IN THIS CHAPTER
Looking at digestion speeds
Comparing the glycemic index and glycemic load
Making modifications to improve blood-glucose outcomes
Strategizing insulin solutions when fat delays digestion
Managing carbohydrate intake is an important part of managing diabetes. While basic portion-control methods work well for some people, others rely on detailed carb counting to calculate mealtime insulin doses. Carb portioning and counting are key concepts, but the next layer is to understand how digestion rates differ among foods and how that influences blood-glucose levels.
This chapter moves beyond the basics in Parts 1 and 2 and explores other dietary variables that affect blood-glucose outcomes. Not all carbs are created equal. As carbs are digested, glucose becomes available. Whether the glucose races into the bloodstream or enters gradually depends on how long it takes for the food to digest. It may take ten minutes or it may take five hours, which makes a big difference. Fast digestion can result in a sharp rise in blood glucose. Very slow digestion may cause blood-glucose levels to rise hours after the meal.
The concepts in this chapter apply to everyone with diabetes, whether or not medications are used. Blood-glucose levels are simply easier to control if you understand the variables that influence digestion and absorption of food and then use that information to your advantage. Carbs and meds are two big pieces of the diabetes puzzle, and it’s crucial that those two pieces fit together.
If you take insulin, you need a firm grasp of how that insulin works. See Chapter 6 to review the specifics on insulin action times. You’ll want to make sure your insulin action matches the digestion timing of your meals. Discuss your insulin regimen questions with your healthcare provider.
Comparing Digestion Speeds for Fluids and Foods
This section identifies key factors that alter the rate of digestion and ultimately the absorption of the carbs in a meal. Blood-glucose levels reflect not only the amount of carb you eat but also the type of carb you choose.
Looking at liquid carbs
Liquids move through the stomach and into the intestine quickly. Therefore, sugary beverages can raise blood-glucose levels sharply. Sodas, juices, smoothies, milkshakes, specialty coffee drinks, and other sugar-sweetened beverages can derail blood-glucose management efforts. This is especially true if you have insulin resistance, as is the case with type 2 diabetes. See Chapter 11 for tips on choosing best-bet beverages.
High-carb beverages are rapidly digested and absorbed, so blood-glucose levels rise within minutes. If you polish off a bottle of soda or juice, the carbs from the drink will likely reach the bloodstream before the peak effect of injected insulin. The rapid-acting insulins peak in about one hour, and the duration of action is about four hours. That means the insulin works far longer than the digestion timing of the liquid carbs consumed. Beverages that are concentrated in carbs tend to cause a blood-glucose spike initially, but hypoglycemia may occur later. It can be hard to predict.
For the most part, it’s best to avoid sugary liquids. An exception to the rule is if you’re experiencing hypoglycemia. A blood-glucose level that falls below 70 milligrams per deciliter (mg/dl) is considered too low. Hypoglycemia indicates an imbalance in medication, activity, and carb intake. Drinking 4–6 ounces of fruit juice or regular soda is an appropriate choice for treating hypoglycemia. Exercise is another time when controlled amounts of liquid carbs can be used to fuel muscles during prolonged or strenuous exercise. For more on exercise, turn to Chapter 14 .
Singling out sugars
One tablespoon of sugar, honey, or syrup contains almost 15 grams of carbohydrate. For perspective, that’s the same amount of sugar as a whole cup of cantaloupe. Sugars and syrups have nearly 60 grams of carb in ¼ cup. The carbs in sugars add up quickly. Desserts and treats typically contain a lot of sugar, so controlling portion sizes is important.
As described in Chapter 3 , sugar is a simple carbohydrate. Its effect on blood glucose depends on the amount of sugar consumed and what the sugar is mixed with:
· Candies that are pure sugar digest quickly so they can raise blood-glucose levels swiftly. Examples of pure-sugar candies are jelly beans, gummy bears, and hard candies. These types of candy can be used to recover from hypoglycemia because they are digested and absorbed within 10–15 minutes.
