Last week, I touched on the outcomes of RED-S on metabolic rate. Click here if you missed that blog. This week, I’ll touch on one of the less talked about outcomes of RED-S, gastrointestinal (GI) function such as bloating, nausea, gas, constipation and/or diarrhea.

Altered GI function can be the result of the reduced metabolic rate seen with RED-S. As I touched on last week, when too few calories are consumed the body acts to conserve energy. One of the ways it can do this is by spending less calories on digesting food. This results in slowed movement of food through the GI tract. This slowed movement leads to symptoms such as gas, bloating and/or constipation.

Athlete’s restricting their energy intake may also be eating large amounts foods that can cause GI symptoms. This includes excessive intake of foods that contain sugar alcohols (gum, sugar free candies etc.) and caffeine (coffee, diet pop etc). These foods can have a laxative effect leading to diarrhea or loose stools. Athletes restricting energy intake may also fill up on low calorie foods such as vegetables and fruits that are high in fibre. These foods are hard to digest and if consumed in large quantities, can also cause GI symptoms such as gas, bloating and/or diarrhea.

Unfortunately, these GI symptoms can often make it hard for athletes with RED-S to increase their calorie intake. This in turn perpetuates the problem as food intake continues to be restricted. In other situations, athletes are falsely diagnosed with food intolerances or allergies when in fact, undereating is the culprit. For instance, an athlete may believe gluten or lactose is contributing to their gas or bloating and cut these foods out of their diet. As a result, nutritious foods are unnecessarily eliminated when they are not actually causing the GI symptoms.

RED-S has many negative health outcomes. Altered GI function being one of them. Gas, bloating, constipation, and/or diarrhea could be another sign of under-fuelling. Working with a Registered Dietitian can help with symptom management so that both energy intake and GI function can be restored.

Categories: Megan Kuikman

Megan Kuikman

Hello! I’m Megan Kuikman. I’m a Registered Dietitian with specialized training in sports nutrition. My goal is to help athletes and active individuals achieve a healthy attitude towards health, training, and food. I empower athletes to fuel properly for training in order to restore their health and enhance performance. You can get in touch with me at:


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