Factors affecting gastric emptying rate

By Glen McGowean

During a race, the last thing we need to be worrying about is weather or not our stomach is going to cooperate. There are many factors that affect our gut during exercise.

The two areas of the gastrointestinal tract (GI tract) we are going to look at are the stomach and the small intestine.

The stomach is a muscular, elastic pouch like organ of the digestive tract that grinds and churns swallowed foods and mixes it with acid and enzymes, forming chime.
No absorption of food actually takes place in the stomach. The absorption of food actually starts in the first section of the small intestine called the duodenum. What we are concerned about during exercise and racing is the emptying rate of the stomach into the small intestine (duodenum ~1 foot, jejunum ~8 feet and the ileum ~11 feet) where the absorption takes place.

Stomach

Below are seven major factors that influence gastric emptying rate.

  1. Stress Psychological and physical stress along with anxiety lead to a decrease in the emptying rate.
  2. Energy (calorie) content An increase in energy content leads to a decreases the emptying rate.
  3. Osmolality Normal osmolality of blood is 280-300mOsm/kg (milliosmoles per kilogram). Foods/liquids with an increased osmolality will lead to a decreased emptying rate. Simply put, osmolality is the measure of concentration of a fluid. Refer to the nutrition panel on the packaging. For example: Gatorade carbohydrate percentage is 6% making this solution hypotonic/isotonic. When a product (drink, gel or bar) has a carbohydrate content percentage at 8% and higher, this may ultimately lead to a hypertonic solution in your stomach slowing or stopping emptying (depending on other factors).
  4. Volume Increase volume leads to an increase emptying rate.
  5. pH Marked deviations from neutral lead to a decreased emptying rate.
  6. Exercise exercise greater that 70-75% VO2 max leads to a decrease in emptying rate
  7. Dehydration Dehydration leads to a decreased emptying rate and a risk of GI distress.

 

Small intestine

Below are five major factors that influence intestinal fluid absorption.

  1. Osmolality Absorption is maximal from solutions containing glucose and sodium closest to that of human blood, also called hypotonic or isotonic solutions. These are found in products or solutions that contain a carbohydrate percentage at 6%-8%.
  2. Carbohydrate An optimal concentration of carbohydrate, especially in the form of glucose in conjunction with sodium will stimulate fluid absorption. Results of recent research suggests that a 6%-8% carbohydrate solution actually enters the bloodstream as rapidly as water but, unlike water, was associated with improved exercise performance.
  3. Sodium Sodium increases the fluid absorption in the proximal small intestine (duodenum). Sodium at 5%-8% in sports drinks aid in the quick absorption of fluid and carbohydrate
  4. Amino acids May enhance fluid absorption.
  5. Anion Anions are atoms or molecules that have gain or lost electrons and therefore have electrical charges. Chloride is the preferred anion to maximize fluid absorption. Chloride is never naturally lacking in the diet. It abounds in food as part of sodium chloride and other salts. Moderate amounts of chloride are found in whole unprocessed foods and processed foods contain large amounts of sodium chloride.

Having noted these factors and keeping in mind that everyone has a different reaction or response to similar foods/liquids or supplementation. Throw in all the factors of racing (stress, heat, exertion and hydration levels) and it can get quite complicated.

Don’t let the biochemical relation that each bullet point explains make this too confusing. Try out different food/liquids and supplementation during training.

Many of you already have your pre-race race and post-race foods all planned out and they work great. Others may not, but this information may give an explanation to your race nutrition.

Never try a new food/liquid/supplement on race day. Always ask your doctor before starting any new program or supplementation.

Eat well, train safe and have fun.