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ОглавлениеChapter 5 Nutrition Therapy for Adults with Type 1 and Insulin-Requiring Type 2 Diabetes
Alison B. Evert, MS, RD, CDE
Nutrition Therapy for Type 1 Diabetes and Insulin-Requiring Type 2 Diabetes
Highlights Nutrition Therapy for Adults with Type 1 and Insulin-Requiring Type 2 Diabetes
• Carbohydrate intake and available insulin are the primary determinants of postprandial glucose levels. Management of carbohydrate intake is therefore a primary strategy for achieving glycemic control.
• Adjusting prandial insulin doses to match desired carbohydrate intake (using a meal-planning approach such as carbohydrate counting) in people with type 1 diabetes results in improved glycemic control.
• For individuals using fixed daily insulin doses, carbohydrate intake on a day-to-day basis should be kept consistent with respect to time and amount.
• Prandial and blood glucose correction insulin-dosing algorithms may help people with type 1 and insulin-requiring type 2 diabetes to achieve glycemic control when using flexible intensive insulin therapy.
• Timing of prandial insulin dose 15–20 min before initiation of the meal may help to reduce postprandial hyperglycemia.
• Postprandial hyperglycemia and glucose variability occur frequently in people with diabetes, and this result may convey increased risk of cardiovascular morbidity and mortality. Nutrition therapy interventions may help to reduce postprandial hyperglycemia and reduce glycemic variability.
Nutrition Therapy for Adults with Type 1 and Insulin-Requiring Type 2 Diabetes
Nutrition therapy plays an integral role in the treatment and self-management of type 1 diabetes and insulin-requiring type 2 diabetes. The Centers for Disease Control and Prevention (CDC) estimates that 25.8 million people are affected by diabetes. Out of these people, 12% of adults with diagnosed diabetes (type 1 or type 2) are treated with insulin and an additional 14% take insulin and oral medication(s) (CDC 2011).
For centuries, the only therapeutic option for type 1 diabetes was “starvation diets”; thankfully, this strategy was ultimately short-lived. After 1922, insulin became available and, in the 1980s, the technology for self-monitoring blood glucose (SMBG). However, despite all the advances in the treatment of insulin-requiring diabetes, nutrition therapy continues to be a difficult strategy for individuals to implement. For the individual with type 1 (or type 2) diabetes, learning how to administer an injection of insulin is a skill that is often quickly mastered, whereas mastering the ability to “count carbohydrates” and match insulin to food intake is usually more difficult.
There are two types of normal physiological insulin secretion: continuous basal insulin secretion and incremental prandial insulin secretion, controlling meal-related glucose excursions. People with type 1 and insulin-requiring type 2 diabetes lack both basal and meal-related prandial secretion. Historically, conventional treatment included predetermined or “fixed” insulin doses and following a rigid calorie- and carbohydrate-controlled meal plan based on the insulin regimen. Some people with type 1 and insulin-requiring diabetes still use this method for a variety of reasons, such as age, cost, fewer required injections, lack of access to insulin analogs, personal preference, or prescribing habits of the health care provider.
In the 1990s, the Diabetes Control and Complications Trial (DCCT) showed unequivocally that intensive insulin therapy using multiple daily injections reduced the risk of complications when compared to conventional treatment (DCCT 1993). Improved glycemic control was achieved through an intensive program of multiple daily insulin injections (at least three injections per day) or the use of an insulin pump. Intensive insulin therapy DCCT participants performed SMBG (four times per day) and were taught how to adjust their insulin using treatment algorithms based on glucose test results, food choices, and physical activity. Carbohydrate counting was used as one of the meal-planning approaches and was found to be effective in helping people achieve glycemic control (DCCT 1993).
Outside of the United States, flexible intensive insulin therapy (FIIT) for the management of type 1 diabetes was developed in Düsseldorf in the late 1970s (Mühlhauser 1983). FIIT is now taught as a part of many structured education programs, such as the Dose Adjustment for Normal Eating (DAFNE) course in the United Kingdom and in Australia (DAFNE 2002; Lowe 2008).
