November 2009 Issue

Guidelines for the Casual Exerciser
By Janice H. Dada, MPH, RD, CSSD, CHES
Today’s Dietitian
Vol. 11 No. 11 P. 18

I once overheard a newly diagnosed, normal-weight diabetes patient ask a nurse educator what he should eat before a run. I was baffled when the nurse responded by saying, “Why don’t you just walk instead of run?” Why would she discourage this patient from continuing his exercise routine? It is true that exercising with diabetes must be planned carefully, but exercise is such an important aspect of diabetes care that the benefits far outweigh the potential risks. This nurse clearly lacked the knowledge to explain basic exercise nutrition guidelines to this runner and should have referred him to an RD with sports nutrition expertise.

This article will outline some basic guidelines to assist RDs in explaining basic nutrition principles to the casual exerciser with diabetes.

The Role of Exercise in Diabetes Management
Physical activity is a vital component of the diabetes treatment plan. There are many health benefits of being physically active for people with diabetes, including a reduced cardiovascular disease risk, promotion of a healthy body weight, reduced body fat, and an improved sense of well-being. In addition, exercise significantly improves blood glucose control by increasing peripheral insulin sensitivity, reducing insulin needs, and improving glucose tolerance.1,2

The casual exerciser with diabetes may need assistance with his or her diabetes management to maintain euglycemia. This includes adjusting medications, types and amounts of food consumed, meal timing, and, in some cases, the actual exercise regimen. Glucose fluctuations and management challenges can be especially predominant in individuals with type 1 diabetes because they completely lack the ability to make metabolic adjustments to manage fuel homeostasis. RDs can play an essential role in helping individuals with type 1 and type 2 diabetes maintain glycemic control while being physically active.

Exercising With Diabetic Complications
People with diabetes who are in good metabolic control and do not have serious diabetic complications may participate freely in competitive or recreational activities. However, certain diabetes comorbidities warrant further attention. Conditions such as neuropathy, retinopathy, nephropathy, and cardiovascular disease are common complications associated with diabetes that has been poorly controlled over time. Individuals with these conditions will need further evaluation to determine the most appropriate physical activities in which to participate. For instance, in advanced peripheral neuropathy, non–weight-bearing exercises such as swimming or stationary biking are recommended.2

Fuel for Exercise
Clients often report to me that they avoid food before and/or after exercise so as not to negate the benefits of the exercise performed. Some clients have also confessed the liberal diets they allow themselves after exercise, despite how minimal their exertion may have been. However, research has shown that eating prior to exercise increases one’s energy levels and results in an increased number of calories burned. Postexercise nutrition is equally important for replenishing glycogen stores and repairing the micro-tears that muscle may sustain during activity. An individual should consume a meal or snack within two hours prior to exercise and within 30 minutes after exercise. Specific nutrient guidelines should be individualized based on the type, amount, and intensity of exercise performed.

The following guidelines summarize nutrient needs for varying levels of activity3:

Calories (kcal per pound of body weight):
• Sedentary: 13 to 15 kcal/lb
• Low Active (30 to 60 min/day): 16 to 18 kcal/lb
• Active (1 to 1.5 hours/day): 19 to 21 kcal/lb

Carbohydrates (grams carbohydrate per kilogram body weight):
• Low Active activity level with desired weight loss: 2 to 5 g/kg
• Active for 1 hour/day: 5 to 7 g/kg

Protein (grams per kilogram body weight):
• Sedentary: 0.8 g/kg
• For endurance exercise: 1.2 to 1.4 g/kg
• For strength training: 1.6 to 1.7 g/kg

Fat: 20% to 35% of total kilocalories

Fueling During Activity
Individuals engaging in endurance exercise lasting longer than 45 to 60 minutes need supplemental fluids and calories. Carbohydrate supplements are useful during longer duration exercise or when energy expenditure is high. When blood glucose is under 100 mg/dL before exercise, the individual should consume additional carbohydrate. Muscle efficiency and performance are optimized when blood glucose remains between 70 and 150 mg/dL during exercise.1

Approximately 15 to 30 g carbohydrate should be consumed every 30 to 60 minutes to maintain euglycemia and promote exercise performance. Sports drinks with 4% to 8% carbohydrate provide a convenient vehicle for both maintaining hydration and consuming carbohydrate. Sports bars and gels offer another convenient option for carbohydrate consumption during activity, but these should be consumed with plenty of fluid. Supplementing carbohydrate during activity should be carefully tailored to the activity and the individual. Blood glucose should be monitored about every one to two hours after exercise, if possible, to evaluate response to activity and to fine-tune the individual’s supplementation protocol.

