Excellent Article on Nutrition for Endurance Diabetic Athletes

Nutrition Needs for Diabetic Endurance Athletes

By Kimberly J. Mueller, MS, RD, CSSD

Have you recently been diagnosed with diabetes? Are you confused with how many carbohydrates you need to prevent erratic blood sugars and to enhance endurance performance? This article explores the latest research findings on nutrition for diabetic runners. Read on….

Introduction

It is estimated that some 16 million Americans currently suffer from diabetes mellitus with one-third of this population being undiagnosed cases. By 2025, trends indicate that an additional 6 million Americans and a total population of over 300 million worldwide will have diabetes. While the vast majority of individuals diagnosed have Type 2 Diabetes (formerly known as non-insulin dependent diabetes), more than 1 million individuals have Type 1 diabetes (formerly known as insulin dependent diabetes). Because Type 2 diabetes is generally associated with insulin resistance secondary to excessive body fat, this type of diabetes is far less common among an athletic population that includes runners. In contrast to Type 2 diabetes, Type 1 diabetes is typically triggered by an environmentally triggered autoimmune process that destroys pancreatic beta-cells, thereby rendering the body unable to manufacture insulin. Because of the inability to produce insulin, it is essential that Type 1 diabetics take insulin to help regulate their blood sugars. Furthermore, diet plays a critical role in prevention of both hyperglycemic (excessive blood sugar), which can lead to blindness, nerve damage, and kidney failure, and hypoglycemia (low blood sugar), which can lead to loss of concentration, shaking, shivering, and loss of consciousness. This article will explain the most important nutrition implications and recommendations for diabetic endurance athletes.

Role of Insulin in the Body

Secreted by the pancreas in response to consumption of carbohydrate-rich foods, insulin influences the metabolism of all body fuels and is essential for muscle development, growth, and energy. Perhaps the most recognized role of insulin and the most relevant for diabetic athletes is its ability to promote uptake and storage of glucose in muscle and fat cells. In the muscle, glucose is stored as glycogen, whose upkeep is important for prevention of the dreaded “wall” during endurance exercise and also helps enhance recovery by replenishing the glycogen used during exercise. In fat cells, the glucose is used to make fat, which can be released into the bloodstream as fatty acids and used as an alternative and more efficient fuel source during endurance exercise.
Insulin activity is diminished in both Type 1 and Type 2 diabetics. In Type 2 diabetics, there is increased insulin resistance secondary to a defect in an insulin receptor site or insulin-directed metabolism, leading to decreased insulin function throughout the entire body. In contrast, Type 1 diabetics fail to produce sufficient amounts of insulin, leading to elevated blood sugars (hyperglycemia), which is marked by increased thirst, hunger, and urination. If insulin resistance and blood sugar control are not improved through diet and exercise, blood insulin levels will increase leading to hyperinsulinemia, which is associated with increased risk for heart disease and heart attacks secondary to decreases in HDL cholesterol (aka “good cholesterol”), sodium retention, periodic high blood pressure, and high triglycerides.
Insulin activity and/or regulation of blood sugars in both Type 1 and Type 2 diabetics can be optimized through proper diet and exercise. One study discovered a 90% improvement in insulin activity upon completion of a 15-day fitness routine that included daily walking at 60% of the maximal aerobic capacity for 35 minutes.1 In addition, diabetics engaged in regular endurance activity such as running and cycling over a period of a year can increase glucose uptake by as much as 30%.2 Diet, which is discussed in the next section, also plays a significant role in the maintenance of optimal blood sugars.

