Written by Dr. Nicole Avena
Dr. Avena is a professor, research neuroscientist, and author on food & addiction. She has done extensive research on sugar and the effects it can have on health. She is the author of Sugarless: A 7 Step Plan to Uncover Hidden Sugars, Curb Your Cravings and Conquer Your Addiction.
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The gut, often referred to as the body’s "second brain," is more than just a digestive system—it's a complex ecosystem that plays a crucial role in our overall health. Composed of the gastrointestinal (GI) tract, the gut is home to trillions of microorganisms, collectively known as the gut microbiome. A healthy gut microbiome thrives on nutritionally diverse foods, and diets high in added sugars can disrupt the gut, increasing inflammation and gut-related health issues. Understanding how diet impacts the gut microbiome is essential for optimizing digestion, immune function, and overall well-being.
What is The Gut?
The “gut” is a term commonly used to refer to the body’s GI tract. The gut microbiome encompasses the entire microbial community that exists within the GI tract.(1) The microbiome is a complex community of trillions of microorganisms, including bacteria, fungi, and viruses, that live in the digestive tract and play essential roles in digestion, immunity, and overall health. It plays a large role in digesting and absorbing the nutrients that we obtain through the foods we eat. Our gut helps to eliminate toxins and waste, while also supporting energy production.
There is also the gut-brain connection, which refers to the complex communication network between the gut and the brain, involving nerves, hormones, and immune factors. Research suggests that gut health can significantly influence mood, cognitive function, and even stress levels. This bidirectional relationship means that a balanced gut microbiome may support mental well-being, while stress or anxiety can impact gut health in return.
Impact of Food on The Gut
The foods we eat provide essential nutrients for the body, as well as for the microbial flora in our gut. For example, indigestible carbohydrates, also known as dietary fiber, can be found in nuts, whole grains and fruits, and produce short-chain fatty acids which are considered to be beneficial for gut health in the average adult.
To maintain a healthy gut, the focus should be on eating a diverse, nutritionally balanced diet, because this helps develop a diverse bacterial community within the gut. Unfortunately, the typical American diet tends to be unbalanced, which leads to poorer gut health due to a less diverse microbiome.
Sugar and Gut Health
As the foods we eat can positively or negatively impact our gut health, it is important to consider sugar’s role in our gut microbiome. Some research has been conducted associating a high-sugar diet with disruptions in gut health.(2) Excessive added sugar intake and hyperglycemia (high blood sugar) have both been shown to disrupt the intestinal barrier of the GI tract.(3) Whenever the intestinal barrier becomes disrupted, gut permeability (leaky gut) is increased, which can lead to a disturbance in mucosal immunity—increasing susceptibility to infection.(3)
Sugar and Inflammation
Natural sugars, found in whole foods like fruits and vegetables, come with fiber, vitamins, and minerals that help slow sugar absorption, supporting stable blood sugar and gut health. Added sugars, often found in many processed foods, can disrupt the gut microbiome and potentially lead to inflammation, which may worsen digestive and overall health if consumed in excess. Inflammation in the gut can have far-reaching effects on the body, impacting everything from digestion, to mood, and skin health. When the gut is inflamed, it may lead to digestive issues like bloating, discomfort, or irregular bowel movements. This inflammation also affects the gut-brain axis, which can lead to mood swings, increased feelings of anxiousness, and even feeling blue or down. Additionally, gut inflammation has been linked to skin issues such as acne or eczema, as an imbalanced gut microbiome can impact overall immune function and skin health.
Added Sugar Recommendations
We understand that too much added sugar is not ideal for gut health; however, it is also important to understand how much is “too much.” Due to the growing body of evidence supporting the negative implications of added sugar on overall health, the American Heart Association recommends limiting your intake of added sugar to no more than 9 teaspoons (36 grams or 150 calories) of added sugar per day for men, and no more than 6 teaspoons (25 grams or 100 calories) per day for women.(4) The World Health Organization suggests reducing your intake of added sugar even further to <5% for even greater health outcomes.(3)
Fueling a Healthier Gut
Fueling a healthier gut starts with the foods we choose to put into our bodies. Aside from limiting our added sugar intake, there are other ways to optimize your diet to promote gut health. Incorporating both probiotics and prebiotics into the diet can help to nourish your gut. Probiotics are living microorganisms found within fermented foods—like saurkraut, yogurt and Keifer—that add to your gut microbiota. We can think of prebiotics as fuel for probiotics as they help the microorganisms grow and obtain optimal health. Examples of prebiotics include onion, garlic, beans, oats, and apples. The key to gut health is promoting a diverse microbiota, so it is best to focus on consuming a diverse, highly nutritious diet and limiting added sugar intake.(5)
References
1. Zhang P. Influence of Foods and Nutrition on the Gut Microbiome and Implications for Intestinal Health. Int J Mol Sci. 2022;23(17):9588. Published 2022 Aug 24. doi:10.3390/ijms23179588.
2. Fajstova A, Galanova N, Coufal S, et al. Diet Rich in Simple Sugars Promotes Pro-Inflammatory Response via Gut Microbiota Alteration and TLR4 Signaling. Cells. 2020;9(12):2701. Published 2020 Dec 16. doi:10.3390/cells9122701
3. Arnone D, Chabot C, Heba AC, et al. Sugars and Gastrointestinal Health. Clin Gastroenterol Hepatol. 2022;20(9):1912-1924.e7. doi:10.1016/j.cgh.2021.12.011
4.American Heart Association. How Much Sugar is Too Much? How Much Sugar Is Too Much? | American Heart Association/Accessed 10/27/24.
5. Harvard Health. Feed Your Gut. Health.harvard.edu. Published April 6, 2023. Accessed October 2024. https://www.health.harvard.edu/staying-healthy/feed-your-gut