Exercise Precautions

Elevated Preexercise Blood Glucose
In general, if fasting blood glucose is over 250 mg/dL before exercise, urine ketones should be tested. The presence of ketones indicates poor metabolic control, the need for more insulin, and that exercise should be delayed. Blood glucose over 300 mg/dL, regardless of the presence of ketones, always means that exercise should be delayed. Supplemental non-caloric fluids are necessary to prevent dehydration and clear ketones.

Hypoglycemia
Those who control diabetes via diet and exercise alone are not at increased risk of hypoglycemia during activity. Individuals using insulin secretagogues or exogenous insulin to treat diabetes are at an increased risk of experiencing hypoglycemia. To prevent hypoglycemic events during physical activity, it is necessary to monitor blood glucose and adjust medications and food intake accordingly. It is important that glucose gels or tabs are always carried during activity to treat hypoglycemia should it occur.1,2

Dehydration
People with diabetes are at increased risk of becoming dehydrated. When blood glucose is high, excess water is lost in the urine. Additionally, thirst centers in the brain are not activated until a 1% body water loss has occurred.2 Because of this, it is important that exercise be initiated in a hydrated state and that a fluid consumption schedule during exercise be established. Some basic fluid guidelines follow3:

Before exercise:
• Consume 16 to 20 oz two hours prior to exercise.

During exercise:
• Consume roughly 8 oz every 15 minutes.
• Sodium and carbohydrate replacement are necessary for exercise lasting more than one hour.

After exercise:
• Drink 24 oz for every pound of body weight lost during activity. The individual should weigh before and after activity to ensure proper rehydration occurs.

Insulin and Dietary Adjustments for Fitness Activities
Pattern management is key to maintaining optimal blood glucose control with physical activity. RDs can be of great benefit by assisting clients with pattern management, which involves the following six steps4,5:

• Step 1: Record glucose readings.
• Step 2: Study the recorded information.
• Step 3: Find and interpret patterns.
• Step 4: Make adjustments based on patterns.
• Step 5: Implement adjustments.
• Step 6: Evaluate glucose response.

In general, a 30% to 50% reduction in preexercise insulin (or any insulin whose action profile continues through the time period of the activity) is necessary.1 Doses may also need to be adjusted after physical activity, as the increased insulin sensitivity caused by exercise can last up to 36 hours after unusual or intense exercise. Intensive insulin therapy (multiple daily injections and continuous subcutaneous insulin infusion) is considered the gold standard for treating type 1 diabetes and is more likely to allow safe and optimal exercise performance as well.1

— Janice H. Dada, MPH, RD, CSSD, CHES, is a dietitian, college nutrition instructor, and freelance writer based in southern California. Her areas of expertise include diabetes, weight management, wellness, and sports nutrition.

 

References
1. Dunford M, ed. Sports Nutrition: A Practice Manual for Professionals. 4th ed. American Dietetic Association; 2006: 355-366.

2. Colberg S. The Diabetic Athlete: Prescriptions for Exercise and Sports. Champaign, Ill.: Human Kinetics; 2001.

3. Kundrat S, Rockwell M. Sports Dietetics: Practiced, Proven, and Tested Manual. Nutrition on the Move, Inc; 2008.

4. Hinnen DA, Guthrie DW, Childs BP, Guthrie RA. Pattern management of blood glucose. In: Franz MJ, ed. A Core Curriculum for Diabetes Education. 4th ed. Chicago: American Association of Diabetes Educators; 2001:173-197.

5. Exercise. In: Walsh J, Roberts R. Pumping Insulin. 2nd ed. San Diego, Calif.: Torrey Pines Press; 1995:83-95.