Controlling Blood Sugars and Insulin Activity with Diet

The diabetic diet is a well-balanced meal plan that includes intake of all the foods specified in the Food Guide Pyramid (see Figure 1). The foods specified in the pyramid contain the following 3 energy-containing nutrients whose balance is paramount for regulation of blood sugars and peak performance:
• Carbohydrates: Foods rich in carbohydrates include bread, rice, pasta, cereal, crackers, chips, starchy vegetables (potatoes, corn, peas), fruit, milk and milk products, beans, cookies, and sugar.
• Fats: Foods rich in fat include avocados, coconut, olives, nuts, seeds, fried foods, high-fat meats such as ribs, bacon, and sausage, high-fat dairy foods such as ice cream, whole milk, and cheese, butter and margarine, oils.
• Protein: Foods rich in protein include legumes, nuts, dairy products such as milk, cottage cheese, and yogurt, meat, fish, poultry, soy products.
The main controversy with respect to creating a diabetic meal plan is how to balance out each of these nutrients. Some scientists believe that a diet rich in protein and fat with dietary restriction of carbohydrates will optimize blood sugar control and insulin activity while other scientists believe that a moderate intake of carbohydrate and protein with dietary restriction of fat will best serve the diabetic individual. However, before determining a balance that is conducive to optimal blood sugar control and peak performance, it is essential to calculate energy needs based on individual training demands.

Figure 1. American Diabetes Association Food Guide Pyramid



Calories

Energy in food is measured in calories. As an endurance athlete, energy demands are significantly higher than less active individuals due to the increased daily expenditure from physical activity. The goal for maintenance of lean mass is to obtain energy balance, which means energy consumption equals energy expenditure. More often than not, endurance athletes have trouble keeping up with their high calorie demands, which can lead to a negative energy balance. If severe enough, catabolism of lean mass occurs, thereby increasing risk for muscular injury. Furthermore, symptoms of hypoglycemia become more prevalent. Those wishing to drop body fat should not restrict more than 1,000 calories per day. Those athletes with a goal of increasing lean mass should consume slightly more calories (+250-500 calories) than they expend while maintaining their fitness routine. Diabetic endurance athletes have the same energy needs as non-diabetic athletes. Table 1 will help with calculation of individual energy needs based on daily activity.

Table 1. Daily energy needs based on activity level

ACTIVITY LEVEL DESCRIPTION OF ACTIVITY DAILY CALORIE REQUIREMENT PER POUND OF BODY WEIGHT
Less active Little or no sport activity 14-15
Moderate 45-60 minutes of moderate-intensity sport activity 16-20
Very Active 60-120 minutes of moderate-intensity sport activity 21-25
Extremely Active 120+ minutes of moderate-to-intense sport activity 25-30+
*Information adapated from Endurance Sports Nutrition by Suzanne Girard Eberle, MS, RD

Carbohydrates

The only food nutrient that can directly influence blood sugars and consequent energy levels are carbohydrates. During metabolism, carbohydrates are broken down into sugar, entering the bloodstream as glucose. In response to the rise in blood sugars, the pancreas releases insulin, which helps transport sugar from the blood into the muscles for energy production. Because of the nutrient’s primary role of supplying glucose or energy to our working muscles and brain, a diet rich in carbohydrates can help improve endurance performance. However, there is controversy as to whether a carbohydrate-rich diet is healthy for individuals with diabetes since insulin activity is compromised. Some scientists believe that a diet higher in protein and fat will help keep insulin levels at bay, helping the diabetic athlete control their blood sugars and perform at peak levels. More relevant, however, is the glycemic response of the carbohydrate. Instead of replacing all carbohydrates with protein-rich foods, which also tend to be higher in fat content, most health professional are encouraging diabetic athletes to limit their intake of refined carbohydrates (e.g., refined sugar and flour), which tend to spike insulin and cause hypoglycemia, and include more complex carbohydrates that contain some fiber (e.g., whole grains, most fruits) or protein (beans, low-fat dairy, sprouted wheat, soy).
The rate at which carbohydrates raise blood sugar and consequent insulin is measured by glycemic index (see www.mendosa.com/gilists.htm for listing of glycemic values of foods). Carbohydrate-rich foods with a high glycemic value enter the bloodstream rapidly, leading to a quick rise in blood glucose and the release of insulin. Several athletes complain of the hypoglycemic response associated with consumption of high glycemic foods. Furthermore, ingestion of high glycemic carbohydrates stimulates an enzyme called Lipoprotein Lipase (LPL), which has been named the “gatekeeper for fat storage by fat cells”. This enzyme sends the message to store foods in the fat cells, which is one suggested reason why the American population is getting fatter and experiencing more chronic disease.3 In a survey conducted at Harvard University’s School of Public Health, it was determined that of the top 20 carbohydrates ingested by Americans, 16 were high glycemic (see table 2). In fact, high glycemic snack foods comprise 25% of total caloric intake in the U.S.
In contrast, low glycemic foods, which tend to be higher in fiber or contain some protein, are converted into glucose slower than high glycemic foods and therefore, less insulin is needed to regulate blood sugar. In fact, fasting insulin levels have been shown to decline by 10% when consuming low-glycemic whole grains rather than high glycemic refined white flour.4 In addition, researchers believe that decreasing the intake of insulin-stimulating high glycemic foods will increase insulin activity by at least 50%, helping to improve glucose utilization during exercise and prevent cardiovascular disease. Finally, the hypoglycemic response associated with high glycemic foods is muted when replaced with low glycemic foods (see table 2 for low glycemic replacements). Therefore, diabetic athletes are encouraged to consume approximately 50-60% of their total daily calories from low-glycemic carbohydrates or approximately 3 grams per pound of body weight.

