Carbohydrate intake during exercise

During longer athletic events in particular (like marathons or triathlons), taking in extra carbohydrates during exercise helps maintain your blood glucose levels, enabling you to keep going at a faster pace for longer without getting too tired. But supplementing with carbohydrates even helps you perform better during intermittent, prolonged, high-intensity sports like soccer, field hockey, and tennis.

There is a limit to how many carbohydrates you should take in during exercise, however. Studies have shown that trained cyclists without diabetes can only digest and use about 80 grams of carbohydrate per hour while doing fairly hard cycling. Having higher levels of insulin in your body may increase your supplemental carbohydrate use a bit compared to someone without diabetes, but it’s unlikely to be by much when you consume carbohydrate during exercise because digestion is slower then due to greater blood flow to the muscles.

What types of carbohydrates should you consume during exercise? That depends on things like how long you’ll be exercising, the intensity of your workout, and what your blood glucose and insulin levels are before and during the activity. If you have to supplement to prevent hypoglycemia (mostly insulin users), aim to take in carbohydrates with a higher glycemic index (GI), like glucose gels, because they’re absorbed more rapidly and raise blood glucose levels more quickly. They’re also easier to digest during exercise than most with a lower GI, such as beans. (The glycemic index is a scale for measuring how fast the body digests carbohydrates; flip to Chapter 6 for more information.)

Even if you don’t routinely eat many high-GI carbohydrates, supplementing with them during activities is okay if you need them to prevent hypoglycemia or take some in during longer workouts or events.

High-GI carbohydrates you can use during exercise include sports drinks, sports bars, glucose tablets or gels, Gu, bagels, saltine or graham crackers, pretzels, hard candy, Smarties, and anything made with glucose or dextrose (another name for glucose). Any carbohydrates that are part of foods with a high fat content (such as potato chips or doughnuts) have a lower GI, will be absorbed much more slowly, and may not help you much during exercise.

People with type 2 diabetes who don’t take insulin or oral medications that cause insulin release are unlikely to need to supplement with any carbohydrates to prevent low blood glucose during most activities lasting less than an hour.

Normal daily carbohydrate needs

How many carbohydrates you should normally eat daily is hotly debated in the diabetes world. Your brain and nerves use about 130 grams of glucose daily as their primary fuel, so if you eat fewer carbohydrates than that every day, your body needs to convert some protein (or possibly fat) into glucose.

It’s also much harder to restore your muscle glycogen levels between workouts on subsequent days if you don’t eat at least 40 percent of your calories as carbohydrate (and eat enough calories in general). If you take in less than that, you’ll be more likely to develop hypoglycemia overnight and during subsequent workouts.

Your typical daily carbohydrates should likely be lower on the GI scale than your exercise ones to make managing your blood glucose levels at rest easier.

Exercise carbohydrates for insulin users only

The general recommendations for grams of carbohydrate intake in Table 7-1 are just a starting place and apply solely during activity (based on duration and intensity), not before or afterward. They assume that you haven’t taken any rapid-acting insulin recently for meals, snacks, or correction and take your starting blood glucose into account. People who don’t use insulin don’t need to take in exercise carbohydrates unless they do a really long event during which anyone — with or without diabetes — would eat or drink carbohydrates to supply extra fuels.

These carbohydrate intake recommendations also assume you’re not lowering your basal insulin doses before or during the activity, but you may need to do both (that is, eat more and lower basal and/or bolus insulin) for longer duration activities. Determining what works best for you in every situation takes some trial-and-error.

Recommendations from the American Diabetes Association used to, but no longer, tell people how many carbohydrate grams to consume. This change is a good thing because the amount varies on a case-by-case basis and depends on several different factors. For example, your blood glucose can be affected by how long you plan to exercise, what type of exercise you do, its intensity, and even how hot or cold it is. You should rely on testing your blood glucose and trying various amounts of carbohydrate to figure out what works for you with exercise as an added variable.

You have a lot to juggle when you take insulin and want to be physically active. Most exercisers who take insulin also eat something before prolonged, less intense activities, but not necessarily before weight training, sprinting, or other hard, shorter workouts. The time of day also makes a difference because doing early morning exercise may not drop your glucose like doing the same activity later in the day does. Depending on all these factors, your personal cutoff level to eat carbohydrate before exercise should be whatever you find works best for you. If your blood glucose is normal or slightly low before exercise, you may also want to take in 10 to 15 grams of moderate- or high-GI carbohydrate without any insulin coverage right when you start, especially if your blood glucose levels typically start to drop during the first 30 minutes of activity. If you’re wearing a pump, you may choose to use a temporary basal setting that lowers insulin delivery during exercise or even starting an hour or two before exercise, or possibly suspend your pump during exercise lasting an hour or less instead of eating. Or you may have to combine these strategies to prevent hypoglycemia.

