Chapter 7
IN THIS CHAPTER
Focusing on eating the right foods to be active
Taking in carbohydrates, protein, and fat as needed
Maintaining proper hydration for good health and exercise
How well you fuel your body with food is a big deal when you’re physically active. So are staying hydrated when you’re exercising and refueling effectively after exercise. Doing all these things with diabetes as an added variable can be complicated, so the foods you eat can impact your body's response to physical activity. Knowing when and how to adjust your food intake before, during, and after exercise is important for keeping your blood glucose levels as close to your target range as possible. This is not always an easy feat to accomplish, but it does help if you understand more about how the macronutrients (that is, carbohydrates, protein, and fat) are metabolized and how quickly they are available for your body to use.
In this chapter, you discover how carbohydrates, protein, and fat play different roles in helping you achieve your exercise (and blood glucose) goals. Protein is critical for rebuilding muscles and maintaining strength as you age, and you find out how much you really need on a daily basis. On the other hand, fat isn’t as important during all activities as you may think, so this chapter helps you focus on taking in adequate carbohydrates and making sure your fluid intake will keep you going. If you’re a coffee lover, I also have some good news for you related to coffee and exercise.
The most important energy source for all types of exercise is carbohydrate. At rest, your body typically uses about 60 percent fat and 40 percent carbohydrate. When you reach an exercise intensity harder than an easy walk, your body switches to higher carbohydrate use (even if your cardio machine says you’re in a “fat-burning range”).
During exercise, your body uses a combination of carbohydrates available in your blood (glucose), muscles (muscle glycogen), and liver (hepatic glycogen). Any carbohydrates you eat are converted to blood glucose within five minutes to two hours. If you run low on carbohydrates during an activity, you’ll have to slow down, you may “hit the wall” (and have to stop), or you may get low blood glucose. Eating a chronically low-carbohydrate diet can make it difficult for you to participate in an exercise that is hard or long at your highest potential level, but supplementing with carbohydrates during any activity helps you maintain your blood glucose.
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.)
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.
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.
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.
TABLE 7-1 Recommended Carbohydrate Intake for Exercise (Grams) Based on Duration, Intensity, and Starting Blood Glucose
Duration |
Intensity |
Starting Blood Glucose under 100 mg/dL |
Starting Blood Glucose 100 to 149 mg/dL |
Starting Blood Glucose 150 to 200 mg/dL |
Starting Blood Glucose over 200 mg/dL |
30 minutes |
Low |
5–10 |
0–10 |
None |
None |
Moderate |
10–25 |
10–20 |
5–15 |
0–10 |
|
High |
15–35 |
15–30 |
10–25 |
5–20 |
|
60 minutes |
Low |
10–15 |
10–15 |
5–10 |
0–5 |
Moderate |
20–50 |
15–40 |
10–30 |
5–15 |
|
High |
30–45 |
25–40 |
20–35 |
15–30 |
Adapted from Colberg, S. Diabetic Athlete’s Handbook, Human Kinetics, 2009.
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.
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.
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.
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 is never a key exercise fuel, but it’s critical for other reasons. During most exercise, protein contributes less than 5 percent of the total energy, although it may rise to 10 to 15 percent during a prolonged event like a marathon or Ironman triathlon. Taking in enough dietary protein is important because dietary protein allows your muscles to be repaired after exercise and promotes the synthesis of hormones, enzymes, and other body tissues formed from amino acids, the building blocks of protein. You should consume at least 12 to 35 percent of your daily calories as protein. For most people this means taking in at least 60 grams of protein daily.
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.
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.
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.
TABLE 7-2 Recommended Protein Intake by Training Status and Age
Per Pound Body Weight |
Per Kilogram Body Weight |
|
Adults 19 to 50 years (inactive) |
0.36 grams |
0.8 grams |
Adults over 50 years (inactive) |
0.5 grams |
1.1 grams |
Endurance training |
0.55–0.64 grams |
1.2–1.4 grams |
Strength training |
0.68–0.77 grams |
1.5–1.7 grams |
Calorie deprived (diets) |
0.73–0.82 grams |
1.6–1.8 grams |
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:
Although carbohydrate is the main energy source during exercise, fat is an important contributor, particularly during low-intensity or slower, prolonged activities like walking the dog or taking an all-day hike. It’s also the main fuel that your body uses to keep your metabolism humming along during recovery from your latest workout. However, the body hardly uses fat at all during high-intensity aerobic and anaerobic exercise, both of which rely on carbohydrates for energy.
Your body has almost unlimited stores of fat, even if you’re lean. However, consuming fat before or during exercise doesn’t alter your body’s use of stored carbohydrates. Taking in fat after exercise can help keep glucose higher later on because fat takes up to five to six hours to fully digest. When the digested fat that you ate earlier hits your bloodstream, you’ll be more insulin resistant, which helps keep your blood glucose from dropping.
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.
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.
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.
Do you need that cup of steaming java in the morning to start your day off right (or just to feel awake)? If so, you’re not alone, and you’re probably drinking it more for the effects of the caffeine than any other reason. Caffeine is a stimulant found naturally in coffee, tea, cocoa, and darker chocolates that stimulates the central nervous system and increases wakefulness. It also increases your body’s release of adrenaline, which can mobilize stored fat and provide an alternate fuel to your exercising muscles.
Some people find that exercising feels easier with caffeine use. It’s great for directly stimulating the release of calcium in muscles to increase the strength of your contractions. Feeling stronger or less fatigued is likely the most important effect as far as exercisers are concerned. It potentially increases performance in almost any event or physical activity that you choose to do, be it long or short, intense or easy.
A major concern of using caffeine is that taking in too much of it may increase your insulin resistance, but it’s also likely that any such effect will be minimized during your actual workouts. When you get caffeine naturally through coffee, it may have less of an impact on insulin action than straight caffeine does (likely due to other compounds found in coffee). But the latest research shows that coffee may still raise your blood glucose (if you’re not exercising), so watch how much you drink when you’re just sitting around and not being active.
Another potential downside of caffeine is that it can exert a diuretic effect, meaning that when you consume caffeinated beverages while at rest, you may lose more water by urinating more than when drinking noncaffeinated drinks. Any caffeine you consume right before or during exercise has a minimal diuretic effect, however, so you don’t have to worry about becoming dehydrated from using it then because it won’t make you lose extra water during activities. The idea that caffeinated drinks will hydrate you less well than caffeine-free ones is only a myth, but this only applies to any drinks you take in during the activity. But too much caffeine can cause your bones to thin and decrease how well your insulin works, along with increasing your anxiety levels, heart rate, and risk for abnormal heart rhythms, so choose decaf options at least some of the time. You may also want to limit your intake to one large cup of coffee (containing about 150 milligrams of caffeine) before events to be on the safe side.
Adequate fluid intake is essential to living well and feeling your best at any age. As you grow older, you may lose some of your normal thirst sensations, putting you at risk for dehydration unless you make a conscious effort to drink more. Adequate fluid intake is also by far the best constipation cure out there.
As a person with diabetes, you may have special concerns related to hydration. Many recommendations over the years have suggested people should drink at least eight 8-ounce glasses of fluid daily; however, this recommended amount hasn’t been scientifically tested and you may need less if you’re getting other fluids from the foods that you eat. If you simply drink when you’re thirsty during the day, most of the time you’ll stay hydrated. This works well until you’re older and potentially lose your early thirst sensation with advancing age.
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.”
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.
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.
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.
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.
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