Table 2. Top 20 Carbohydrates Ingested By Americans

TOP 20 CARBOHYDRATES
INGESTED BY AMERICANS GLYCEMIC STATUS CHOOSE THIS LOW-GLYCEMIC FOOD INSTEAD…
1. Potatoes, white
2. White bread
3. Cold breakfast cereal
4. Dark bread
5. Orange juice
6. Banana
7. White rice
8. Pizza
9. Pasta
10. Muffins
11. Fruit punch
12. Coca-Cola (regular)
13. Apple
14. Skim milk
15. Pancake
16. Table sugar (sucrose)
17. Jam (with sugar)
18. Cranberry juice (with sugar)
19. French fries
20. Candy 1. High
2. High
3. High
4. High
5. Acceptable
6. High
7. High
8. Very high
9. Acceptable
10. High
11. High
12. High
13. Acceptable
14. Acceptable
15. High
16. High
17. High
18. High
19. High
20. High 1. Sweet potato
2. Sprouted wheat bread
3. Old Fashioned Oatmeal
4. 100% whole grain rye
5. Unsweetened apple juice
6. Peach
7. Parboiled High Amylose Rice
8. Cheese tortellini
9. Cheese Ravioli
10. 100% whole wheat bagel
11. Unsweetened peach juice
12. Diet Coke
13. Strawberries
14. Low-fat yogurt or cottage cheese
15. Buckwheat pancake
16. Fructose
17. Simply Fruit jam
18. Unsweetened pear juice
19. Mixed green salad
20. Fig Newton

Protein

Protein has several critical functions in the body, including creation of new cells when old ones die, formation of antibodies (which fight viruses and bacteria), creation of a visual pigment to help eyesight, formation of enzymes (e.g., digestive enzymes), and formation of hormones such as insulin. Furthermore, recent research suggests that protein in combination with carbohydrate (mixed meal) increases insulin activity by almost 50%. During metabolism, protein is broken down into amino acids which collect in a pool in our liver. These amino acids are relied upon to build protein for completion of the roles listed above. If protein intake is inadequate, the amino acid pool becomes dehydrated and catabolism of muscle tissue occurs. Excessive protein that the body does not need causes an overflow of the pool, which, despite myth, does not increase muscle mass. Rather, the kidneys work overtime to filter out the toxic byproducts of protein metabolism and the overflow of protein is stored as fat.
While it is well established that endurance athletes require more protein, there is no evidence suggesting an elevated protein intake will help with better blood glucose control in diabetic athletes. Therefore, diabetic athletes can follow the same recommendations as their non-diabetic counterparts, consuming approximately 15-20% of their total calorie intake from protein or approximately 0.55 to 0.75 grams per pound of body weight. Because of the increased risk for cardiovascular disease in diabetics, such lean protein sources as chicken or turkey (without skin), baked or broiled fish, soy products, round steaks, ‘loin’ cuts, and egg whites are recommended.