· Candy that contains fat or nuts, such as a candy bar, is digested and absorbed more slowly. Chocolate and nuts are both high in fat. Fatty foods are retained in the stomach longer, as described later in this chapter. Slower digestion and absorption means blood-glucose levels tend to rise less sharply. Chocolate candies can take well over an hour to be digested completely. For this reason, chocolate isn’t the best choice for treating hypoglycemia.
See Chapter 15 to find out more about the causes, symptoms, and effective treatment of hypoglycemia.
Figuring out fruit
Fruit offers health benefits and should be consumed as part of a balanced diet. However, the natural sugars in fruit tend to raise blood-glucose levels sharply if eaten in excess. There’s no starch, protein, or fat in fruit, just natural sugars along with fiber and important vitamins and minerals. Fruit digests more quickly than most other foods. When it’s eaten alone, it may be fully digested in under 30 minutes. When it’s eaten as part of a meal that contains protein and fat, however, then the entire meal is digested together and the rate of digestion depends on the amount of protein and fat in the meal.
Aim to keep fruit portions similar to the sizes listed in Appendix A . Generally that means a piece of fruit about the size of a tennis ball. For melons, berries, and mixed fruits, have up to one cup at a time. It’s okay to have fruit several times per day, but blood glucose is easier to control if you spread out the servings of fruit and eat just one portion at a time. It takes several servings of fruit to make a glass of juice, so skip the juice and eat the fruit instead. You don’t always need to pair fruit with fat, but it’s worth considering if you do want to slow digestion, which blunts the blood-glucose peak. If you have a little cheese or peanut butter with your apple, for example, then the apple is digested more slowly because fat delays digestion.
Focusing on complex carbs and fiber
Complex carbs and simple carbs are made out of the same building blocks, as you find out in Chapter 3 . Simple carbs such as fruit and sugar have only one or two sugar molecules, whereas complex carbs have many sugar molecules bound together. Starch and fiber are considered complex carbs:
· Starches: Starches can be broken down into individual sugar molecules during digestion. Those sugars are absorbed into the bloodstream.
· Fiber: Fiber is different. It can’t be digested. Dietary fiber continues through the intestine and is excreted in the stool.
It’s well known that fiber promotes intestinal health and reduces constipation, but did you know that fiber can lower blood-cholesterol levels? See Chapter 16 for details on soluble fiber and heart health.
Higher-fiber foods, such as whole grains, brown rice, oatmeal, and legumes, take longer to digest than refined white breads and white rice. Quick-digesting carb foods result in a steeper blood-glucose rise. White rice and brown rice, for example, both have the same amount of starch, but the brown rice has fiber, which slows digestion. Enzymes have to maneuver around the fiber to digest the starch. Consequently, glucose enters the bloodstream more slowly, and the blood-glucose rise is slightly blunted. Take note of your blood-glucose levels after eating refined versus whole grains to see how much of a difference fiber makes for you.
Take a look at Figure 10-1 . The two curves illustrate the rise and fall of blood-glucose levels after eating refined grains, as shown in curve A, versus whole grains, as shown in curve B. Notice the refined grains have a steeper blood-glucose rise and are finished digesting sooner than the whole grains. Choosing whole grains instead of refined grains may be one tool for reducing blood-glucose spikes after eating. Slower-digesting foods may also help you feel satisfied for longer and reduce the urge for snacking, which can help with weight-control efforts.
© John Wiley & Sons, Inc.
FIGURE 10-1: Blood-glucose response of refined versus whole grains.
Recognizing the fat factor
A balanced meal, which includes carbohydrate, protein, and fat, takes roughly four hours to digest. If the meal is especially high in fat, it may take longer. Simply stated, fat delays gastric emptying. Fatty foods are processed in the stomach for a sustained period of time before entering the intestine for digestion. Protein foods can slow digestion too, but that may be from the fat naturally present in the protein food. For example, all meats contain fat — some much more than others. Cheese and nuts have protein but are especially high in fat. Significantly delayed digestion can contribute to blood-glucose issues, especially if you take insulin before your meals.
