Exercise and Sport in Diabetes, 2nd Ed.: What Is Exercise?

Whatever the intensity and duration of exercise, optimum control of diabetes can only be achieved with careful planning and a good training and nutritional strategy....

Regular physical activity, diet and insulin are the cornerstones of diabetes management. The management of blood glucose levels poses a challenge for people with diabetes undertaking sport or exercise. They must have an understanding of basic food composition and know how the body regulates its fuels before, during and after exercise in order to successfully manage blood glucose levels.

Hypoglycemia is a real risk to people with type 1 diabetes and especially those taking part in hazardous sports such as water sports and rock-climbing where a 'hypo' can potentially be fatal. Hyperglycemia can significantly affect performance, leading to fatigue. The management of blood glucose levels is therefore an important goal and having a good nutritional strategy is an essential component of exercise management.

3.3 Nutritional Principles for Optimizing Sports Performance

The International Olympic Committee (IOC) Medical Commission Working Group on Sports Nutrition has recently reviewed the key issues in sports nutrition.¹ The nutritional principles for optimizing exercise performance are very similar to the nutritional recommendations for diabetes.² The basic dietary requirements for energy, protein, fat, carbohydrate, vitamins and minerals are no different from a non-diabetic athlete.³ The skill is to identify when changes in insulin and/or carbohydrate are required to optimize blood glucose control for exercise, training, and competition.

People eat food not nutrients. The skill of a dietician is to translate the nutritional goals into an eating plan which takes into account people's food preferences and lifestyle issues. Food availability, cooking skills, financial and social considerations, timing of exercise in relation to food intake and nutritional knowledge must be considered. Athletes with type 1 diabetes need to incorporate all of these factors in combination with their current insulin regimen and predicted blood glucose response to exercise.

When planning a nutritional strategy there are two main issues to consider: first, identification of the nutritional goals and second how these goals are to be achieved in practice.

• What are the energy requirements? Does energy intake match energy output? Are weight changes required?
• What is the macronutrient composition of the diet? Does an athlete require additional protein or need to reduce fat intake?
• Are the micronutrient needs being met, particularly iron and calcium?
• Are dietary supplements being used?
• What are the fluid requirements? Are sports drinks being used?

Energy balance is not the objective of athletic training. To maximize performance, athletes strive to achieve an optimum sports-specific body size, body composition and mix of energy stores. Marathon runners require energy for endurance but do not want to carry excess body weight. Similarly, gymnasts need energy for strength but may also need to lose weight, and weight-lifters need energy to increase muscle bulk and strength.

Total energy intake must be sufficient to meet the increased energy expenditure during exercise. However, where a low body weight is advantageous or where an athlete is required to 'make weight', e.g. judo, food intake and therefore nutrient intake may be restricted. In females particularly, this can lead to problems with bone and reproductive health.

During training and competition, in sports of high intensity and long duration, the limiting factor for performance is energy intake, especially carbohydrate intake.

• The amount of energy needed depends on the intensity, duration and type of exercise undertaken.
• Total energy requirements will depend on age, sex and body weight.
• Young sports-people need additional energy for growth and development.
• Where there is a need to reduce body weight, this should be done gradually by following a sensible weight loss program.

Carbohydrate is the most important nutrient for working muscles. It fuels the training to optimize sports performance. Carbohydrate is stored as glycogen in the liver and muscles but stores are limited. During exercise, particularly high intensity exercise such as sprint training and team sports, e.g. football, hockey, these stores are rapidly depleted. A high-carbohydrate diet, together with sufficient insulin, will ensure these stores are replenished prior to the next exercise session. If stores are not replenished, the quality of training will be sub-optimal, fatigue may occur and performance will be affected.

Previous guidelines have recommended intakes of 60-70 per cent of total energy intake for athletes.⁵ However, a review of dietary surveys of athletes found their intakes to be 50-55 per cent of energy.⁶ It is now recommended that guidelines should be given as grams relative to body mass.⁷ Carbohydrate recommendations for training are given in Table 3.1.