Fat

While fat provides a concentrated source of energy (almost double the potential energy of carbohydrates and protein), helping to spare glycogen reserves during prolonged exercise, excessive dietary intake of fat can have a profound impact on disease processes and can diminish endurance performance. Previous research confirmed the detrimental effects of saturated fats, which are found in animal foods and tropical oils, with respect to risk for cardiovascular disease in diabetics. More recently, however, researchers have discovered that saturated fat is not the worst type of fat. Instead, trans fatty acids, indicated by the word “hydrogenated” on food labels, play a larger role in the development of chronic disease.5,6 Trans fatty acids are found in vegetable shortenings, some margarines, crackers, cookies, cakes (especially pound cake), and many other foods made with or fried in partially hydrogenated fats. Risk for chronic disease can be substantially reduced if trans fatty acids and saturated fats are substituted with unsaturated fats—either polyunsaturated fats (mayonnaise, vegetable oils) or monounsaturated fats (fish oils, canola oil, olives, nuts). Overall, fat should not exceed 30% of the total calories consumed with no more than 10% coming from saturated and hydrogenated fats.

Dietary Recommendations for Endurance Sport Activity

The principle risk of endurance sport activity among diabetics, especially Type 1 diabetics, is hypoglycemia. Sustained aerobic activities, such as running, cycling, and swimming, rely on a mix of aerobically processed fuels, but the major sources are fats and carbohydrates. As the intensity of the activity rises, as in interval training or tempo runs, glucose utilization continues to increases, causing an array of hormonal responses including a decline in endogenous insulin and a corresponding increase in exogenous insulin absorption, all of which increase the risk for hypoglycemia.7 Therefore, diabetic athletes participating in prolonged exercise such as marathons, triathlons and long practices are recommended to supplement with carbohydrate and adjust their insulin dose accordingly as means to compensate for the accelerated glucose uptake during the activity.8

Pre-Exercise

A light-to-moderate pre-exercise meal helps to restock liver glycogen stores, which can be depleted if in a fasted state (haven’t eaten for 4 or more hours). Liver glycogen is converted back to glucose to maintain normal blood sugar during the initial stages of exercise. In exercise bouts lasting less than hour, additional carbohydrates are generally not needed unless blood sugars are less than 100 mg/dL. If blood sugars are low, it is desirable to consume a small snack consisting of approximately 15-30 grams of low glycemic carbohydrates (see table 3) to help prevent a hypoglycemic event.
In preparation for aerobic exercise lasting greater than 1-hour, a more substantial meal is recommended unless blood sugars are over 200 mg/dL. For every hour prior to the start of exercise, the diabetic athlete should consume a well-balanced meal that includes approximately 30-50 grams of low-glycemic carbohydrates. Make sure to allow adequate time for digestion. In addition, it is recommended to consume approximately 16 ounces of fluids—water or a sports drink with <10% carbohydrate—within the hour leading up to exercise start.

Table 3. Carbohydrate Intake Recommendations for Sport Activity

Type of Activity Blood Glucose Level Carbohydrate Intake Recommendations Example of Snack
Short duration at low-to-moderate intensity exercise (e.g., walk ½ mile, leisure bike <30 minutes) <80 mg/dL

>80 mg/dL 30 grams

10-15 grams 1 cup canned fruit (in juice)

1 orange
Moderate intensity exercise
(swim, jog, cycling for 1 hour) <80 mg/dL


80-180 mg/dL

180-300 mg/dL

300+ mg/dL 30 grams + small amount of protein

10-15 grams

No extra food

Exercise not recommended ½ peanut butter sandwich


1-2 Figs

High intensity strenuous exercise (running race, interval workout, strenuous cycling or swimming, exercise longer than 1-hour) <80 mg/dL





80-180 mg/dL


180-300 mg /dL


300+ mg/dL ~50 grams plus some protein




30 grams plus some protein

10-15 grams plus some protein

Exercise not recommended Blend 1 cup apple juice with 1 cup light or plain yogurt, 1 Tbsp protein powder and 1/2 cup raspberries.