If you take pre-meal insulin, it’s important that your insulin and your meals are well-timed, as discussed in Chapter 6 . A high-fat meal digests slower, so the rise in blood glucose tends to be delayed. The insulin taken prior to the meal can actively lower blood-glucose levels before the fatty meal digests — a mismatch in timing that can lead to hypoglycemia during or shortly after eating. Later, if the insulin wears off before the food has finished digesting, the blood-glucose levels can end up too high and stay high for hours after you eat the meal. Digestion timing and insulin timing need to line up. I discuss strategies for dealing with this situation later in this chapter.
The focus of this chapter is to highlight variables that affect digestion and absorption rates. Besides delaying digestion, fat content also correlates with calories consumed, which in turn influences body weight. For guidance on fitting in favorite foods yet eating for overall health, see Chapter 13 .
Considering other variables
A few other things can influence digestion rates and alter blood-glucose results, at least somewhat:
· Particle size: Grains that are pulverized into a powder digest quicker than larger grain particles.
· Degree of processing and addition of sugars: I frequently hear complaints about blood-glucose spikes from people who have dry cereal and milk for breakfast. The issue is that many breakfast cereals are made from highly processed grains, so digestion is quick. Additionally, cereals often have added sugars. If you aren’t accustomed to checking your blood glucose after breakfast, you may not have noticed how you respond to different meals. To observe the effect, check your blood-glucose levels an hour or two after breakfast and see whether meal composition makes a difference.
· Level of cooking: How long a food is cooked may have some effect. Pasta cooked al dente takes longer to digest than pasta that is soft-cooked or overcooked.
· Degree of ripeness: Riper fruits may digest more quickly or have more readily available sugars than unripe fruits; for example, your blood-glucose response may not be the same for a greener banana versus a riper banana.
· Length and type of grain: When it comes to rice, blood-glucose results may differ depending on whether it’s short-, medium-, or long-grain. Not everyone responds the same way to the same foods. Pay attention and see whether you note any differences between basmati, jasmine, red, black, or any other kind of rice that you eat. Certainly the portion size eaten is one of the most significant factors.
Before you start splitting hairs over the potential differences among the many varieties of apples, or what part of the country the food was grown in, or the soil conditions … reel those thoughts back in and focus on the most influential factors. They may boil down to the portion size of carbohydrates consumed, the fiber content, the level of processing, whether the carb is solid or liquid, and the composition of the foods eaten at the same time as the carbs. The American Diabetes Association (ADA) has a commonsense suggestion: Replace refined carbohydrates and added sugars with whole grains, legumes, fruits, and vegetables.
Gauging the Glycemic Index and Glycemic Load
The glycemic index (GI) is a tool to measure how individual foods are expected to impact blood-glucose levels. A food is scored on a scale of 0 to 100 according to how much it raises blood-glucose levels as compared with blood-glucose levels after the consumption of 100 grams of glucose. GI tables separate foods into three categories: low (0–55), medium (56–69), and high (70–100). High GI foods tend to be digested and absorbed quickly and cause a steeper rise in blood glucose. Low GI foods are expected to digest slowly and produce a more gradual rise in glucose levels.
Foods are evaluated one at a time. To determine the GI of a food, 50 grams of digestible carbohydrate (total carbohydrate minus grams of fiber) are consumed on an empty stomach after an overnight fast. Blood glucose is checked every 15 to 30 minutes for the next two hours. Finger-stick blood samples are monitored. The blood-glucose responses of ten people are averaged to determine the GI of each food.
According to GI tables, apple juice has a low GI, yet it is commonly used to treat hypoglycemia. Carrots have a high GI, but most people can munch them without a significant rise in blood glucose. According to GI scoring, white rice can fall in the low, medium, or high GI range. It depends on the type of rice, how it’s cooked, and even whether it’s reheated after being previously cooked. Numerous GI tables and calculators can be found in print and online, yet there are many inconsistencies in the GI scores when you compare sources. It can get pretty confusing.
Here are a few more things to consider:
· Most people do not eat one single food at a time on an empty stomach. When foods are eaten in a mixed meal that contains carbohydrate, protein, and fat, the glycemic effect differs. Meals are blended and churned in the stomach, and foods are digested together, not as separate components. The glycemic index score doesn’t predict how blood glucose will respond when foods are consumed in a mixed meal.
