Stella Lucia Volpe, Ph.D., R.D., L.D.N., FACSM, is an associate professor and the Miriam Stirl Term Endowed Chair in Nutrition in the Division of Biobehavioral and Health Sciences at the University of Pennsylvania, Philadelphia, PA. She is a member of the Gatorade Sports Nutrition Board. Her degrees are both in Nutrition and Exercise Physiology, and she also is ACSM Exercise Specialist® certified. Dr. Volpe's research focuses on obesity and diabetes prevention, using traditional interventions, mineral supplementation, and more recently, by altering the environment to result in greater physical activity and healthy eating. Dr. Volpe is an associate editor of ACSM's Health & Fitness Journal®.
Exercising with any type of chronic disease can be challenging. Type 1 diabetes mellitus (DM) is a disease that impacts a person's diet in relation to his/her exercise regime. In this Nutritionist's View, the focus will be on eating and exercising for individuals with type 1 DM.
OVERVIEW OF TYPE 1 DM
"Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both" (1). In type 1 DM (formerly known as "juvenile-onset diabetes" and "insulin-dependent diabetes mellitus [IDDM]"), the beta cells of the pancreas do not manufacture insulin, or make it in such small concentrations that the body is unable to use glucose (blood glucose) for energy, resulting in hyperglycemia (Figure). As a result, the body starts to break down fat stores for energy. Despite the fact that fat has greater energy than carbohydrates, the greater fat metabolism leads to a buildup of compounds called ketone bodies. Ketone bodies can be used by the brain and central nervous system as an energy source for a short time; however, the buildup of ketone bodies makes the blood more acidic and can result in something called metabolic ketoacidosis, leading to coma and possibly death. The brain and central nervous system preferentially use glucose for energy.
Figure. Figure from ...Image Tools
Type 1 DM could be a result of an autoimmune response where the body attacks its own pancreas and/or caused by a virus that attacks the pancreas (1). Type 1 DM characteristically occurs in individuals aged 20 years and younger; however, in most cases, its onset is around the age of 10 to 12 years in girls and 12 to 14 years in boys. In the United States, type 1 DM accounts for approximately 5% to 10% of all cases of DM (1).
Individuals who have uncontrolled type 1 DM are usually: underweight or of normal body weight, have frequent urination (polyuria), are frequently hungry (polyphagia), are frequently thirsty (polydipsia), have hyperglycemia (high levels of blood glucose), and have ketotic breath (sweet-smelling breath) (2).
NUTRITION RECOMMENDATIONS FOR PEOPLE WITH TYPE 1 DM
In general, people with type 1 DM are encouraged to consume meals and snacks at usual times each day. This will help to maintain blood glucose levels within normal limits and also avert large swings in blood glucose concentrations. A person with type 1 DM also is encouraged to consume a simple carbohydrate if his/her blood glucose level is less than 100 mg/dL. By eating a simple sugar, this will easily be absorbed and help to increase blood glucose concentrations. Individuals with type 1 DM should carry high-carbohydrate foods with them all the time, while exercising, in the car, and at work or play. Keeping a tube of icing with them is a way to ensure they can obtain sugar quickly, if needed. Icing in a tube is shelf stable and also can be placed between the cheek and gums of a person with type 1 DM who is experiencing hypoglycemia. They would not need to chew or swallow this for it to be effective. Of course, other items like glucose tablets and orange juice also can be used. A person who exercises and has type 1 DM should consume complex carbohydrates and lean protein sources, accompanied by the appropriate amount of healthy fats (e.g., monounsaturated and polyunsaturated fats) throughout the day to maintain blood glucose concentrations and to also preserve their glycogen stores for exercise (1-4).
PREVENTING LOW BLOOD GLUCOSE DURING EXERCISE
Moderate-to-intense activity may cause blood glucose levels to diminish for the following 24 hours after exercise. This is sometimes referred to as the "lag effect" of exercise. Although the "lag effect" can be a positive effect of exercise, blood glucose must be closely monitored before and after exercise, as well as throughout the day, to avoid hypoglycemia.
If blood glucose concentrations are less than 100 mg/dL immediately after exercise, one or more of the following can be done to prevent this from occurring in the future:
* increase carbohydrate intake before exercise
* decrease the dose of insulin for the subsequent exercise session
* consider decreasing the insulin dosage after exercise
* if blood glucose levels at bedtime are still less than 100 mg/dL, then increase the evening snack, perhaps even double the original snack, making sure that there is a mixture of carbohydrate and protein in that snack, and consume adequate fluids for proper hydration
The major goal is to prevent hypoglycemia as a result of exercise. To prevent postexercise hypoglycemia, here are some specific recommendations:
* Consume 15 g of carbohydrate if not planning to eat in the next 30 to 60 minutes before exercise.
* Take in 15 g of carbohydrate and 7 g of protein if not planning to eat for more than 1 hour before exercise (1-4).
These recommendations are only if a person does not have a lot of time to eat before exercising. Individuals with type 1 DM should consume a high-carbohydrate snack with fluids before exercise to avoid hypoglycemia and any possible dangers that can result if a person experiences hypoglycemia during exercise.
Contraindications to Exercise for People With DM
Despite the benefits of exercise for individuals with type 1 DM, contraindications to exercise do exist. If a person's blood glucose levels are greater than 250 mg/dL and ketones are present in their urine (ketonuria), he/she should not exercise. Caution should be used with exercise if ketones are not present and blood glucose levels are greater than 300 mg/dL. Further dehydration (with exercise) and ketone body buildup can result in ketoacidosis. In individuals with type 1 DM, ketonuria indicates a lack of insulin and the immediate need for an insulin injection. Exercise at this time would produce more ketone bodies and, thus, put this person in danger of ketosis and hypoglycemia.
It is recommended that all individuals with type 1 DM are evaluated by a physician before beginning an exercise program. They also should continue to monitor their blood glucose levels, maintain a healthy hydration status, and regularly see their physician for adjustments in their insulin and their registered dietitian for modifications in their food intake, particularly early on in the exercise program (4).
Individuals with type 1 DM require close monitoring of their blood glucose concentrations to avoid hypoglycemia. With close blood glucose monitoring, coupled with healthy and evenly distributed eating, hydration, and consistent exercise, a person with type 1 DM can usually be as active as a person without this chronic disease.
American Diabetes Association: http://www.diabetes.org/type-1-diabetes.jsp
Juvenile Diabetes Research Foundation International: http://www.jdrf.org/index.cfm?page_id=101982
1. Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Report of the expert committee on the diagnosis and classification of diabetes mellitus. Diabetes Care
26(Suppl. 1):S5-S20, 2003.
2. Alberti, K.G., P.Z. Zimmet. Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: diagnosis and classification of diabetes mellitus provisional report of a WHO consultation. Diabetic Medicine
3. Horton, E.S. Role and management of exercise in diabetes mellitus. Diabetes Care
4. Volpe, S.L., S.B. Sabelawski, C.R. Mohr. Fitness Nutrition for Special Dietary Needs
. Champaign: Human Kinetics, 2007.