Why Be Concerned with the Glycemic Index?

By Bill Nadeau | Jan. 11, 2010, 12 a.m. (ET)
The offseason is a great time to consider your nutrition plan.  One topic worth revisiting is the glycemic index (GI), as different types of carbohydrate can not only affect race day performance, but also affect your body weight during the offseason.  Are you eating the right types of carbohydrate to keep you satisfied and in a net caloric balance?  Or do you continue to eat sports food samples from race expos for quick meals and snacks?  Our goal is to examine the glycemic index of different foods, the hormonal response by the body to food of different GI, and the effect of eating foods with a specific GI on weight and overall health.

Glycemic index is a tool used to measure the rate at which carbohydrates from different foods are broken down into simple sugars (glucose).  The higher the GI, the greater the rise in blood sugar.  White bread and glucose have a GI of 100%; all other sources of carbohydrate are compared to these reference foods.  If a particular food has a GI of 90, then it produces a rise in blood sugar that is 90% as great as pure sugar.

There are many factors that can influence the GI of a food.  These include the physical form of the food (juice versus whole fruit), the structure of the carbohydrate in the food, the ripeness of the food, and the simultaneous presence of protein, fiber, and/or fat with the food.  For simplicity, here is a short list of the GI of a few commonly eaten foods:
Glucose (table sugar)  100  Orange  48 
Cliff Bar Cookies and Cream  100  Old Fashioned Oatmeal  42 
Rice Krispies  82  Yams  37 
Bagel  72  Skim Milk  32 
Orange Juice  52  Peanuts  14 

The human response to eating carbohydrate-containing foods is quite complex and not solely related to the GI of the food.  Carbohydrate digestion is affected by the resistance of the starch to enzymes in the digestive tract, the activity of enzymes in the intestine, and the presence of other nutrients, such as fat and fiber, that slow stomach emptying.  Further, blood glucose level is not completely regulated by the GI of the food.  Blood glucose can also be affected by the digestibility and absorption of the ingested carbohydrates and the degree of liver uptake (storage as glycogen), as well as insulin secretion and sensitivity of tissue to the action of insulin.

How can eating foods with a lower GI help the triathlete maintain weight in the off-season?  Eating these types of food, such as complex carbohydrates and whole grains will:

  • Avoid drastic drops in blood sugar
  • Slow digestion and provide a longer-lasting supply of energy
  • Subdue hunger-pangs soon after meals and snacks
  • Lessen fatigue
  • Enhance satiety and feelings of fullness

Good choices of low GI foods for meals and snacks include oatmeal, peanut butter, brown rice, quinoa, mixed nuts and low-fat dairy to provide the triathlete with energy as well as a sense of fullness.  Consult with a sports nutritionist who can provide you with personalized recommendations based on your training regimen and weight goals.

Most triathletes are faced with the challenge of weight maintenance during the offseason.  The offseason represents a time of year to store your sports nutrition products in the pantry and reach for wholesome foods with a lower GI.  These foods will fuel you with appropriate energy on a daily basis and help you achieve your health and weight goals.

Bill Nadeau, MS, RD, is a member of the Eat2Win Sports Nutrition team with Trismarter.com. When Bill's not working with athletes on their diets, he can be found training or in the kitchen. Visit www.trismarter.com to learn more about their personalized coaching options such as Tri4Life and Tri2Lose as well as innovative Eat2Win sports nutrition services. Contact: info@trismarter.com or call 917.825.1451 for more information.

strives to provide the highest quality internet-based triathlon coaching and sports nutrition services for the everyday triathlete and novice. These services are based on an understanding of the sport and tailored to the expectations and needs of each and every client. Our services address every aspect of triathlon preparation: Tri4Life personalized coaching, Tri2Lose weight loss and Eat2Win sports nutrition. At Trismarter.com, we celebrate the journey along with our clients from start to finish. 

Foster-Powell K, Holt SHA, Brand-Miller JC: International table of glycemic index and glycemic load values, Am J Clin Nutr 76:5, 2002.

Jenkins DFA et al: Glycemic index of foods: a physiological basis for carbohydrate exchange, Am J Clin Nutr 34:362, 1981.

Ludwig DS, Eckel RH: The glycemic index at 20 y, Am J Clin Nutr 76:264S, 2002.