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Chapter 1 Effectiveness of Medical Nutrition Therapy in Diabetes

Joyce Green Pastors, MS, RD, CDE, and Marion J. Franz, MS, RD, CDE

Highlights

Background on Diabetes Nutrition Therapy

Evidence for the Clinical Effectiveness of MNT in Diabetes

Summary

Highlights Effectiveness of Medical Nutrition Therapy in Diabetes

• Medical nutrition therapy (MNT) for the treatment of diabetes is effective, with the greatest impact at the initial onset of diabetes. Randomized control and observational studies have shown that within the first 6 months of diagnosis, A1C can be reduced up to ~3% point reductions (range 0.23–2.6%), depending on the type and duration of diabetes. However, MNT is effective throughout the diabetes disease process, with an average reduction of A1C levels of 1–2% point reductions.

• Because type 2 diabetes is a progressive disease, an evaluation of nutrition interventions should be completed at 3 months, and if no clinical improvement has occurred, a change in treatment plan should be recommended, including the addition of oral glucose-lowering medication(s) and/or insulin.

• MNT is a process that includes a nutrition assessment, nutrition diagnosis, nutrition interventions (education, counseling, and goal-setting), and nutrition monitoring and evaluation.

• MNT provided by a registered dietitian is effective in promoting positive clinical outcomes, especially with multiple follow-up encounters involving nutrition education and counseling.

• There are many types of nutrition interventions that are effective, including decreased calorie and fat intake, carbohydrate counting, use of insulin-to-carbohydrate ratios, healthy food choices, individualized meal planning, and behavioral strategies.

• Other clinical outcomes such as improved lipid profiles, weight loss, decreased blood pressure, decreased need for medication, and decreased risk of onset and progression of comorbidities can be achieved with MNT.

Effectiveness of Medical Nutrition Therapy in Diabetes

Since the discovery of “sweet urine,” people with diabetes have been given advice on what to eat and drink, often based more on theories or beliefs than on facts. Food and nutrition advice has ranged from “starvation diets” to high- or low-carbohydrate or low-fat diets to nutritional supplements that will provide a cure.

Over the years, various diabetes organizations have published nutrition recommendations on the basis of available research and clinical observations. In recent years, the goal in the development of diabetes nutrition therapy recommendations has been to have the recommendations be based on evidence rather than theories. For example, it was longstanding advice that people with diabetes should not eat sugar or foods containing sugars. This information was based on the assumption that because sugars were small molecules, they would be absorbed rapidly, causing blood glucose levels to increase at a greater rate than starches (which are larger molecules). When research first revealed that total amounts of carbohydrate were more important than the source (Bantle 1983), the public, and many health professionals, were surprised. However, almost all diabetes nutrition recommendations now acknowledge that sugary foods can be substituted for starchy foods.

The primary goals of diabetes medical nutrition therapy (MNT) are to support the achievement and maintenance of as normal blood glucose levels as safely possible, a lipid profile that reduces the risk for cardiovascular disease, blood pressure in an ideal range, and improved or continued quality of life. Important questions then become, what is the evidence that diabetes MNT can achieve these goals and what types of MNT interventions are effective? It is important that clinicians, regardless of their field of practice, know expected outcomes from their interventions, when to evaluate such outcomes, and what interventions contribute to successful outcomes.

BACKGROUND ON DIABETES NUTRITION THERAPY

Attempts have been made to identify the efficacy and method of delivery of diabetes nutrition therapy. For example, a Cochrane review reported on a total of 18 randomized controlled trials of nutrition approaches for individuals with type 2 diabetes and, not surprisingly, could not identify one type of nutrition advice that was most effective (Nield 2007). They did report that nutrition therapy advice plus exercise was associated with a statistically significant mean decrease in A1C of 0.9% (CI 0.4–1.3) at 6 months and of 1.0% (CI 0.4–1.5) at 12 months.

A systematic review of healthy eating by the American Association of Diabetes Educators also did not reveal a clear pattern of food and nutrition interventions leading to outcomes of weight, fat intake, saturated fat, and carbohydrate. However, this review did conclude that there is a tendency for successful healthy eating interventions to include an exercise dimension and group work (Povey 2007).

Therefore, it seems clear that a single approach to diabetes MNT does not exist, just as there is no one medication or insulin regimen that applies to all people with diabetes. Instead of asking about specific eating patterns or food/nutrient interventions, this review examines the effectiveness of diabetes MNT provided by nutrition professionals (registered dietitians [RDs] or dietitians in many countries and nutritionists in some countries) and what interventions contribute to successful outcomes.

MNT for diabetes incorporates a process that, when implemented correctly, includes the following steps: 1) assessment and reassessment (for follow-up nutrition care); 2) nutrition diagnosis to identify the specific nutrition-related problems; 3) nutrition interventions that include education, counseling, and goal-setting; and 4) nutrition monitoring and evaluation, which involves monitoring progress and measuring outcome indicators (Lacey 2003). The fourth step requires that expected outcomes of nutrition interventions be known.