If you’re able to set a lower temporary basal rate on your pump or have low levels of circulating insulin due to the time of day, you may not need to eat anything. If your insulin levels are high in your bloodstream during exercise (usually at a time within two to three hours after you took your last insulin bolus for meals, snacks, or hyperglycemia corrections), you’ll likely need to eat more to combat insulin’s glucose-lowering effects.

Some websites have recently attempted to create exercise “calculators” to estimate how many carbohydrates you need or how you need to adjust your insulin, but they generally can’t give accurate recommendations, given all the factors that can impact your blood glucose when you’re active. Getting a bad recommendation can often be worse than having no guidance at all, so do some trial and error on your own to figure out which adjustments you need to make. If you’re unsure how to make your own adjustments, check with your diabetes care team about which changes may work best for you, including possibly increasing your carbohydrate intake and reducing your insulin doses to prevent exercise-related hypoglycemia.

Keep these points in mind when it comes to changing your carbohydrate intake for exercise, if you use insulin or take pills that cause your pancreas to release insulin (sulfonylureas or meglitinides; jump to Chapter 3 for more information on these):

• When doing intense exercise (that makes it hard for you to talk during it), you may not need any carbohydrates during the activity, but watch out for hypoglycemia later.
• Competitions have more of a glucose-raising effect (especially when you’re nervous) than practices do, so check your blood glucose to see if you may need less carbohydrate.
• If you use a pump and reduce your basal rate prior to and during exercise, your carbohydrate needs may be significantly less.
• You may need extra carbohydrates before, during, and after activity (depending on intensity, duration, starting blood glucose levels, and so on).
• Consider whether you may need to consume some protein and fat after exercise and at bedtime to prevent lows later and overnight.
• Check your blood glucose more often after you experience a bad low or do hard exercise in the 24 hours prior to doing your latest workout.
• Doing new or unaccustomed exercise can cause hypoglycemia, both during and afterward, and you may need to take in more carbohydrates for that activity.
• If you take any insulin to cover what you eat within two hours after exercise, you’ll likely need less insulin than normal.
• Prevent the lows that can occur 6 to 12 (and up to 48) hours following exercise with a balanced intake of carbohydrates, protein, and fat.

Glycogen repletion and carbohydrates

Muscle carbohydrate stores of glucose (glycogen) are replaced at a rate of only 5 to 7 percent per hour after a workout. The rate is slightly faster when stores are low, but it slows down as they start to fill up. Insulin action starts to wane, too, as your muscles restore their glycogen stores. On a positive note, the sooner your glycogen is replaced, the less likely you are to develop late-onset hypoglycemia, which can occur up to a day or two later.

Not eating enough carbohydrate after exercise, or carbohydrate eaten without adequate insulin, may extend how long it takes your body to restore glycogen and result in late-onset hypoglycemia in insulin users.

After exercise, your muscles are using glucose to replenish themselves and continuing to burn calories, which can increase your risk of low blood glucose. Your risk for having a low afterward depends on what you did and which medications you’re taking, but you won’t know your risks unless you check your blood glucose levels to find out.

Especially if you use insulin, check your blood glucose within an hour of when you finish your workout and continue monitoring your levels at one-hour intervals for several hours to prevent lows or highs after exercise.

Take in adequate carbohydrate, along with sufficient (albeit likely reduced) insulin before, during, and after prolonged moderate- or high-intensity workouts to maintain and restore your muscle and liver glycogen and blood glucose. Doing so is especially important right after you finish exercising (within 30 minutes to 2 hours after).

Protein intake for everyone

Because protein is important to overall health but isn’t a major exercise fuel, you do need to worry about consuming enough, although it doesn’t have to happen right before or during an activity. You’ll get most effective restoration of liver glycogen if you keep your blood glucose levels in tight control after exercise. Consuming a small amount of protein along with carbohydrate (in a ratio of 1:4, or 1 gram of protein to every 4 grams of carbohydrate) after an activity may help you repair your muscles and get stronger more quickly.

Typically, an ounce of chicken, cheese, or meat has about 7 grams of protein.