· The 50 grams of carbohydrate used to derive the GI score don’t necessarily coincide with normal portion sizes. A slightly rounded cup of cooked rice provides 50 grams of carb, which is a fairly common portion size. However, it may take close to 6 or 7 cups of cooked carrots to reach 50 grams of digestible carb. Most people simply don’t eat that many carrots at one time. When a typical portion of carrots is consumed, such as a half cup, blood-glucose response is quite flat.
· GI scores are based on a relatively small sample size of people.
Because the portion sizes studied were not always consistent with usual intakes, an alternate system was developed. The glycemic load (GL) is based on the typical portion sizes consumed. Glycemic load ranks the blood-glucose effect of foods when eaten in normal portion sizes, not the arbitrary 50 grams of carbohydrate used in constructing the glycemic index tables. Glycemic load has more utility simply because it reflects usual portions. For example, watermelon has a high glycemic index but a low glycemic load as long as portion size is controlled.
The question remains: Should consumers be looking at GI or GL tables before writing out their shopping lists? There’s no solid consensus among healthcare professionals. If glycemic tables help you reach your blood-glucose targets, it can be argued that they work for you. Evidence is mixed when you review study results. The ADA’s 2016 Standards of Care note the complexity of the glycemic index concept. The ADA cites several studies related to GI, but the results are mixed and inconclusive. Some studies showed that use of lower glycemic load carbs improved A1C values by 0.2–0.5 percentage points. Other studies showed no appreciable effect. It may be that portion control and exercise make a more significant impact on diabetes control than using glycemic tables.
Reducing Blood-Glucose Fluctuations: Tips and Tricks
Have you identified any particular foods that wreak havoc with your blood-glucose control? If those foods happen to be foods that you’re very attached to, finding solutions that enable you to include those foods — at least once in a while and in small portions — is important. (There’s no magic here — unfortunately, there are some limits to what your body can tolerate when you have diabetes.) The strategies in the following sections may help you fit in a favorite food without significant consequences to blood-glucose control.
Food choices matter when you have diabetes. Table 10-1 highlights key dietary factors that influence blood-glucose results (see the earlier section “Comparing Digestion Speeds for Fluids and Foods ” for more information). If you consider these points when planning meals and snacks, you may find it easier to reach your blood-glucose targets.
TABLE 10-1 Dietary Variables Affecting Glycemia
|
Variable |
Consideration |
|
Portion size |
Excess carb intake can sabotage blood-glucose control efforts. The larger the portion, the larger the amount of glucose that enters the bloodstream. |
|
Form |
Liquids digest rapidly, so they have the potential to raise blood-glucose levels more sharply than a comparable amount of carb in a solid food. |
|
Processing |
White, refined breads and processed grains typically cause a sharper blood-glucose rise than the same amount of the whole-grain version. |
|
Meal composition |
Having a balanced meal with carb, protein, and fat is usually better tolerated than just eating carbohydrate by itself. |
|
Concentrated sugars |
Sugar, honey, and syrups have concentrated amounts of carb in small servings. It’s important to use caution when sweetening foods or having desserts. |
|
Glycemic variance |
Individual variation exists. You may notice that certain foods affect your blood glucose more than other foods. It may have to do with particle size, level of cooking, or simply the way your body handles that food. |
Controlling portion sizes of foods that pack a blood-glucose punch
Reaching into the box of chocolates and taking one piece of candy isn’t a make-or-break situation when it comes to blood-glucose control. One such candy may contain roughly 10 grams of carb and 80 calories. It just boils down to how much willpower you have. If the candy is too tempting, keeping a box of chocolates on your kitchen counter may not be a great idea. If you can muster the self-control to limit your intake, keeping mini treats on hand is feasible.
Fruit juice has the potential to raise blood-glucose levels sharply for several reasons: It’s liquid, it’s concentrated in simple sugars, and it has no protein or fat to slow down digestion. Very small servings may be tolerated, provided your blood-glucose levels are near the lower end of your target range. Large portions of juice are unforgiving even if you eat something with protein and fat at the same time. Tolerance is tough simply because juice is concentrated in carbs. Fruit juice may be used in moderation before or during exercise sessions to prevent hypoglycemia. Blood-glucose results depend on your starting blood-glucose levels, the intensity and duration of the exercise, what type of diabetes you have, and whether or not you use medications such as insulin.
