We've all felt a great workout and we've all felt a crummy workout. The difference could be related to carbohydrate intake, or lack thereof. Get yourself a nice cup of tea, water, coffee, wine or your beverage of choice and find a cozy spot. This one's a doozy, as I want to present you with the details.

Main points: 1) It's important to eat/drink carbohydrates if exercising longer than one hour; 2) Varying the types of carbohydrate eaten during exercise increases absorption rate; and 3) To consume enough carbohydrates while exercising, a liquid or solid are both effective.

How Much Carbohydrate (CHO) to Eat DURING exercise?

If exercise lasts 1 hour or less, eating during exercise isn't as crucial. You can grab a bite to eat after your one hour workout.

If exercising longer than 1 hour, eat 30-60 grams of CHO within that hour (120-240 calories).

If exercise continues past 2 hours, increase your CHO intake to 45-90 grams of CHO per hour (180-360 calories) until you're finished exercising. 

This amount of carbohydrate is approximately 20-40 ounces of a typical sport drink. One typical get packet provides around 20-25 grams of CHO. 

One caveat: the amount of CHO an individual athlete consumes during exercise should be determined by trial and error, and strategies for CHO intake should always be developed on an individual basis.

What Type of Carbohydrate to Eat DURING Exercise?

Answer: Eat a Combination of Different Types of Carbohydrates DURING exercise

To maximize carbohydrate absorption during exercise, choose foods and supplements with a variety of different types of carbohydrate. Consuming a mixture of carbohydrate during exercise may speed absorption of carbohydrate in the gut. This is a good thing because it means your body is able to refuel more quickly.

Examples of CHO combination: glucose with fructose, maltodextrin and fructose, glucose with sucrose and fructose.

Carbohydrate from a single sugar source, such as glucose, can only be broken down at rates of approximately 60 grams per hour.

When a combination of carbohydrates are eaten (e.g., glucose and fructose) an amount of about 100 grams per hour can be broken down if large amounts of carbohydrate are ingested (i.e., >140 grams/hour).

Check out the ingredients on the food label to find the type of CHO in the product.

Pros and Cons of Liquid versus Solid CHO DURING Exercise

Pros of drinking CHO in liquid form

  • Replace sweat losses
  • Empty rapidly from stomach

Cons of drinking CHO in liquid form

  • Large volume, difficult to carry
  • Does not provide variety or satiety

Pros of eating CHO in solid form (e.g., gels, chews, banana, etc.)

  • Compact, easy to carry
  • Provide variety and satiety

Cons of eating CHO in solid form (e.g., gels, chews, banana)

  • Require additional water for digestion
  • Does not replace sweat losses

How Quickly Are Different Carbohydrates Digested DURING Exercise?

Rapidly Digested Carbohydrate (approx. 60 grams per hour)

  • Glucose (a sugar formed by the breakdown of starch)
  • Sucrose (table sugar - glucose plus fructose)
  • Maltose (two glucose molecules)
  • Maltodextrins (from starch breakdown)
  • Amylopectin (from starch breakdown)

Slowly Digested Carbohydrate (approx. 30 grams per hour)

  • Fructose (a sugar found in honey and fruits)
  • Galactose (a sugar found in sugar beets)
  • Isomaltulose (a sugar found in honey and sugarcane)
  • Amylose (from starch breakdown)

Sports Drinks: Carbohydrate in Fluids

The focus is on preventing dehydration. As a general guideline, drink 4-8 ounces (roughly 4-8 gulps) of water or sports drink every 15-20 minutes during hard exercise. 

Cool, flavored sports drinks containing 6% to 8% carbohydrate (6g of carbohydrate per 3½ ounces of fluid) in the form of sugars (glucose or sucrose) or starch (maltodextrin) have been shown to effectively provide fuel for immediate energy use and fluid for hydration. Note: ingesting a carbohydrate solution that’s very concentrated is likely to cause gastrointestinal discomfort.

Carbohydrate added to water improves palatability by providing sweetness, provides a source of fuel for active muscles, and stimulates fluid absorption from the intestines. If you need the carbs but don't want to add flavor, there are some flavorless carbohydrate powders you can add to your water. A couple brands I'm familiar with are Nature Smart Carbo-Pro and Unipro Carboplex.

More CHO in a drink is not necessarily better. More than 14g CHO per 8 ounce serving may decrease the rate of gastric emptying and fluid absorption, which can lead to a “sloshy” gut or a stomach or side ache.

Sodium in Fluids

The addition of sodium may help enhance palatability so you drink more, promote fluid retention in your body so you don’t lose as much fluid through sweating, and possibly prevent hyponatremia (low sodium blood levels) in individuals drinking excessively large quantities of plain water. 

Drinking Water and Energy Gels

If you fall behind on your water intake during longer workouts, you run the risk of dehydration, lack of energy, and possible stomach irritation. Studies have shown even moderate dehydration can negatively impact your performance - therefore, it is recommended that an athlete learn to drink during long runs/rides - whether or not they are using an energy gel.

Water is the key to proper gel usage. Gels are absorbed in your small intestine, and water is the transport vehicle that allows this to occur.

Whenever you consume energy gel you should follow it with enough water to properly flush it down (usually a few swallows is sufficient). If you are properly hydrated before your workout you will already have water available in your stomach and intestinal tract that can be used to digest the gel. If you fail to replace this water over time then you will become dehydrated and your performance will suffer as a result.

If using multiple packs of gel during workouts, it is recommended to drink water between gel packs. Drink 4-8 ounces every 15 minutes during endurance events.

Practical Examples

Since all this information can be slightly daunting, I wrote a blog with some practical examples for how to incorporate the carbs during exercise. Check it out at "How to Incorporate Carbs During Exercise."

What products do you use while exercising over a one hour time period?

In Health and Happiness,

Kelly Harrington, MS, RDN

Registered Dietitian Nutritionist for Healthy Goods

 

References:

1. Jeukendrup, A. E. (2004). Carbohydrate intake during exercise and performance. Nutrition 20(7-8):669-677.

2. Jentjens, R. L., and A. E. Jeukendrup (2005). High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose ingested during prolonged cycling exercise. Br. J. Nutr. 93(4):485-492.

3 Jeukendrup, A. E., and R. Jentjens (2000b). Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research. Sports Med. 29(6):407-24.

4. Rosenbloom, Christine, PhD, RD. Sports Nutrition: A Guide for the Professional Working with Active People, 3rd edition. Chicago: American Dietetic Association, 2000.

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