Both the DCCT and DAFNE research trials involved frequent follow-up with members of the diabetes team that included registered dietitians (RDs) and nurses to assist the person with diabetes on an ongoing basis to adjust insulin doses (DCCT 1993; DAFNE 2002). The improvements in blood glucose were the result of physiological insulin replacement combined with self-management of insulin dose adjustment in conjunction with a “flexible” meal-planning approach such as carbohydrate counting. Excellent reviews are available to guide insulin initiation and management of insulin therapy to achieve optimal glycemic control; therefore, this topic will not be extensively reviewed here (DeWitt 2003; Mooradian 2006).
The chapter begins with a review of the literature pertaining to insulin dose algorithms, especially as they relate to insulin-to-carbohydrate ratios, timing of prandial insulin doses, and factors contributing to postprandial hyperglycemia. Nutrition therapy using carbohydrate-counting meal-planning approaches is reviewed and incorporates research published after 1 September 2009.
Insulin-Dosing Algorithms
Since the advent of basal-bolus insulin therapy and SMBG, there has been interest in developing insulin-dosing algorithms for the self-adjustment of insulin therapy, and a variety of formulas or “rules” have been developed (Skyler 1981; Palerm 2007). Prandial dosing algorithms are commonly referred to as an insulin-to-carbohydrate ratio (ICR), and blood glucose correction algorithms are frequently referred as an insulin sensitivity factor (ISF). Guidelines also exist for estimating basal insulin as a fraction of the total daily dose (TDD) (see Table 5.1 for definitions of basal-bolus insulin terms).
Table 5.1 Basal-Bolus Insulin Therapy Terms
• Physiological insulin replacement: The insulin secretion of normally functioning b-cells is mimicked with prandial (mealtime) or “bolus” insulin and long-acting or “basal” insulin.
• Basal insulin: Basal insulin represents the level of insulin always present in fasting and postmeal states. Basal insulin suppresses excess gluconeogenesis and the release of free fatty acids and enables the glucose transport in the fasting state. Insulin glargine and detemir are examples of “basal” insulin and are essentially peakless. Neutral protamine Hagedorn (NPH) can also be used as a basal insulin, but it has a pronounced peak. Basal insulin delivery can also be delivered via an insulin pump using either rapid- or short-acting insulin (see examples listed under “Bolus insulin” below). Basal insulin typically represents ~50% of the TDD insulin required each day.
• Bolus insulin: Rapid-acting insulin (lispro, aspart, and glulisine) or short-acting insulin (regular) can be used at mealtimes and/or to correct an elevated blood glucose level. In the case of rapid-acting insulin, onset is typically 5–15 min and peak action is at 30–90 min after injection. The duration of rapid-acting insulin is ~4–6 h in most people. This is the “other” 50% of the TDD insulin required each day.
• Total daily dose (TDD): TDD is the total number of units taken each day to achieve desirable blood glucose control. This number includes basal insulin plus bolus insulin used to “cover” the carbohydrates consumed at meals and the blood glucose correction needs.
PRANDIAL INSULIN: • ICR or carbohydrate factor (CarbF): This ratio indicates how many grams of carbohydrate are “covered” or “matched” by 1 unit rapid- or short-acting insulin. The ICR is related to an individual’s insulin sensitivity and body size. An ICR for an adult with type 1 diabetes is typically 1:10 (1 unit of rapid-acting insulin is needed to “match” 10 g carbohydrate), whereas an obese person might require an ICR of 1:5 (1 unit of rapid-acting insulin to “match” 5 g carbohydrate due to insulin resistance).
GLUCOSE CORRECTION INSULIN: • ISF or glucose correction factor (CorrF or CF): The ISF can be defined as the estimated drop in blood glucose (mg/dL) expected from the administration of 1 unit of rapid- or short-acting insulin. ISF is also related to the individual’s insulin sensitivity and body size. A typical ISF for an adult with type 1 diabetes is typically 1:50 mg/dL (1 unit of rapid-acting insulin will drop the blood glucose level 50 mg/dL). However, an overweight/insulin-resistant person may have an ISF of 1:20 mg/dL (1 unit rapid-acting insulin will drop the blood glucose level 20 mg/dL).
