By: Christopher D. Jensen, PhD, MPH, RD
Nutrition & Epidemiology Researcher
Sports Nutrition for Athletes with Type 1 Diabetes: Interplay of Diet, Insulin Therapy, and Exercise.
Diabetes directly impacts the fueling of muscles
When training and competing, our metabolic machinery works in high gear to meet the energy demands of contracting muscles. Fuel sources include glycogen and fat droplets in muscle, fats from adipose tissue stored in places such as the waist and hips, and glucose that is either made in the liver from protein or obtained from glycogen stores in the liver. Behind the scenes, this energy-sustaining metabolic interplay is under the control of hormones, with insulin being a key one.
Insulin is produced in the pancreas and it’s considered an anabolic hormone because it allows the cells in the body to take up glucose and store it in the form of glycogen as you recover after exercise. It also promotes the storage of glycogen in the liver and inhibits the release of glucose from the liver. In addition, insulin inhibits the release of fats from your adipose tissue reserves and promotes the synthesis of proteins, including the proteins found in muscle.
Insulin is in a tug-of-war relationship with other hormones that are catabolic, or act opposite to it. These counter-regulatory hormones stimulate the breakdown of glycogen in the muscle and liver into glucose that can be used as fuel. They also allow fats to be released from stored adipose tissue and glucose to be made in the liver from proteins, so they too can be used for fuel. The back and forth between the anabolic effects of insulin and the catabolic effects of these other hormones is what allows an athlete to run 10 miles in the morning, and then to recover afterwards so that he or she can do it again tomorrow.
But diabetes throws a wrench into these metabolic machinations. With type 1 diabetes, you are unable to produce insulin due to destruction of the cells in the pancreas that produce the hormone. As a result, regular insulin injections are needed to simulate what the pancreas would be doing if it could make insulin.
Insulin therapy is a balancing act
The interplay between insulin therapy, diet, and exercise is extremely important to athletes with diabetes. The goal is to match the type, amount, and timing of insulin to food intake and activity level. Regular monitoring of blood glucose levels is critical to ensuring that appropriate amounts of insulin are provided and metabolic complications are avoided. When insulin levels are not in balance with need, abnormalities in blood glucose and acid concentration can occur:
Hypoglycemia, or low blood sugar, is the most common adverse event associated with insulin therapy. An excess of insulin in comparison to need causes large amounts of glucose to be taken up by cells and too little glucose to be released from the liver. As a result, the blood glucose level drops too low. Symptoms include sweating, shaking, nausea, rapid heart rate, drowsiness, confusion, and poor coordination. If low blood sugar goes untreated, the individual can go into a hypoglycemic coma, which if allowed to progress can be fatal. For this reason, athletes with type 1 diabetes are encouraged to exercise with a partner or coach who is familiar with the symptoms and treatment of hypoglycemia.
Hyperglycemia, or elevated blood sugar, is the other side of the coin. This can occur when there is too little insulin available. When this happens, cells can’t take up glucose from the bloodstream and too much glucose is released by the liver. As a result, blood sugar levels rise too high. Symptoms of hyperglycemia include thirst, fatigue, difficulty concentrating, drowsiness, nausea, and muscle cramping. Over the long term, having sustained periods of elevated blood glucose increases the risks of kidney disease, problems with eye health, and cardiovascular disease.
Ketoacidosis, or a high level of ketones in your blood, can occur, along with hyperglycemia, when there is too little insulin available. Without adequate insulin, your cells don’t get the glucose they need for energy. Instead, your body burns fat for energy, which produces ketones as a by-product. Ketones are acids that build up in the blood and appear in the urine. A buildup of ketones is a warning sign that your diabetes is out of control. This is a serious condition that can lead to diabetic coma or even death, so it requires urgent medical attention.
Exercise further complicates the metabolic picture
Muscle contraction during exercise causes the body to be more responsive to insulin during exercise and for a period after exercise. In addition, when muscles contract they can take up some glucose from the bloodstream without an assist from insulin. Typically, this translates to a reduced requirement for insulin during exercise, often by 50–80%. If this adjustment is not made, insulin levels may be too high or too low during exercise. If insulin is too high, there will be inadequate fuel available to meet the demands of training or competing, and you can develop hypoglycemia. If your insulin level is too low, the liver produces extra glucose and releases it into the bloodstream, but cells are unable to take up the glucose. As a result, blood sugar and possibly ketone levels rise, with potentially serious consequences if not dealt with immediately. By adjusting your insulin dose depending on the length and intensity of exercise, control of blood glucose level can be enhanced. This is a subject you’ll want guidance on from your physician.
Effect of diabetes on dietary needs
Blood glucose control in athletes with type 1 diabetes is usually better when exercise patterns and eating patterns, including meals and snacks, are consistent. In general, athletes with diabetes have the same dietary requirements as athletes without the condition, including plenty of vegetables, fruit, beans, breads, and cereals; moderate amounts of fish, meat, poultry, eggs, and dairy products; and smaller amounts of refined sugar, alcohol, and foods high in fat. Needs for energy, carbohydrates, protein, and fat are as follows:
- Athletes with type 1 diabetes need to consume enough food for energy in order to stay healthy, maintain a desirable body weight, and train and compete effectively. This includes making adjustments when the intensity and/or duration of exercise changes.
