Optimal nutrition during prolonged exercise

Prolonged exercise is considered more than 60 minutes of activity. If you exercise for more than 60 minutes or participate in an endurance race lasting more than 60 minutes, you will benefit from drinking a carbohydrate/electrolyte solution during the exercise.

It is generally accepted that 600 to 1200 ml per hour of fluid should be consumed, containing between 30 and 60 grams of carbohydrates and 0.5 to 0.7 grams of sodium (Na) per liter of fluid (Von Duvillard SP, et al. 2004). One liter is 1000 ml.

The carbohydrates help to prevent glycogen depletion and will help to improve performance. Carbohydrates are stored in the form of glycogen in the muscles and the liver and used as needed for energy. When glycogen stores are completely used up and energy has to be supplied mainly by fat, performance will be substantially reduced. The body will also start to break down its own protein at that point to help supply energy.

Sodium is important to help maintain fluid balance and prevent muscle cramping.

What is the best form of carbohydrates to use for this purpose and how much can we utilize?

The carbohydrates without doubt are important because they help improve performance, but it’s a limit to what we can absorb because the rate of gastric emptying. What has been commonly used is a solution of 4% to 8% carbohydrates per 100 ml of fluid.

Comparatively new research shows that a combination of glucose and fructose allows for more carbohydrates to be absorbed than if only a single source like glucose is used by itself.

It has been documented that during 120 minutes of cycling exercise when glucose of 1.2 grams per minute and 0.6 grams per minute of fructose was combined, it improved performance by 8%, compared to when glucose only was used (Currell K, Jeukendrup AE. 2008). This amount of carbohydrate would be 108 grams per hour, which is considerably more than the 60 grams commonly used.

Glucose is a high glycemic index carbohydrate and another source of high glycemic carbohydrate which has been used in many studies is maltodextrin.

Summary: When competing in an endurance race or exercise for more than 60 minutes, drink a carbohydrate solution consisting of glucose or maltodextrin and fructose. The drink should also include 0.7 grams of sodium per liter of fluid. The ratio of glucose to fructose should be 2:1 and the amount of total carbohydrates should not be exceeding 108 grams per hour, not exceeding 1200 ml of fluid per hour.

Start to drink early, probably before the first 60 minutes of activity, and drink every 15 minutes.

Don’t drink this type of high glycemic index solution when you are not exercising because that would, with time, make you less insulin sensitive.

You want to be as insulin sensitive as possible to allow maximum amount of glucose to be transferred into the cells for energy.

Currell K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008 Feb;40(2):275-81.

Von Duvillard SP, Braun WA, Markofski M, Beneke R, Leithäuser R. Fluids and hydration in prolonged endurance performance. Nutrition. 2004 Jul-Aug;20(7-8):651-6.