The “1500 rule” for blood glucose correction was an original formula based on informal clinical observations using regular insulin by Davidson and his colleagues in 1982 (Table 5.2) (Davidson 2008). In 1998, Davidson and colleagues developed a formula for the ICR, and in 2008, they published a paper on how their mathematical models for basal-bolus insulin-dosing guidelines in patients with type 1 diabetes were derived from a retrospective controlled study (Davidson 2008). The goal of their analysis was to determine how best to prescribe insulin for use in continuous subcutaneous insulin infusion (CSII) pump therapy in their large endocrine practice. These formulae were statistically correlated and are referred to as the Accurate Insulin Management (AIM) formulae (Davidson 2002; Davidson 2003). The AIM system guidelines are based on the TDD. If the TDD is not available, the AIM system includes an additional formula to estimate TDD based on body weight in pounds (Table 5.2).
Table 5.2 Insulin Dosing Formula or “Rules”
In 1990, Howorka and colleagues also developed prandial algorithms (meal-related and correctional insulin doses for blood glucose increases induced by carbohydrate) for personalized adjustment with flexible insulin dosing (Table 5.3) (Howorka 1990). These formulae are still used by some researchers outside the U.S. In an observational study of 35 patients with type 1 diabetes using the Howorka flexible intensive insulin therapy algorithms, the authors concluded that use of these individualized parameters permitted fast and accurate adjustment of insulin doses (Franc 2009). Howorka also proposed additional algorithms for protein/fat in meals low in carbohydrate. However, the protein/fat algorithms have not been extensively studied, and patients are not being taught to use these currently in clinical practice. Another researcher proposed the addition of 1 unit of insulin per 20 g protein (Sachon 2003).
Table 5.3 Howorka Algorithms for Flexible Insulin Therapy
Other researchers also determined ICR through use of the hyperinsulinemic-euglycemic clamp with a meal challenge to determine a prandial dosing algorithm in people with type 1 diabetes (Bevier 2007). In 1994, based on clinical experience, a carbohydrate factor formula was introduced: a “450 rule” for multiple daily injection and CSII patients (Walsh 1994). An updated carbohydrate factor formula and a glucose correction factor formula were published in the consumer book Using Insulin (Table 5.2) (Walsh 2003). The authors have further refined their formula after analyzing anonymous consecutive downloads from 1,020 pumps collected during a routine pump software upgrade in 2007 (Walsh 2010).
It should be noted that a majority of these popular ICR and ISF formulae were derived from patient populations using CSII with well-controlled blood glucose levels, not multiple daily injections. The authors of the AIM system recommend use of their formula for patients with type 1 diabetes, noting that only one person with insulin-requiring type 2 diabetes was included in their data analysis (Davidson 2008).
Timing of Prandial Insulin Dose
DeWitt and Hirsch described the term “lag time” in their reviews of outpatient insulin therapy in type 1 and type 2 diabetes (Hirsch 2005a; DeWitt 2003). Lag time is defined as the amount of time that elapses between the prandial insulin injection and a meal; lag time is critical in the control of postprandial hyperglycemia and in later risk of hypoglycemia. Given the pharmacodynamics of insulin analogs, sufficient lag time helps to decrease postprandial hyperglycemia (Rassam 1999). The use of lag time for rapid-acting insulin and improved matching action with carbohydrate absorption explains their clinical advantage (DeWitt 2003). In the pre-analog era, it was recommended to administer regular insulin ~20–30 min before eating a meal. With the introduction of rapid-acting insulin analogs, many physicians recommended injection of the prandial dose just before eating, or even after eating. However, these recommendations are not supported by the insulin action times reported by the insulin manufacturers (Hirsch 2005a). The insulin action times of the currently available rapid-acting insulin analogs are as follows: onset 5–15 min, a peak between 30 to 90 min, and duration of ~4–6 h.