- Carbohydrates are needed on a daily basis to maintain blood glucose levels and to replace glycogen stores. The recommended range for athletes is typically 2.7–4.5 grams/lb (6–10 grams/kg).
- Protein intake recommendation for both endurance and strength athletes with diabetes is 0.5–0.8 grams/lb (1.2–1.7 grams/kg).
- After carbohydrate and protein needs are met, healthy sources of fat can provide the remaining caloric needs. Healthier sources of fat include monounsaturated and polyunsaturated fats from plants, such as vegetable oils, nuts, seeds, and avocados.
Including carbohydrate-containing foods with a low glycemic index can assist with blood glucose control. Glycemic index is a tool used to rank foods according to their immediate effect on blood glucose levels. Carb-containing foods that are broken down quickly will rapidly release glucose into the bloodstream. These are known as high glycemic index foods. Those that break down slowly gradually release glucose into the bloodstream. These are known as low glycemic index foods, and this latter category can be advantageous for those with diabetes.
Examples of low glycemic index foods include:
- Fresh fruit — apples, bananas, pears, and grapes
- Breads and cereals made with whole grains
- Whole-grain hot cereals such as oatmeal
- Whole-grain pasta
Along with selecting healthy foods, monitoring food portions is also important in managing blood glucose levels.
Practical Strategies for Managing Diabetes Before, During, and After Exercise
Before training and competing
Hydration — You’ll benefit from starting workouts and competitions fully hydrated. Consuming 14–20 fl oz (400–600 ml) of water or sports drink (note that not all sports drinks are carb free) 2–3 hours before exercise can help make up for any fluid deficits left over from prior workouts. Also, hydration status before exercise can be monitored by checking urine color. A light-yellow color is generally consistent with adequate hydration. If urine is darker, like the color of apple juice, that’s often a sign that more fluids are needed.
Pre-exercise eating — Consuming a meal 2–4 hours before training or competing can help top off muscle and liver glycogen fuel stores. The meal should be composed of familiar and well-tolerated carbohydrate foods and beverages. Slow-to-digest fatty and high-fiber foods should be avoided in the pre-exercise meal. Carbohydrate-rich foods include pasta, rice, bread, cereal, vegetables, fruit, and dairy products such as yogurt and milk. For some athletes, the pre-exercise meal may need to be followed up with a small snack closer to exercise. Check blood sugar before exercise — it’s important to ensure that your blood glucose concentration is at an appropriate level before starting exercise. Exercising with a high blood glucose concentration — hyperglycemia — disrupts normal metabolic control and will elevate glucose levels even further. Starting with a low blood glucose level should also be avoided. Use the table below as a guide for what to do with your monitoring result. However, you should also discuss this with your physician or sports nutritionist, since the appropriate action can be more complicated depending on what activity you are embarking upon.
Blood glucose control is often tighter if a consistent training routine is followed. It’s more difficult in situations when the start time of a competition is unknown or the length of an event varies. Knowing about and remaining vigilant to the development of symptoms of hypo- and hyperglycemia, and regular monitoring of blood sugar, are necessary in these situations. The same is true for elevated ketones in the bloodstream and the need for monitoring urine ketone levels.
Pre-competition jitters — A side effect of the nerves associated with a competition is the release of hormones such as adrenalin and cortisol. These hormones stimulate the release of glucose from the liver and reduce the effectiveness of insulin. This can alter blood glucose levels.
To minimize the effects of pre-competition nerves, consider the following:
- Implement your competition-day preparation and nutrition strategies during training.
- Practice comforting techniques such as breathing exercises, muscle relaxation, listening to music, and talking with a sports psychologist.
- Talk with your physician about the possibility of taking slightly more insulin on the day of a competition or using a more intensive insulin routine such as more frequent and smaller doses of short-acting insulin.
- Avoid decreasing carb intake on the day of a competition in order to reduce blood glucose level. This could lead to insufficient energy intake for the competition. Planning and practice can help avoid this situation.
Travel — If you are traveling to a destination for an event or to train, pack ample supplies of insulin and testing equipment in a container that protects against heat stress and physical damage. Consider carrying half your supplies in your hand luggage and the rest in your checked baggage.
During training and competing
Hydration — Dehydration can impair your ability to train or compete when 2% or more of body weight is lost during exercise due to fluid loss. To stay hydrated during exercise, consume fluids at a rate that matches your sweat rate. This generally requires approximately 13–26 fl oz (400–800 ml) every hour during exercise, preferably in smaller amounts taken frequently. However, fluid needs vary considerably. Clicking on the Sweat Rate Calculator at PowerBar.com provides access to a step-by-step guide to calculating sweat rate. For exercise lasting an hour or longer, or in the heat or humidity, a sports drink that provides sodium and carbohydrates is typically preferred over plain water. For shorter sessions in moderate conditions, plain water is usually adequate for hydration purposes.