12 ounces Accelerade (drink immediately prior)

1/3 Powerbar (eat immediately prior)


During Exercise

In training bouts lasting longer than 60 minutes, there is profound evidence that supplementation with carbohydrates will help enhance endurance performance by aiding fat metabolism and preserving both glycogen and protein. For diabetic athletes, supplementation with carbohydrates also helps prevent a drop in blood sugar and consequent hypoglycemic symptoms which can be dangerous. Recent research by Edmund Burke at the University of Colorado at Colorado Springs suggests that a small amount of protein consumed with carbohydrate in a 1:4 ratio during exercise may double insulin activity and glucose uptake.9 Recommendations for diabetic endurance athletes, therefore, include consuming approximately 15-30 grams of carbohydrate and 4-8 grams of protein for every 15-30 minutes of exercise. This would be equivalent to 1-2 energy gels combined with 1-2 Tbsp of protein powder or consumption of one Powerbar each hour of exercise. Note that high glycemic carbohydrates are appropriate during exercise due to their ability to respond quickly to hypoglycemia.

Post-Exercise

In addition to the beneficial effects of consuming a 4:1 ratio of carbohydrates to protein during exercise, Dr. John Ivy at the University of Texas at Austin has discovered that the same ratio consumed within 30 minutes post-exercise can reduce post-workout muscle damage by 36% by increasing glucose uptake by the muscles for repletion.10 Diabetic athletes may further benefit from this snack by preventing postexercise, late-onset hypoglycemia, which can occur up to 24 hours following exercise.11 While specific post-exercise recommendations have not been made for diabetic athletes, it is recommended that endurance athletes consume about 1/2 gram of carbohydrate and 1/8 gram of protein per pound of body weight within 30 minutes after finishing an event. Diabetics may have to adjust their insulin accordingly depending on where their blood glucose is. Because glycogen repletion occurs at a rate of only 5-7% per hour, diabetics should continue to consume small, frequent meals every 2-3 hours that are rich in low-glycemic carbohydrates and include small amounts of protein.

Additional Dietary Recommendations for Diabetic Athletes

1. Eat at least six small meals in 2-4 hour increments throughout the day to prevent peaks and lows.
2. If drinking alcohol, do so in moderation: no more than 1 drink per day for women and 2 per day for men.
3. Always carry sugar in some form with you (glucose tablets and hard candies are popular because they aren’t messy).
4. Exercise with someone else who knows you have diabetes or wear an ID tag.
5. Make sure to self monitor blood glucose to help determine your food and insulin needs.
6. Drink plenty of fluids throughout the day to prevent dehydration: Aim at ½ your body weight in fluid ounces of non-carbonated and non-caffeinated beverages.
7. Aim at 25-30 grams of fiber per day to help stabilize blood sugars. Good sources include whole grains, colorful fruits and vegetables, and beans.
8. A multi-vitamin/mineral supplement serves as a nutrition insurance agent. Diabetics may also benefit from additional chromium, folic acid, B-6, and B-12.
Summary

Despite an onslaught of mixed messages for diabetics and the American consumer, the best diet for blood sugar control and optimal insulin activity is one that includes all the foods in the food guide pyramid in a balance of approximately 50-60% low-glycemic carbohydrates, 15-20% protein, and <30% fat. In addition, restriction of hydrogenated fats (no more than 10% of total calorie intake) has important implications for reducing risk for chronic disease. To prepare accordingly for endurance exercise, self monitoring of blood sugars is critical to determine the correct dose of carbohydrates for prevention of hypoglycemia during exercise. Consuming a small amount of protein with carbohydrate—in a 1:4 ratio--during exercise may help increase glucose utilization, thereby sparing glycogen and enhancing endurance performance. This same ratio of protein to carbohydrates seems to be beneficial for post-workout recovery and prevention of late onset postexercise hypoglycemia in the diabetic athlete.

