream, where they can cause inflammation and other damage to healthy functioning.
But it is difficult to extract from this research the specific effects of sugar on gut health. We’re only now beginning to see a handful of studies investigating sugar’s effects on the microbiome. A 2018 study found that dietary fructose—a simple sugar found naturally in fruits and juices and also found in processed sweeteners including table sugar and high-fructose corn syrup—causes changes to the microbial make-up of the gut. There’s also a very interesting 2017 study conducted in rats, which showed that consumption of added sugars in childhood and adolescence led to alterations to the gut microbiome. In this study, scientists were able to isolate and attribute the specific effects of sugar, apart from other factors such as caloric intake and body fat, which also affect gut microbiota. It’s great to see new research exploring the effects of sugars on microbiotic health—we need to see much more.
There are other ways sugar may indirectly affect our gut health. Sugar contributes to inflammation, and inflammation is harmful to the diversity and function of gut bacteria. A diet that includes frequent consumption of added sugars is likely to lead to weight gain. Studies show that dietary-induced obesity creates changes to the microbial life in our gut. People who get calories from sugary foods may also be consuming less healthful nutrients, including fiber, from whole, unprocessed, no-sugar-added food sources.
Fiber is food for the bacteria and other microbes in our intestines. Eating plenty of fiber is one way to keep our gut healthy. One recent study in mice showed the dramatic effects of switching to a low-fiber diet from a high-fiber one. A low-fiber diet produced significant changes to the diversity of bacterial life in the microbiome. The mice developed inflammation, and their blood sugar levels rose. The intestinal barrier that holds bacteria within the gut weakened. Greater intestinal permeability—sometimes called “leaky gut”—is associated with inflammation and disease.