How Disordered Eating Affects Digestion: Understanding Your Body
Disclaimer: This is not medical advice. The content in this blog is for informational purposes only.
This blog explains why digestive issues are so closely linked to chronic dieting, disordered eating, and eating disorders. Common questions I hear from clients are: Why does my stomach hurt after I eat? Do I have IBS? Do I have a food intolerance? Should I try the low FODMAP diet? If this sounds like you, read on.
Your digestive system requires a harmonious balance of enzymes/secretions, fluid-electrolyte balance, hormones (i.e. insulin), gut bacteria, and healthy intestinal villi. It also requires an enormous amount of energy to support these intricate processes and the mechanical aspects of digestion; churning and squeezing your food to move it along the entire gastrointestinal (GI) tract. There is a high risk for malnutrition in individuals engaging in chronic dieting, disordered eating, and eating disorders. Malnutrition has many negative health consequences, including digestion disruptions, which are described in detail below.
Chemical Digestion
Malnutrition often causes a reduction in digestive enzymes, which are needed to break down and absorb food properly. For example, there may be a reduction in lipase, the enzyme needed to digest fat, and lactase, the enzyme needed to digest dairy products, resulting in unpleasant GI side effects when these foods are consumed. This is a temporary intolerance that can be resolved with adequate nutritional intake.
When you are undereating or limiting the types of food you eat, your microbiome may be thrown off balance. Your microbiome refers to the colony of microbes residing in your gut. These microbes play a significant role in your health. A healthy microbiome requires enough nutrients and diverse food intake to feed the "good" bacteria. A reduction in digestive enzymes, bile, gastric acid, and other chemical networks can also disrupt the balance of your microbiome. When good bacteria are reduced, it allows the overgrowth of less favorable microbes in your gut causing many health issues and digestion disturbances.
Mechanical Digestion
Malnutrition may cause structural damage to the microvilli in the intestinal wall, resulting in absorption issues, nutrient deficiencies, diarrhea, and other GI discomfort. Additionally, your entire digestive system slows when you are not eating enough to support your body’s needs. Your stomach takes longer to empty food into your intestines and the rhythmic movements of your intestinal walls are slower, taking longer to pass food along. As you begin the refeeding process you may experience acid reflux, from delayed stomach emptying, gas, bloating, abdominal pain, and constipation, from a slowed GI tract. These uncomfortable side effects are temporary until your digestion system repairs itself.
Food Restriction
When you limit specific foods for a long time, your body must relearn how to metabolize the restricted foods, through gradual reintroduction. Many clients with long lists of “food intolerances”, are surprised to learn their bodies can handle these foods without symptoms when they begin healing. Almost everyone with disordered eating has a digestive issue. Without identifying the disordered eating piece it's easy to assume food intolerances or IBS are to blame. Trying something like the low FODMAP diet for IBS treatment will NOT solve the issue if IBS is not the cause of your digestion distress. It may make matters worse by further limiting food diversity. The good news is that digestive issues caused by disordered eating are reversible as you provide your body with adequate nutrition consistently. If you relate to these symptoms and feel like disordered eating could be the cause, reach out to a doctor and a registered dietitian with eating disorder expirience.
Written by: Mackenzie Michalczuk, RD, CDE
References
Chung, S. H., & Zhang, H. (2021). Starvation and its effects on the gut. Advances in Nutrition, 12(1), 1–10. https://doi.org/10.1093/advances/nmaa135
Geyra, A., Uni, Z., & Sklan, D. (2001). The effect of starvation on the small intestinal epithelium and disaccharidase activity in the young rat. Digestive Diseases and Sciences, 46(7), 1430–1437. https://doi.org/10.1023/A:1010654707986
Jones, K. D., Hübscher, S. G., & Mpabanzi, L. (2025). Gastrointestinal changes in paediatric malnutrition that may impact nutrition choice. Journal of Paediatric Gastroenterology and Nutrition, 80(2), 250–260.
Kaur, H., Gupta, M., & Singh, A. (2025). Malnutrition and its influence on gut sIgA–microbiota dynamics: A comprehensive review. Nutrients, 17(4), 1125. https://doi.org/10.3390/nu17041125
Mehler, P. S., Winkelman, A. B., Andersen, D. M., & Gaudiani, J. L. (2010). Nutritional rehabilitation: practical guidelines for refeeding the anorectic patient. Journal of nutrition and metabolism, 2010.
Sato, Y., & Fukudo, S. (2015). Gastrointestinal symptoms and disorders in patients with eating disorders. Clinical journal of gastroenterology, 8, 255-263.
Subramanian, S., Mahowald, M. A., & Gordon, J. I. (2024). Uncovering the complexity of childhood undernutrition through strain-level analysis of the gut microbiome. BMC Microbiology, 24, 211. https://doi.org/10.1186/s12866-024-03211-w
Tremaroli, V., & Bäckhed, F. (2012). Functional interactions between the gut microbiota and host metabolism. Nature, 489, 242–249. https://doi.org/10.1038/nature11552