A study designed to determine the most effective timing of rapid-acting insulin analog (Novorapid®) with CSII in children with type 1 diabetes reported that glucose levels 3 h after the meal were lower when the prandial insulin was administered 15 min or immediately before the meal, rather than after the meal (Scaramuzza 2010). Also demonstrated was a significant difference in 1-h postprandial glucose levels, which were significantly higher when the prandial insulin was given after the meal and lowest when the insulin was administered 15 min before the meal. This result occurred even if the blood glucose was in the hypoglycemic range before eating.
Subjects with type 1 diabetes using CSII participated in a crossover study consisting of three treatment arms: delivering rapid-acting insulin analog (glulisine) 20 min before a meal, immediately before the meal, and 20 min after the meal initiation (Cobry 2010). At both 60 and 120 min after meal initiation, the 20-min before-meal insulin arm showed significantly lower glycemic excursions than when the prandial insulin was given immediately before the meal. Glycemic area under the curve was significantly less in the before-meal insulin group than in both the immediately before- or after-meal initiation groups. The authors concluded that although delivering the prandial dose of insulin 20 min before the meal may be inconvenient, it is an important strategy that can result in a reduction of postprandial glucose levels over 180 mg/dL.
Another trial assessed the effect of the rapid-acting insulin analog (aspart) timing on postprandial glucose levels in subjects with type 1 diabetes using CSII when the prandial insulin was administered at 30, 15, or 0 min before mealtime (Luijf 2010). The administration of the prandial insulin 15 min before mealtime resulted in lower postprandial glucose excursions and more time spent in desirable ranges without an increase in hypoglycemia.
Data from these three small studies argue for administration of rapid-acting insulin analogs 15–20 min before the start of the meal. However, larger trials outside the clinical research center are needed to confirm these findings. Tridgell and colleagues proposed progressively longer lag times for rapid-acting prandial and correction dose insulin depending on the degree of hyperglycemia (Tridgell 2010) (see Table 5.4 for lag times for prandial insulin).
Table 5.4 Recommended Insulin Lag Times for Rapid-Acting Insulin Based on Degree of Preprandial Hyperglycemia
When recommending preprandial times, clinical judgment is required in specific patient populations such as young children or the elderly, who do not have predictable food intake (Tridgell 2010). It may be appropriate to give these individuals the dose of prandial insulin during the meal or immediately after the meal to reduce the risk of hypoglycemia. In addition, individuals with delayed gastric emptying may benefit from administration of rapid-acting insulin at the end of the meal or the use of regular insulin 30 min before the start of the meal (see Chapter 18, Nutrition Therapy for Diabetic Gastropathy).
If hypoglycemia is determined before the start of a meal, the individual should treat the low glucose level with a carbohydrate food, inject the prandial insulin, and then eat (Scaramuzza 2010). Others have suggested treating the hypoglycemia and delaying the prandial injection for a brief time (Trigdell 2010). On the basis of clinical experience, the individual could additionally be advised to reduce the prandial insulin dose or instructed to increase carbohydrate food consumed at the meal.
Postprandial Glycemic Control and Diabetes Complications
Diabetes management decisions have traditionally been made using fasting and premeal blood glucose measurements as well as A1C test results. This approach has left many people with diabetes with suboptimal glycemic control because of inadequate control of postprandial hyperglycemia. Postprandial glucose excursions and postprandial hyperglycemia occur frequently in people with diabetes, even when A1C may be <7%, and this result may convey increased risk of cardiovascular morbidity and mortality (Ceriello 2005; Home 2005). Advocates of postprandial monitoring propose that it is critical to the establishment of good glycemic control (Hirsch 2005b; Tridgell 2010), whereas others are not convinced that postprandial SMBG is essential (Buse 2003).
Some surrogate measures of vascular pathology, such as endothelial dysfunction, are negatively affected by postprandial hyperglycemia (American Diabetes Association [ADA] 2012; Ceriello 2002). The mechanisms through which postprandial hyperglycemia exerts its effects may be related to the production of free radicals, which in turn can induce endothelial dysfunction and inflammation (Ceriello 2006).