Protein intake for insulin users

Taking in more protein and slightly less carbohydrate after exercise can help keep your blood glucose more stable over time because protein takes three to four hours to be fully digested, and some protein is converted into blood glucose. You can eat protein strategically to prevent later-onset hypoglycemia, which insulin users are more likely to get. Have some in your bedtime snack (along with fat and carbohydrate) to prevent nighttime lows after a day of strenuous or prolonged activity, if you use insulin.

Taking in some protein along with carbohydrate right after hard or long workouts may help your body replenish its glycogen stores more effectively.

Maximizing protein for training and aging

Though anyone who is getting older — and that includes all of us — can benefit from taking in enough protein, supplements are usually not the optimal way to get enough. Let me explain why.

As you get older, your body may need more protein compared to when you were younger to form, maintain, and repair muscles and other body structures. Anyone who is doing regular exercise training also needs more protein to repair and build muscle, but you can usually get this amount (and more) when you’re eating a balanced meal plan with adequate calories. To figure out how much you need, find the category that fits your age and training, and multiply your body weight (in pounds or kilograms) by the grams found in the corresponding Table 7-2 column.

The biggest myth about amino acid supplements, and protein in general, is that you must load up on them to gain muscle. That’s just not true. The protein requirement for strength-training athletes may be about twice as high as normal, but most people in the United States already consume more than these higher amounts of protein in their daily diets.

To put it in perspective, to gain one pound of muscle mass a week (a realistic maximum), a strength-training athlete needs no more than 14 extra grams of quality protein per day. You can easily get this amount from these sources:

• About two 8-ounce glasses of milk
• 2 ounces of lean meat, chicken, fish, or cheese (which isn’t much)
• Slightly more than two eggs (only the whites contain protein)

Adequate intake of protein also helps to maintain lean body mass when you lose weight on a diet and can help you gain more muscle mass from exercise training.

Fat use and intake for everyone

What effect does exercise training have on your body’s use of fat as a fuel? Though you potentially have become better at using fat during exercise with training, fat use depends on how hard you’re working out. If you work out at the same relative intensity before and after training (meaning that you pick up your pace as you get fitter and more trained), your fat use remains constant. Your body’s use of fat as a fuel during exercise only increases after training if you’re now working out at a relatively lower percentage of your maximal capacity (that is, the same pace as before training, even though you could now pick up the pace). Some evidence suggests that training while eating a lower carbohydrate diet with a higher fat content may increase your ability to use fat during the activity; however, relying on fat for fuel for the more serious athlete compromises speed.

Being physically trained does lower any fat-induced insulin resistance, which makes it easier for you to restore muscle glycogen after workouts.

Eating high-fat foods for exercise (that is, fat loading) may be detrimental to your performance and isn’t recommended. Also, any fat that you eat before and during exercise isn’t digested and ready for use for many hours and may slow the digestion of any carbohydrate that you eat.

How much or how little fat your body uses as a fuel during exercise doesn’t determine how much fat weight you lose from being active. Instead, it’s entirely dependent on how many calories you expend, not which fuel your body burns. Fueling activity with more fat overall makes you use less blood glucose, which is why training reduces the carbohydrates you need to keep your blood glucose stable while doing the same activity at the same intensity (pace) after training. Limit your intake of trans fats and highly processed fats for better health, though.

Strategic fat intake for insulin users

Your blood glucose may stay more stable overnight if you eat a bedtime snack with a higher fat or protein content, such as ice cream, yogurt, or soymilk, on days when you’ve been particularly active. Fat provides an alternative energy source for your muscles for many hours after you eat it and some protein is converted into glucose before that, but even having a high-fat meal with the carbohydrates held constant increases insulin needs. Taking in more protein generally includes insulin needs as well.

Fluids during exercise

Preventing dehydration without overloading on fluids is an individual balancing act. You shouldn’t be gaining weight during a physical activity. You’ll sweat and lose water in other ways, so your weight should go down (until you rehydrate). Replace only the weight that you’ve lost. After exercise, continue to use thirst as your guide, rehydrating after the fact with water or other fluids with no calories. If you must drink a lot of fluid during an activity, wait until you start to urinate before drinking any more.

For shorter physical activities (lasting an hour or less), plain water is fine unless you need some extra carbs to prevent hypoglycemia; then you can drink a sports drink like Gatorade or Powerade that contains some rapidly absorbed carbs. I discuss some of these other options in the later section “Using sports drinks, juice, and more.”

