There are several scenarios in which athletes do things that may appear unhealthy to an "outsider" in order to keep the body in good health. For example, someone who exercises 60-minutes a day does not require 200+ calories to fuel the workout. But an athlete preparing for a 4-hour ride will plan for at least 60g of carbohydrates per hour in the form of sport nutrition to prolong endurance capacity.
Another scenario athletes apply is drastically reducing fiber-rich foods (like vegetables) in the 24-72 hours prior to an endurance event.
If you've ever had an upset stomach, you have a gastrointestinal condition such as Crohn's or diverticulitis or prepared for a colonoscopy, there's a good chance you understand the purpose (and benefits) of a temporarily limiting dietary fiber.
Before discussing the benefits of a low residue diet, first it's important to understand how poop is made.
The digestive system includes the liver, pancreas, gallbladder and gastrointestinal (GI) tract. The GI tract is a connection of organs - mouth, esophagus, stomach, small intestines, large intestines, anus.
The food you eat goes on an incredible ride through your body - from your mouth to your anus. The purpose of the digestive system is to turn food into nutritients and energy. This is a very important process because the food we eat and the liquids we drink keep us healthy and help our body function properly. Anything left over is turned into waste (or stool) and is then disposed of as a bowel movement.
The digestive system moves food through the intestines, which can take between 24-72 hours. After food goes through the stomach, food passes from one area of the intestines to the next. Food stays in certain areas for a specific amount of time so the gut can do what it needs to do - absorb nutrients, absorb fluids, process waste, expel waste.
When food is passed from the small intestines to the large intestines (colon), much of the liquid has been removed and it is now of soft consistency. The colon can now store, process and get rid of waste. The colon hosts a large population of bacteria, which help break down undigested food and neutralize some of the unwanted by-products of food breakdown. As an example, most carbohydrate digestion occurs in the small intestine. Digestion occurs with the help of enzymes. Any carbohydrates that weren't digested in the small intestines (ex. fiber) passes into the large intestines. Unlike the small intestines, there are no enzymes to break down the fiber. Instead, bacteria in the large intestine (gut microbiota), ferment the carbohydrates. To better understand the role of enzymes and bacteria, if someone is lactose intolerant, they don't make enough lactase enzxyme to digest lactose effectively. As a result, lactose passes to the large intestine. Water is drawn in by osmosis and is then fermeted by bacteria. This often results in gas, bloating and diarrhea. Anytime undigested carbohydrates pass into the large intestines, bacteria needs to break them down - which results in gas. And if the bacteria in the GI tract are imbalanced, bloating, cramping and gas may be extreme.
When the descending colon is full of stool (feces), it empties contents into the rectum (connects the colon to the anus) and eventually, a bowel movement occurs. The frequency and type of bowel movement can tell a lot about your health. Additionally, because the majority of the immune system is located in your gut, there's a strong relationship between gut health and physical health.
So now that you understand how a bowel movement is formed, it's time to talk about fiber.
Dietary fiber is an important indigestible carbohydrate that slows the transit of foods through the large intestine and promotes regular bowel activity. Residue refers to any type of solid substances that may end up in the large intestines after digestion. High fiber foods, like whole grains, fruits, vegetables, nuts and seeds increase colonic residue. Once the fibrous material enters the colon, water is drawn into the space and binds to the fiber to create stool.
It's important to remember that digestion is a normal process that takes place in resting conditions. Exercise shifts blood flow away from the GI tract and towards the muscles, skin and lungs. As a result, there are significant changes in gut motility, tone and secretion. It's not uncommon for athletes to experience GI distress during exercise. While fiber is extremely important in the daily diet, minimizing foods that could promotes bowel activity, pose a threat to gut bacteria, and increase fecal volume can help reduce the risk of painful and potentially performance-limiting issues on race day such as diarrhea, stomach cramping, gas, reflux, vomiting, nausea or bloating.
A few things to know:
- Even though you are minimizing fiber, you will still have "normal" bowel movements (depending on your regular fiber intake). A low residue diet does not interfere with existing gut contents - those will still be expelled in the mornings during your normal bowel movement.
- A low residue diet may result in a slight decrease in body mass as you won't be accumulating stool for a few days. When combined with carb-loading (which adds weight due to additional muscle glycogn and stored water), athletes may mitigate feeling "heavy" alongside a high-carb diet.
- The period of implementing a low residue diet ranges between 24-72 hours and depends on the athlete, usual fiber intake, normal bowel movements, and past experiences. Following a low residue diet for more than a few days is not encouraged as it may lead to nutrient deficiences and constipation.
- The ultimate goal of following a low residue diet is to reduce the risk of gut discomfort/upset during an event.
- Remember - carb loading is not calorie loading. Here's a helpful blog post on the topic.
- 1 package Organic Ramen Noodles (without seasoning) - 200 calories, 40g carbs, 1g fiber
- 2 Pop Tarts (unfrosted) - 420 calories, 74g carbs, 1g fiber
- 30 Saltine Crackers - 210 calories, 60g carbs, 1g fiber
- 1.5 cup cooked Basmati rice - 480 calories, 108g, 3g fiber
- 2 Belgium Waffles - 320 calories, 46g carbs, 1g fiber
- 9 tbsp cream of wheat - 360 calories, 75g carbs, 3g fiber