Use Chapter 5 to set reasonable daily carbohydrate intake targets. Chapter 6 provides guidelines on how to best distribute the carbohydrate into manageable meals and snacks. As long as your diet is balanced and healthy for the most part, you can budget in occasional special treats. Account for the carbs by fitting them into your usual meal plan. That may mean eating a lower-carb meal when you plan to fit in a dessert with carbs. You can also counteract the effects of carbs somewhat by increasing your activity level, which is the focus of the next section.
Adding activity for extra carbs
If you end up slightly overdoing the carb budget, you may be able to offset the effects by adding exercise. A stationary bike or treadmill comes in handy when you need to add a quick exercise session. Weather permitting, a walk outside is another option for burning off the extra carbs and calories. However, you may need to walk or cycle for 20 to 30 minutes just to burn off 100 calories, so think twice before reaching for that pastry with 500 calories. Check out Chapter 14 for more about fitness.
Combining foods to reduce glycemic effect
Digestion rates are affected by how foods are combined. For example, white rice and white bread are refined and low in fiber, so they tend to bump up blood-glucose levels more sharply than whole grains. Putting peanut butter or almond butter on the white bread slows down the digestion and absorption of the bread, which may blunt the blood-glucose rise. Likewise, serving rice with stir-fried vegetables and fish, beef, chicken, pork, or tofu may reduce the glycemic effect of the rice. Of course, you still need to control the portion size of the rice! Plan balanced meals using the simple plate model as discussed in Chapter 8 , or view sample meal plans and snack ideas in Part 5 .
Altering the order in which you eat the components of your meal
Sometimes blood-glucose levels are higher than desired when you’re about to sit down to have a meal. If you typically take insulin to cover your carbs, it may not hurt to give the insulin a head start when you’re hyperglycemic at mealtime. After injecting the insulin, you can opt to start with the low-carb or carb-free foods first. Begin with salad, and then work your way through most of the protein and vegetables. Doing so allows the insulin a chance to chisel down the blood-glucose levels somewhat before you munch on carbs.
If you’re battling to get blood-glucose levels into a reasonable range, don’t try to fit in sweets and treats. Don’t overdo the carb portions when your blood-glucose levels are up. Sometimes it takes a few lower-carb meals to get blood-glucose levels back into the target zone. If your blood glucose remains elevated despite diet modification efforts, you may need medication dosage adjustments. Ask your healthcare provider for advice on meds.
Aligning Insulin and Digestion Rates
It’s important to follow your doctor’s recommendations and take insulin as prescribed. However, having a firm understanding of how your insulin works is very helpful. Numerous kinds of insulin are available to treat diabetes, and they differ. Some types of insulin are designed to cover the carbs in the meal, while others have profiles that are meant to match the glucose that is being released from your liver between meals and while you sleep. Chapter 6 describes the onset, peak, and duration times for the various insulins. When, specifically, does the insulin start to work? How long does it take for the insulin to reach its peak (strongest) effect? And how long does the insulin continue to work before it wears off? “Insulin insight” is a powerful tool that you can use to problem-solve and improve diabetes management.
Mealtime insulin must be aligned with digestion timing. If insulin gets into the bloodstream before the carbs digest, blood-glucose levels can drop. If the carbs digest quickly and enter the bloodstream before the insulin is working, blood-glucose levels can spike. I’m tempted to repeat the cliché that “timing is everything,” but there are too many important variables to say that, so I’ll settle for timing matters.
This chapter focuses on factors that affect how long it takes for foods to digest: liquids being faster than solids, refined grains digesting quicker than whole grains, and fat slowing down digestion by delaying gastric emptying. When a meal contains carbohydrates, proteins, and fats in reasonable amounts, the meal takes about four hours to digest. The highest blood-glucose level is about one to two hours after eating the meal. Rapid-acting insulin tends to be a good fit for most meals because it works its hardest an hour after being injected and wears off in about four hours. But some meals take longer to digest, especially meals that are high in fat, are fried, or have significant amounts of meat or cheese. When high-fat meals digest slowly, the timing of rapid-acting insulin may no longer match the digestion timing of the meal.