Fueling — Carbohydrate intake during exercise should be considered when moderate-to-high-intensity exercise exceeds an hour in length. Approximately 30–60 grams of carbohydrates for exercise lasting 1–2 hours is typically recommended, and it’s generally not necessary to have extra insulin if carbs are consumed during exercise. A sports drink that provides fluid along with carbs is a convenient option for most exercise situations. Other fueling options include energy gels and energy bars. When carbs are needed, consuming small amounts frequently is preferred over large amounts taken all at once. You might consider reviewing the ingredients and nutrition information of any new fueling options with your doctor or nutritionist.
Practice it first — It’s prudent to trial new fueling and hydration strategies during training sessions, when it’s easier to monitor effects on blood glucose control.
Know what to do about hypoglycemia — Athletes with type 1 diabetes should exercise with a partner or coach who is familiar with the symptoms and treatment of hypoglycemia. If hypoglycemia occurs, exercise should be stopped and the athlete given approximately 15 grams of quickly absorbed carbohydrates such as ½-cup of fruit juice, 6 fl oz of regular (not diet) soda pop, 8 fl oz of low-fat milk, or 4 glucose tablets. An energy gel is also a quick and convenient way to take in carbs if hypoglycemia develops during exercise. Blood sugar should be monitored every 15 minutes until it rises above 80 mg/dl. Severe hypoglycemia requires prompt medical intervention.
After training and competing
Make recovery a priority — Recovery strategies are generally the same for athletes with and without diabetes. That means fluids and sodium are needed for rehydration, carbs are needed to replenish muscle and liver glycogen stores, and protein is needed for the repair and building of muscle tissue in response to exercise.
Rehydrate — Fluid lost during exercise should be replaced by gradually drinking 16–24 fl oz (460–680 ml) of a recovery beverage, sports drink, or water for every 1 lb (0.45 kg) of weight lost. Rehydration will be more effective when sodium is included with the fluids and food that are consumed during recovery.
Muscle repair and building — Taking in 10–20 grams of protein as soon as possible after exercise will provide the amino acid building blocks needed for repairing muscle tissue and for making new muscle tissue as an adaptation to training.
Replenish glycogen stores — To promote glycogen restoration after exercise, consume about 0.5 grams of carbohydrates per lb (1.1 grams per kg) body weight within 30 minutes of finishing exercise and repeat this within 2 hours, or resume regular meals and snacks with carbohydrates. It’s also possible that individuals with diabetes have a reduced ability to store glycogen after exercise. This should be a consideration when strenuous training sessions or competitions are held less than 24 hours apart. Keep in mind that if you are using a sports drink to rehydrate, you may be getting carbohydrates that should be accounted for.
Be aware of the risk of delayed hypoglycemia — The increased insulin sensitivity caused by exercise can last for several hours after exercise. This can raise the risk of hypoglycemia for up to 48 hours after exercise is completed. Preventing delayed hypoglycemia requires consuming sufficient carbs before, during, and after exercise. It may also be necessary to reduce the next insulin dose after exercise. Delayed hypoglycemia may occur during the night and can exacerbate fatigue. The heightened risk of hypoglycemia after exercise underscores the need for diligent blood glucose monitoring after exercise sessions.
Recovery before alcohol — Be aware that alcohol inhibits the release of glucose from the liver and increases the chance that hypoglycemia will occur. Consuming excessive alcohol also impairs the ability to recognize hypoglycemia symptoms. Athletes are encouraged to ensure that their recovery needs are taken care of first, and to moderate their alcohol intake after exercise if alcohol consumption is allowable.
Effective carbohydrate loading requires that insulin administration be adjusted to account for an increase in carbohydrate intake and the effects of an exercise taper. Carbohydrate loading should be considered only if you have good diabetic control. Also, regular blood glucose monitoring is essential when carbohydrate loading.
Strength sports such as martial arts and lifting weights often require short, repetitive, and intensive bursts of activity. This type of exercise can cause an adrenalin response that temporarily raises blood glucose levels. It’s not known whether this temporary hyperglycemia has any long-term deleterious effects, and managing this response can be difficult. For example, decreasing carbohydrate intake in an attempt to avoid hyperglycemia might jeopardize performance during exercise and increase the risk of delayed hypoglycemia after exercise. Also, increasing your insulin dose after exercise to reduce blood glucose concentrations may increase the risk of delayed hypoglycemia once the adrenalin response has worn off. Monitor your blood glucose regularly so you’re aware of how your body responds to strength exercise. Finally, work with your physician to seek guidance on the best way to manage your response to this type of exercise.
Use a training diary
A training diary can be a very useful tool. You can also record the results of your blood glucose testing in your diary, so you can monitor both diabetes and non-diabetes-related factors simultaneously. You can create your own training diary on a spreadsheet, using the category headings suggested below. Collecting this information allows you to identify problem areas and to take steps to rectify them. Record the information even when things are going well; that way, if you are going through not-so-good times, you can look back on strategies that have worked for you before. Use your own codes and short descriptions to reduce the amount of time required to fill out the diary. Show your diary to your physician, coach, and/or sports nutritionist, when needed, to help you achieve your athletic goals and effectively manage your diabetes.