Kimberly J. Mueller, owner of Fuel Factor (www.Fuel-Factor.com), is a Registered Dietitian with a master’s degree in Exercise Physiology as well as a competitive endurance athlete competing in triathlon, cycling, and running events. She provides nutritional counseling and custom meal planning to athletes around the world. Kim can be contacted at kim@Fuel-Factor.com.








































Works Cited

1. Zivanic S, Cizmic M, Dragojevic R, Vanovic M. Is there a direct connection between (VO2) max increase and insulin resistance decrease after aerobic training? Program and abstracts of the 35th Annual Meeting of the European Association for the Study of Diabetes; Sept 28-Oct 2, 1999; Brussels, Belgium. Abstract 186.

2. Borghouts LB, van Kranenburg GPJ, Schaart G, Keizer HA. Long-term endurance training induced changes in insulin sensitivity, muscle enzymes and Glut4 in NIDDM patients. Program and abstracts of the 35th Annual Meeting of the European Association for the Study of Diabetes; Sept 28-Oct 2, 1999; Brussels, Belgium. Abstract 187.

3. Liu S, Willett WC, Stampfer MJ, Hu FB, Franz M, Sampson L, Hennekens CH, Manson JE. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nutr. 2000; 71(6): 1455-1461.

4. Pereira MA, Jacobs DR, Pins JJ, Raatz SK, Gross MD, Slavin JL, Seaquist ER. Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults. Am J Clin Nutr. 2002; 75(5): 848-855.

5. Salmeron J, et al. Dietary fat intake and risk of type 2 diabetes in women. Am J Clin Nutr. 2001; 73(6): 1019-1026.

6. Ascherio MD, Katan MB, Zock PL, Stampfer MJ, Willett WC. Trans fatty acids and coronary heart disease. N Engl J Med. 1999; 340(25): 1994-1998.

7. Koivisto VA, Felig P. Effects of leg exercise on insulin absorption in diabetic patients. N Engl J Med. 1978; 298(2): 79-83.

8. Sane T, Helve E, Pelkonen R, et al. The adjustment of diet and insulin dose during long-term endurance exercise in type 1 (insulin-dependent) diabetic man. Diabetologia. 1988; 31(1): 37-41.

9. Ready SL, Seifert J, Burke E. Effects of two sport drinks on muscle stress and performance. Abstract presented at National Meeting of the American College of Sports Medicine, 1999.

10. Williams M, Ivy J, Raven P. Effects of recovery drinks after prolonged glycogen-depletion exercise. Abstracts presented at Mid-Atlantic Regional Meeting, 1998, and National Meeting of the American College of Sports Medicine, 1999.
11. Hernandez JM, Maccia T, Fluckey JD, Ulbrecht JS, Farrell PA. Fluid snacks to help persons with type 1 diabetes avoid late onset postexercise hypoglycemia. Med Sci Sport Exerc. 2000; 32(5): 904-991.

Recommended Readings

Chalmers KH, Peterson AE. 16 Myths of a Diabetic Diet. American Diabetes Association: Alexandria, VA, 1999.

de Wees Allen, A. Complete Guide to Fat-Storing Carbohydrates, Edition VII. Glycemic Research Institute: Washington D.C, 2000.

Girard-Eberle, S. Endurance Sports Nutrition. Human Kinetics: Champaign, IL, 2000.

Glycemic Research Institute. Low Glycemic Food Plans and Recipes. Glycemic Research Institute: Washington D.C., 2000.

Shilstone, M. Lose Your Love Handles. Berkley Publishin