Understanding insulin action times as well as how long it takes for foods to digest allows you to make decisions about how to best align the two, as described in the upcoming sections.
Optimizing mealtime insulin coverage
Blood glucose is expected to be at its highest level about one to two hours after a meal, as long as it is a fairly balanced meal and not excessively high in fat. The meal should be finished digesting in roughly four hours. Rapid-acting insulin works its hardest (peaks) about an hour after being injected and finishes working in about four hours. See Figure 10-2 . The dotted line represents the onset, peak, and duration of rapid-acting insulin. The shaded curve represents the blood-glucose levels rising and resolving after eating. As illustrated, the insulin action and the digestion and absorption of glucose from the meal line up nicely.
© John Wiley & Sons, Inc.
FIGURE 10-2: Rapid-acting insulin and a balanced meal.
Recall that fatty meals digest slower. Figure 10-3 illustrates what may happen when rapid-acting insulin is taken before a meal that has a significant amount of fat. Again, the dotted line represents the timing of the insulin and the shaded curve represents the blood-glucose levels resulting from a high-fat meal. It may be a meal composed of fried foods, large portions of fatty meat, a cheesy meal, or a meal with a lot of added fats: butter, mayo, sour cream, salad dressing, or guacamole. The rapid-acting insulin works at its normal rate, but the fatty meal digests slower than a normal meal. Consequently, the insulin may peak before the meal digests, which could cause hypoglycemia during the meal. Later, when the food finally digests, the insulin has passed its peak and doesn’t have enough strength to lower the blood glucose, so glucose levels remain elevated. Such a situation can lead to high blood-glucose levels at bedtime after eating a high-fat dinner.
© John Wiley & Sons, Inc.
FIGURE 10-3: Rapid-acting insulin and a fatty meal.
One solution may be to take the insulin midway through the meal or toward the end of the meal. Giving a fatty meal a head start can improve the way the insulin and the blood-glucose timings align.
Discuss adjustments to injection timing with your healthcare provider prior to making changes to your regimen.
Using your insulin pump’s fine features
An insulin pump has a feature that comes in handy when trying to match insulin action to slowly digesting fatty meals. If you aren’t familiar with an insulin pump, a quick overview is needed. An insulin pump is a small, battery-driven, computerized device that delivers insulin. The pump contains only one type of insulin: rapid-acting. The pump has two main modes of insulin delivery: basal and bolus.
· Basal delivery: The basal rate delivers tiny doses of insulin continuously. It’s like a steady drizzle. Basal insulin delivery replaces the need for long-acting insulin. The basal rate matches the glucose that is being released from the liver.
· Bolus delivery: This type of delivery comes into play when the user directs the pump to release a dose of insulin to cover the carbs in a meal. You can also bolus a correction dose of insulin if blood-glucose levels are above target.
A doctor who specializes in diabetes helps determine appropriate basal rates and bolus ratios.
An insulin pump can release a programmed insulin dose that more closely matches a slow digesting fatty meal. See the dotted line in Figure 10-4 , which illustrates insulin action in a “combo bolus,” also known as a “dual wave.” The user can direct the pump to deliver part of the insulin dose before the meal and part of the dose in small bursts over one or more hours.
© John Wiley & Sons, Inc.
FIGURE 10-4: Insulin pump combo-bolus with a fatty meal.
For example, say a person determines her insulin dose for pizza will be 6 units. She can opt to take 3 units up front and 3 units delayed. She can choose to have the delayed portion delivered incrementally over two or three hours, or whatever works for her. She can monitor results by observing her blood-glucose results. If she’s not fully satisfied with the results, she can tweak her formula the next time. She might try 2 units up front and 4 units delayed. She can try any number of things. It does take some trial and error to see what works best for pizza versus what works best for a cheeseburger and fries. Diabetes educators and pump trainers can provide tips and guidance.