It has been proposed that dysglycemia of patients with diabetes is the sum of the two following disorders: 1) sustained chronic elevations of glucose and 2) glycemic variability with its main component of postprandial excursions (Monnier 2003). Glucose variability not only includes upward acute fluctuations (postprandial excursions), but also includes downward changes (i.e., decreases from either baseline or interprandial concentrations to glucose nadirs) and is also associated with activation of oxidative stress, one of the main mechanisms leading to diabetes complications (Brownlee 2006). It is therefore suggested that both glycemic variability and postprandial excursions should be monitored and managed in people with diabetes.
In addition, in people with type 2 diabetes, it was reported that there is a progressive shift in the respective contributions of fasting and postprandial hyperglycemia when patients progress from moderate to high hyperglycemia, with the contribution of postprandial glucose excursions being predominant in patients with moderate diabetes. In addition, the contribution of fasting hyperglycemia increases with worsening diabetes (Monnier 2003). The results of the Monnier study suggest that as the patient gets closer to A1C goals of 7%, more attention must be given to reducing postprandial hyperglycemia. Therefore, effective management of diabetes must also include control of postprandial glucose levels, with current guidelines recommending postprandial blood glucose levels <180 mg/dL (ADA 2012).
Other Diabetes Medications for Treating Postprandial Hyperglycemia
People with type 2 as well as type 1 diabetes may have significant postprandial hyperglycemia because of a rapid influx of glucose from the gut (resulting from increased gastric motility), impaired insulin release, excess hepatic glucose production (from inappropriate elevations in glucagon), and insulin resistance (Sudhir 2002). Nine distinct classes of medications are now available for treatment of diabetes in the U.S. and six specifically affect postprandial hyperglycemia: meglitinides, a-glucosidase inhibitors, incretin mimetics, an amylin analog, dipeptidyl peptidase-4 inhibitors, and insulin. Two of these classes of medications, the incretin mimetics (exenatide and liraglutide) and the amylin analog (pramlintide), in addition to their ability to treat these numerous abnormalities, are also associated with modest weight loss (Garber 2011; Nathan 2009).
NUTRITION THERAPY FOR TYPE 1 DIABETES AND INSULIN-REQUIRING TYPE 2 DIABETES
The ADA published nutrition recommendations and interventions in 2008 (ADA 2008). These recommendations are integrated into their annual standards of medical care and updated as new evidence becomes available (ADA 2012). In addition, in 2008, the Academy of Nutrition and Dietetics (formerly the American Dietetic Association) (Acad Nutr Diet) published evidence-based nutrition practice guidelines (EBNPG) for adults with type 1 and type 2 diabetes in the Acad Nut Diet Evidence Analysis Library (EAL) (Acad Nutr Diet 2008). Subsequently, a review of the research leading to the EBNPG and a summary of the research published after the completion of the EAL (through 1 September 2009) were published (Franz 2010).
To update this chapter, a literature search was conducted using PubMed MEDLINE for research published after 2009 on nutrition therapy for insulin-requiring adult patients. Search criteria included the following: carbohydrate counting, medical nutrition therapy, dietary therapy, healthy eating, nutrition counseling, nutrition education, glycemic index, glycemic load or treatment research in human subjects with type 1 diabetes, and English language articles. Study design preferences were randomized controlled trials, clinical controlled studies, large nonrandomized observational studies, cohort studies, or case-controlled studies. The literature search identified 251 articles. Fifteen articles were retrieved for more detailed evaluation, and two articles were identified from reference lists. Of these, 10 met inclusion criteria and are included in Table 5.5.
Table 5.5 Studies on Nutrition Therapy for Adults with Type 1 Diabetes: Carbohydrate-Counting Meal-Planning Approach
Nutrition Therapy Interventions
Based on the results of the DCCT, ADA recommends intensive insulin therapy for type 1 diabetes, using basal and bolus insulin to reproduce or mimic normal physiological insulin secretion: 1) use of multiple-dose insulin injections (three to four injections per day of basal and prandial insulin) or insulin pump therapy; 2) matching prandial insulin-to-carbohydrate intake, premeal blood glucose, and anticipated activity; and 3) for many people (especially if hypoglycemia is a problem), use of insulin analogs (ADA 2012). The use of basal and prandial insulin replaces insulin in a way that closely approximates normal physiological patterns.