When you’re active, consuming excessive fluid can also be harmful. If you drink too much water and other fluids during exercise, you increase your risk of diluting the sodium content of your blood, potentially causing a medical condition known as hyponatremia, or water intoxication. This condition puts you at risk for seizures, coma, and even death. This condition is more common in distance events such as marathons, and more common in persons who are running slowly (in the back of the pack).

To avoid overhydrating, swig a mouthful (about 1 ounce, or 30 milliliters), and drink that amount every 10 to 15 minutes or so. If you don’t sense when you’re getting thirsty, just start drinking about 15 minutes into your exercise session. This strategy may vary somewhat if your blood glucose has been running high; I discuss that scenario in the following section.

You don’t need to worry about replacing electrolytes, like sodium, potassium, and chloride, unless you’re exercising outdoors in hot weather for more than two hours at a time; even then, you can usually wait to replace electrolytes naturally with your food the next time you eat. The exception to this is people who sweat a lot and lose sweat with a high salt content. If you can lick your lips and taste lots of salt, or have salt on your jersey when you finish your activity, you should consult with a sports dietitian to discuss your hydration and electrolyte strategy.

In general, the fluids you drink should contain less than 10 percent carbohydrates (that is, 10 grams of carbs per 100 milliliters of fluid) to promote faster emptying from your stomach. Cold fluids are absorbed more rapidly than lukewarm ones. Keep the total volume below 500 milliliters at a time, or it will slow the rate of emptying and increase your risk for water intoxication. During exercise, start drinking at least a small amount of fluids before you feel thirsty because thirst isn’t triggered until you’ve already lost 1 to 2 percent of your fluid body weight. Taking in a large mouthful (1 to 2 ounces) at a time usually suffices. The best way to stay hydrated during exercise with diabetes is to follow these guidelines:

• Drink cool, plain water during and following exercise, especially during warmer conditions.
• Take frequent breaks to have a chance to cool down, preferably out of the heat and direct sunlight.
• To know how much fluid to replace, weigh yourself before and after a prolonged activity and only replace the weight you’ve lost (1 liter of water equals 1 kilogram, or 2.2 pounds) and no more.
• If you prefer fluids with some flavor, try flavored waters or sports drinks that have no added carbohydrates or calories (with a pinch of salt to taste more like a sports drink).

What to do if your blood glucose is high

If you’re exercising with any elevation in your blood glucose, drink slightly more fluids than you normally would because you can more easily become dehydrated. Elevated blood glucose can cause you to pee out more water, so your risk of losing extra fluids is greater when your glucose has been running higher.

Exercising itself compounds the risk by increasing sweating (thus loss of water), which can rapidly compound a dehydrated state. Because exercising during hot weather can be especially dangerous for older individuals — who may not release heat as effectively as younger adults — adequate fluid replacement and frequent rest breaks need to be high priorities.

Having autonomic neuropathy (central nerve damage related to diabetes) can also compromise your ability to release heat and stay hydrated, so be more cautious and drink more fluids during exercise if you have this complication.

Using sports drinks, juice, and more

During longer workouts or a long sports event, supplementing with carbohydrates is key. During marathons or triathlons — and even intermittent, prolonged, high-intensity sports like soccer, field hockey, and tennis — taking in extra carbohydrate helps maintain your blood glucose levels, enabling you to keep going at a faster pace for longer without fatiguing. It also provides your muscles with an alternative source of carbohydrate (besides muscle glycogen).

With so many sport drinks, gels, and other sport-related supplements to choose from, how do you know which is best, if any? Simply keep in mind that more concentrated ones will not empty from your stomach or raise your blood glucose as quickly during exercise.

As far as food supplements go, it’s a personal choice. More people use ones with a balance of carbohydrate, protein, and fat during longer bouts of exercise, or they may just use glucose tablets or gels (even athletes without diabetes often do this). For workouts lasting less than an hour, you may not need any extra carbs in solid or liquid form.

Don’t fill your stomach with too many solid foods when your exercise level is going to be hard, or you may feel queasy or get an upset stomach.

Fruit juices are usually more concentrated than 10 percent. They’re not the best thing to take in during exercise, but if you do drink juice while exercising, add some water to it to dilute it so you can digest it faster. But remember that their glycemic effect is usually lower than many other choices. You may also want to avoid juice simply because drinks with high amounts of fructose (fruit sugar) may cause abdominal cramps or diarrhea. Fructose is absorbed more slowly than glucose and pulls water into your stomach when you consume it in high concentrations, especially during exercise.