Using these figures and the body weight, the total carbohydrate requirement can be calculated:

Body weight (kg) x Carbohydrate for level of training = Total carbohydrate requirement per day

Example: 60 x 5-7 (moderate duration, low intensity) = 300-420 g day^-l

Once the carbohydrate requirements have been estimated, suitable food choices can be made to meet these requirements. Appendix 1 gives some examples of carbohydrate content of some foods. In addition, most food labels will have carbohydrate content per 100 g of food (or per 100 ml if liquid) and some will give the amount per serving. However, it is important to be aware that the individual serving size may differ from the information on the label, particularly energy requirements are high. The total carbohydrate of the serving size will then need to be calculated.

The distribution of carbohydrate intake throughout the day will depend on the insulin regimen as well as timing of exercise, e.g.:

• short-acting analogues vs human soluble insulin;
• long-acting analogues vs intermediate or long acting insulins;
• twice daily mixtures vs multiple daily injections (MDI) vs continuous subcutaneous insulin infusion (CSII/insulin pump therapy).

People on MDI or CSII may find it easier to control blood glucose by adjusting insulin doses to carbohydrate intake and exercise. Programs have been developed to help to teach people the skills they need to do this.^9,10

The glycemic index (GI) is used as a measure of how quickly foods that contain carbohydrate raise blood glucose levels. The greater the rise in blood glucose, the higher the GI value. Generally foods are grouped under three categories: low, moderate and high. Foods with a high GI tend to cause a sharp rise in blood glucose levels. Low GI foods produce a more gentle rise in blood glucose levels.

Although a variety of tables of GI values for food have been published, they can only be used as a guide. This is because the GI can be affected by a number of factors, e.g. variety, brand, country of origin, method of cooking, degree of processing and the content of the previous meal. A food could have a high rating in one table and a moderate rating in another.

Studies in non-diabetic athletes found greater glycogen storage during 24 h post-recovery when high GI foods were consumed.¹¹ In people with diabetes, the total amount of carbohydrate has a much greater influence on glycemia than the source or type of carbohydrate.² More research is required before recommendations can be made on the use of GI, particularly as the majority of current evidence is based on studies with non-diabetic, non-exercising individuals.

1. International Olympic Committee. Sports nutrition. J Sports Sci 2004; 22(1): 1-146.
2. Diabetes UK. The implementation of nutritional advice for people with diabetes. Diab Med 2003; 20: 786-807.
3. Colberg S. The Diabetic Athlete. Leeds: Human Kinetics, 2001.
4. Loucks AB. Energy balance and body composition in sports and exercise. J Sports Sci 2004; 22: 1-14.
5. Devlin JT, Williams C (eds). Final consensus statement: foods, nutrition and sports performance. J Sports Sci 1991; 9 (suppl.): iii.
6. Burke LM, Cox GR, Cummings NK, Desbrow B. Guidelines for daily carbohydrate intake: do athletes achieve them? Sports Med 2001: 31: 267-299.
7. Burke LM, Kiens B, Ivy JL. Carbohydrates and fat for training and recovery. J Sports Sci 2004: 22: 15-30.
8. Stear S. Fuelling training and recovery. In Fuelling Fitness for Sports Performance. The Sugar Bureau, 2004; 33-5l.
9. DAFNE Study Group. Training in flexible intensive insulin management to enable dietary freedom in people with type I diabetes: Dose Adjustment for Normal Eating (DAFKE) randomized controlled trial. Br Med J 2002: 325: 746-749.
10. Everett I, Jenkins E. Kerr D, Cavan DA. Implementation of an effective outpatient intensive education program for patients with type I diabetes. Pract Diabet Int 2003: 20(2): 51-55.
11. Burke LM, Collier GR, Hargreaves M. Muscle glycogen storage after prolonged exercise: the effect of glycemic index of carbohydrate feedings. J Appl Pin sial 1993; 75: 1019-1023.

Fully updated to reflect the progress and understanding in the field, the book features new chapters and material on insulin pump therapy and exercise, physical activity and prevention of type 2 diabetes, dietary advice for exercise and sport in type 1 diabetes, and fluid and electrolyte replacement.

For more information on this book and how to get a copy, just follow this link to Amazon.com, Exercise and Sport in Diabetes (Practical Diabetes), Dinesh Nagi 2^nd Edition.

Copyright © 2010 by Blackwell Publishing Ltd, UK