Insulin therapy should be integrated into the individual’s usual eating and physical activity pattern; individuals using rapid-acting insulin by injection or insulin pump should adjust the meal and snack insulin doses on the basis of carbohydrate content of the meals and snacks. In individuals using fixed daily doses, carbohydrate intake on a day-to-day basis should be kept consistent with respect to time and amount. For planned exercise, insulin doses can be adjusted; for unplanned exercise, extra carbohydrate may be needed (ADA 2008).
Achieving nutrition-related goals requires a coordinated team effort that includes the person with diabetes and involves the patient in the decision-making process. Because of the complexity of nutrition issues, it is recommended that an RD who is knowledgeable and skilled in implementing nutrition therapy into diabetes management and education be the team member who plays the leading role in providing nutrition therapy (ADA 2012). However, all team members, including physicians and nurses, should be knowledgeable about nutrition therapy and support its implementation (ADA 2008).
The Acad Nutr Diet EBNPG state the following: “Medical nutrition therapy (MNT) plays a crucial role in managing diabetes and reducing the potential complications related to poor glycemic, lipid, and blood pressure control” (Franz 2010; Acad Nutr Diet 2008). Carbohydrate intake and available insulin are the primary determinants of postprandial glucose levels. Therefore, management of carbohydrate intake is the primary strategy for achieving glycemic control. For individuals who adjust mealtime (prandial) insulin or who are on CSII, insulin doses should be adjusted to match carbohydrate intake (ICRs). Comprehensive nutrition education and counseling should be provided that includes instruction on interpretation of blood glucose monitoring patterns and nutrition-related medication management. Specifically, people using “flexible” insulin dosing to manage their diabetes need to understand the relationship and coordination of their basal-bolus insulin plan (insulin action) with the blood glucose–raising effect of their carbohydrate intake.
In people with type 1 (or type 2) diabetes using “fixed” insulin doses, meal and snack carbohydrate intake should be consistently distributed throughout the day on a daily basis, since consistency in carbohydrate has been shown to result in improved glycemic control (Acad Nutr Diet 2008). It is recommended that individuals using “fixed” daily doses of insulin use a carbohydrate-counting meal-planning approach or some other method of quantifying carbohydrate intake to maintain day-to-day consistency, both in the timing and quantity of food intake.
Food Factors Affecting Glycemic Control
There is more to controlling postprandial hyperglycemia than knowing how to “count carbohydrates.” Many people with type 1 (and type 2) diabetes struggle to comprehend how their blood glucose levels can dramatically fluctuate on a daily basis despite eating the same number of grams of carbohydrate at meals.
One reason may be a lack of adequate education on how to accurately dose prandial insulin and quantify carbohydrate intake (Boukhors 2003). The CDC reports that only 55.7% of people with diabetes participate in a diabetes self-management education class, suggesting that many people with type 1 (and type 2) are never formally instructed on a meal-planning approach, such as carbohydrate counting, to enable them to accurately quantify their carbohydrate intake (CDC 2011). Consequently, these individuals may either underdose or overdose prandial insulin requirements. Accurate dosing of prandial insulin to actual food (grams of carbohydrate) intake is a key component of basal-bolus insulin therapy.
Another reason may be that in addition to determining the number of grams of carbohydrate consumed at meals, several extrinsic and intrinsic variables may influence the impact of carbohydrates on the postprandial response (ADA 2008). Extrinsic variables that may influence glucose response include macronutrient distribution of the meal, fasting or preprandial blood glucose level, available insulin, antecedent exercise, and degree of insulin resistance.
Intrinsic variables that influence the effect of the carbohydrate-containing foods on blood glucose response include type and source of carbohydrate, the physical form of the food (e.g., whole food versus juice), type of starch (e.g., amylopectin versus amylose), method of food preparation (e.g., baking versus frying), cooking time and amount of heat and moisture used, degree of processing, and ripeness of food (ADA 2008). Individuals can use information from SMBG and continuous glucose sensors to learn how specific foods affect their glycemic control.
