The runner’s guide to Carbohydrates

Nutrition
Tuesday, 17 November 2015 1166 Views 0 Comments
The runner’s guide to Carbohydrates

By Deepali Patil

Everything a runner needs to know about this energy source

The primary role of carbohydrates is to provide energy to the body.  It is the body’s preferred source of energy for muscles as well as other biological workings like fat metabolism, providing fuel for the central nervous system, and preventing protein from being used as energy.

The body metabolises carbohydrates into smaller units of sugar namely fructose and galactose. This takes place in the stomach and small intestine from where the smaller units of sugar are absorbed and taken into the bloodstream. On entering the bloodstream they travel to the liver where fructose and galactose are converted into glucose. This glucose is then transported to various tissues and organs, and to the muscles and the brain where it is utilised as energy.

If the body has access to glucose it is stored in the liver and in the skeletal muscles in the form of glycogen. If the glycogen storage is in excess, it is stored in the form of fats in the body, for future use. When the body needs more energy during physical exercises, such as running, it uses these glycogen stores as energy. Glycogen stores are essential for athletic performance, because they serve as an energy reservoir when blood glucose levels are less. This happens due to high intensity exercise or inadequate carbohydrate intake. The body first consumes the blood glucose, and then it uses the glycogen stores in the liver to maintain the energy. The glycogen stored in muscle is used directly by that muscle during exercise; it cannot borrow glycogen from other resting muscles.

Because of limited storage capacity of glycogen only up to 2000 kilocalories or 500 grams, carbohydrate is often known as the ‘Limiting Fuel’ in physical performances. Of this, approximately 400 grams are stored as muscle glycogen, 90-110 grams as liver glycogen, and only 25 grams circulate in the blood as glucose.  How quickly glycogen stores deplete depends on the duration and intensity of the exercise. For instance, in low intensity exercises like distance running, glycogen stores can last as long as 90 minutes but for prolonged high intensity exercises, glycogen stores can provide energy for only 20 minutes.

Foods that contain carbohydrates

According to a study in the Journal of Nutrition and Metabolism, carbohydrates provide 60 per cent of the energy required to make the body work.

There are two types of carbohydrates: simple and complex.

Simple carbohydrates are found in fruits, vegetables, and milk products, as well as in sweeteners like sugar, honey, and syrup.

Complex carbohydrates are found in grains, cereals, wheat, bajra, jowar, maize, ragi, oats, barley, rice, breads, pasta and starchy vegetables such as potatoes, green peas, and corn. Though vegetables such as potatoes, corn, fresh peas and green-beans have carbohydrates in them, the carbs in such foods is present only in small amounts.

Many carbohydrates supply fiber. Fiber is a type of complex carbohydrate. It is found in foods that come from plants like fruits, vegetables, nuts, seeds, beans, and whole grains. Fibrous food prevents intestinal problems, helps lower cholesterol and blood sugar.

Food Items

Carbohydrate Measure

1 cup of cooked rice 45 grams
1 cup of cooked wheat 71 grams
1 cup jowar/ragi/barley 72 grams
Medium-sized potato 30 grams
1 1/2 cup vegetables (green beans, broccoli) 15 grams
0.5 cup (75 g) potato 13 grams
1 cup corn 123 grams
1 cup milk 12 grams
1 banana 30 grams
Jaggery 95 grams

University of Michigan www.med.umich.edu
In the 4th edition of ‘Fundamentals of Foods & Nutrition’ Author Sumati Mudambi and M.V Rajagopal suggests a daily intake of 9-16 servings of 30 grams of carbohydrates each. But this varies depending on the type of physical activity done by the body.

How much carbohydrate is needed by the runner?

The minimum recommended intake of carbohydrates necessary for survival is 130 grams or 520 kcal per day but in athletes the requirement is little more. An average athlete requires 250 grams or 1000 kcal per day as suggested in the study of 2010 featured in the Medicine and Science in Sports and Exercise Journal.

Since carbohydrate recommendations vary with the individual metabolic needs, most athletes consume 6-10 grams of carbohydrate per kilogram of body weight per day (3-5 gm/lb). The recommended carbohydrate intake for athletes is 50-60 per cent of total calories.

Athletes participating in marathons and triathlons have an increased requirement of carbohydrate consumption up to 70 per cent of the daily caloric intake.

To prevent hunger during intense running activity an athlete must consume 250-500 kcal (65-125 grams) of carbohydrates 2-4 hours before the workout. For running over than 90 minutes, consuming carbohydrates 30 minutes into the workout will allow for longer activity. The goal is to consume 15-30 grams of carbohydrates every half-hour depending on the exercise intensity.

What can happen from a lack of carbohydrate?

Adequate amount of carbohydrates are essential for the optimal functioning of the central nervous system. Since the brain uses glucose as its primary energy source, a lack of glucose can result in weakness, dizziness, and low blood glucose levels, a term medically known as hypoglycemia. Reduced blood glucose level during exercise decreases performance and could lead to mental dullness and physical fatigue.

In extreme cases when the body is devoid of glucose it uses proteins as an alternate source of energy. In order to maintain a constant level of blood sugar, the body breaks down proteins to make glucose. Breaking down of proteins puts increased pressure on the kidneys; now have to excrete additional protein byproducts into the urine.

Reference:

http://www.brown.edu

http://www.brown.edu

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