Meal-Planning Approaches and Tools
Type 1 diabetes. Meal-planning approaches other than carbohydrate counting, such as the glycemic index, also have been studied. A food insulin index, a physiological basis for ranking foods according to insulin “demand,” was developed by a group of researchers in Australia for 120 single foods (Bao 2009). They concluded that the relative insulin demand evoked by mixed meals consumed by lean healthy subjects is best predicted by a physiological index (food insulin index) based on integrating insulin responses to isoenergetic portions of single foods and that eating patterns that provoke less insulin secretion may be helpful in preventing and managing diabetes. In 2011, Bao compared a novel algorithm based on the food insulin index for estimating mealtime insulin dose with carbohydrate counting in adults with type 1 diabetes using CSII (Bao 2011). They concluded that when compared with carbohydrate counting, the food insulin index algorithm improved acute postprandial glycemia in well-controlled subjects with type 1 diabetes. The authors acknowledge that implementation of these findings outside the laboratory setting is not practical at this time, since the food insulin index does not currently appear on food labels and the food insulin index database includes only ~120 foods.
Another group collected data on food intake, physical activity, insulin administration, and blood glucose test results in patients with type 1 diabetes using self-administered questionnaires (Ahola 2010). A total of 64% of the participants inappropriately estimated their prandial insulin, and the authors concluded that optimal prandial insulin dosing is not easy, even after a long duration of diabetes.
Insulin dosing aids such as bolus insulin calculation cards and dosing guides have been developed to assist people with diabetes in reducing potential calculation errors (Anderson 2009; Chiarelli 1990; Kaufman 1999). Bolus calculators with personalized insulin-dosing algorithms can be programmed for use in a wide range of devices, such as personal digital assistants (PDAs), Smartphone applications, or insulin pumps (Gross 2003; Błazik 2010).
The use of a Diabetes Interactive Diary, an automatic carbohydrate/insulin bolus calculator installed on a mobile phone, also using patient-physician communication via text messages, was compared with a standard carbohydrate-counting education program (Rossi 2010). The Diabetes Interactive Diary was as effective as a traditional carbohydrate-counting education program, without an increased risk of hypoglycemia. The authors concluded that use of this type of technology reduces education time while significantly improving treatment satisfaction and several quality-of-life dimensions. These types of adaptive aids are popular with the tech-savvy, but can also be useful for people who have health literacy and numeracy concerns, such as young children or adults who do not possess the ability to perform fairly complex mathematical equations required in intensive insulin therapy plans (Wolff 2009). Use of technology may allow more people with insulin-requiring diabetes to have access to diabetes self-management tools, education, and support.
Type 2 diabetes. Most people with type 2 diabetes will eventually need insulin to achieve target A1C values (Wright 2002). The U.K. Prospective Diabetes Study (UKPDS) showed that b-cell failure is progressive; there is 50% normal b-cell function at diagnosis, with a steady decline after diagnosis (DeWitt 2003; UKPDS 1998). It is also reported that 53% of people with type 2 diabetes initially treated with sulfonylureas require insulin therapy by 6 years, and almost 80% require insulin by 9 years (Turner 1999; Wright 2002).
A small clinical trial examined metabolic control and patient preference in people with type 2 diabetes using conventional “fixed” or flexible insulin therapy (Kloos 2007). The authors concluded that initiation of insulin therapy was safe and effective in both treatment options, but after initially improving glycemic control, neither group achieved A1C levels <7%. After 8 weeks of following both the fixed and flexible insulin plans, the participants stated that they preferred the last therapy they received.
The first randomized study to evaluate intensive basal-bolus analog insulin therapy in people with type 2 diabetes as well as efficacy of carbohydrate counting in this population was conducted in 2008 (Bergenstal 2008). The simple algorithm group was provided with a set dose of prandial insulin to take before meals and compared to a group instructed on carbohydrate counting by an RD who provided an ICR to use for each meal. Prandial and basal insulin levels were adjusted weekly in both groups on the basis of SMBG results from the previous week. A1C levels at the end of study were 6.7% (simple algorithm) and 6.54% (carbohydrate counting). The respective mean A1C changes from baseline to 24 weeks were –1.46 and –1.59% (P = 0.24). Both groups used SMBG results to dose insulin. The simple algorithm group participants either consumed fairly consistent amounts of carbohydrates, thus minimizing needed changes in insulin dosing, or learned to modify their carbohydrate intake on the basis of SMBG results.
Factors That May Affect Long-Term Adherence to Basal-Bolus Insulin Regimens
Three studies exploring the food and eating practices of people with type 1 diabetes converted to FIIT as part of the DAFNE course have been published (Lawton 2011; Rankin 2011; Casey 2011). One study reported that adoption of this type of insulin treatment plan can result in greater dietary rigidity over time as opportunities presented for greater dietary freedom are counterbalanced by new challenges and burdens (Lawton 2011). For example, in an effort to simplify food choices for easier carbohydrate estimation, the individual may rely on prepackaged foods that include nutrition fact information rather than on naturally occurring, unprocessed foods such as fresh fruits and vegetables that do not have food labels. This step could lead to increased consumption of saturated fats and salt. FIIT participants also articulated anxieties about miscalculating carbohydrate amounts and injecting the wrong dose, resulting in the tendency to eat the same things over and over again, limiting intake of new foods or foods with difficult-to-determine carbohydrate content. Some participants purposefully choose low-/no-carbohydrate foods to safely simplify calculations of prandial doses. Despite participation in formal intensive insulin therapy classes, fear of hypoglycemia when matching mealtime insulin to desired food (carbohydrate) intake continues to be a concern for many (Lawton 2011).
Another investigation over 12 months explored participant experiences regarding how they sustain use of FIIT (Rankin 2011). Although patients generally preferred flexible insulin therapy to conventional or “fixed” insulin therapy, the therapy had several constraints. Participants found that they had to make some adjustments to their lives to sustain this method of treatment, such as maintaining a similar weekday schedule on the weekends, adjusting food choices, or by creating food habit routines. The researchers suggested that diabetes education programs need to include interventions or strategies that can help patients successfully convert to FIIT long term.
The third group of researchers interviewed DAFNE program participants and collected information at 6 weeks and 6 and 12 months on how they assimilated course principles over time (Casey 2011). Participants initially (6 weeks) felt support from other participants, for example, by sharing experiences. However, after 6 months, participants began to value support from responsive health care professionals that focused on collaborative decision-making. The authors concluded that there is a need for diabetes educators to clearly communicate and explain to participants that adoption of the FIIT principles takes time (perhaps over 12 months). Support at 6 months appeared to be an important timeframe for participants, since motivation at this point was lowest for many.
People with insulin-requiring diabetes may also diligently perform dose calculations using their individualized algorithms when beginning intensive insulin therapy (Gross 2003). However, adherence to the ongoing determination of the prandial insulin dose may become relaxed as the person with diabetes gains familiarity with the self-adjustment of the insulin. As time passes, there may be the tendency to begin to approximate premeal doses by titrating insulin based on the “standard” or “usual” carbohydrate content of the meal. In addition, many people with insulin-requiring diabetes may actually be hesitant to take on the responsibility of increasing or decreasing their insulin doses on the basis of their carbohydrate intake and premeal blood glucose level (Gross 2003).
It is important to remember that timing of the insulin dose as well as prandial and correction algorithms are just a starting point when initiating or using insulin therapy plans for individuals with insulin-requiring type 1 or type 2 diabetes. Algorithms for flexible insulin dosing or fixed insulin dose prescriptions will not be effective if the individual self-managing his or her diabetes does not possess a thorough understanding of appropriate actions to implement. Also important is the daily incorporation of the carbohydrate-counting meal-planning approach or another method of accurately quantifying carbohydrate intake. Insulin doses need to be confirmed by one of the cornerstones of diabetes self-management—blood glucose monitoring. Finally, the individual with insulin-requiring diabetes has been shown to benefit from regular interaction with responsive and supportive diabetes health care professionals to effectively optimize blood glucose control to reduce the risk of long-term complications of poorly controlled diabetes.
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