EVIDENCE FOR THE CLINICAL EFFECTIVENESS OF MNT IN DIABETES

The evidence for diabetes MNT comes from randomized controlled trials and observational and outcome studies showing that nutrition interventions improve metabolic outcomes, such as blood glucose and A1C, in individuals with diabetes. Randomized controlled trials are considered the gold standard for evidence. However, when assessing the impact of an intervention in clinical practice, these trials have limitations. First and foremost, subjects are selected (and rejected) usually on their perceived ability to complete the study. In clinical practice, patients are generally offered care regardless of their interest and ability to make lifestyle changes. Outcome or observational studies usually provide outcome data from all patients entered into patient care and thus are often a more realistic report on expected outcomes from clinical care. However, these studies are frequently criticized for their lack of rigorous study design. In general, useful data can be collected from both types of study designs.

Metabolic outcomes are improved in nutrition intervention studies, both when provided as independent MNT or when nutrition therapy is provided as part of overall diabetes self-management education (DSME) (Table 1.1). Studies in Table 1.1 were identified from the literature search published in the Academy of Nutrition and Dietetics (formerly the American Dietetic Association) Evidence Analysis Library (Acad Nutr Diet 2008a) and previously published articles (Franz 2008; Pastors 2002; Pastors 2003). MNT studies report the outcomes of nutrition interventions provided by an RD (or nutritionist). DSME is provided by a multidisciplinary team, which in these studies included a minimum of an RD providing nutrition therapy and a registered nurse. Studies include randomized clinical trials and longitudinal, retrospective, cohort, time series, descriptive, and observational studies. Because A1C is consistently reported across all studies, these values are included in Table 1.1. Other outcomes, as available, are also reported in Table 1.1.

Table 1.1 Summary of Evidence for Effectiveness of MNT in Diabetes

In the past decade, at least two other randomized controlled trials have been conducted involving lifestyle intervention, with both MNT and physical activity as the primary components (Look AHEAD 2007; Wolf 2004). These studies are not included in the summary of evidence in Table 1.1 because they were combined interventions and did not focus primarily on MNT as the intervention. Also, the goals for each of these studies focused on weight loss (Wolf 2004) and cardiovascular risk reduction (Look AHEAD 2007, 2010) as primary outcomes. In addition, other nutrition intervention studies have been published in the literature but are not reported in the summary of evidence because of high dropout rates or incomplete data.

Providing hospitalized patients with nutritionist visits and education can also be highly cost-effective for the health care system. In an evaluation of different types of educational visits for patients with diabetes (n = 18,404) at eight Philadelphia Health Care Centers, a total of 31,657 hospitalizations were recorded for 7,839 patients in the cohort. For patients who had at least one type of educational visit, the hospitalization rate was 34% lower than for patients who had no educational visit. Patients who had at least one visit with a nutritionist had hospitalization rates 45% lower than the rate of patients who had no educational visit. The average annual hospital charges for patients who received any educational visit were 39% less than the per-year average for patients who had no such visits (Robbins 2008).

Randomized controlled trials and other outcome studies of MNT document mean decreases in A1C of ~1–2% (up to ~3% in newly diagnosed patients), depending on the type and duration of diabetes and at what time point outcomes are reported. The evidence suggests that MNT is most beneficial at initial diagnosis, but is effective at any time during the disease process, and that ongoing evaluation and intervention are essential. Outcomes resulting from nutrition interventions are generally known in 6 weeks to 3 months, and evaluation should be performed at these times. At 3 months, if no clinical improvement has been seen in metabolic outcomes (glucose, lipids, blood pressure), usually a change in medication(s) is needed. Type 2 diabetes is a progressive disease, and as b-cell function decreases, glucose-lowering medication(s), including insulin, must be combined with MNT to achieve target goals.

Examples of Type 2 Diabetes Studies

The U.K. Prospective Diabetes Study (UKPDS) was a randomized controlled trial that involved 3,044 newly diagnosed patients with type 2 diabetes at 15 centers. All treatment and control subjects received nutrition counseling, usually from a dietitian on study entry until 3 months, at which time they were randomized into intensive or conventional therapy. During the initial period when nutrition counseling was the primary intervention, the mean A1C decreased by 1.9% (from ~9 to ~7%), and there were average weight losses of 4.5 kg (UKPDS 7 1990; UKPDS 2000). UKPDS researchers concluded that, for improved glycemia, a reduction in energy intake was at least as important, if not more important, than the actual weight lost. At 2 years, the conventional group, whose primary therapy was diet, maintained an A1C of ~7%, and even at study end, the A1C was still slightly less than at diagnosis. However, because of the progressive deterioration of diabetes control, the majority of patients needed multiple therapies to attain glycemic target levels in the longer term.

Also in the U.K. and in newly diagnosed individuals with type 2 diabetes (n = 593), the Early ACTID (Early Activity in Diabetes) trial compared usual care (initial dietitian consultation and follow-up every 6 months; control group) to an intensive nutrition intervention (dietitian consultation every 3 months with monthly nurse support) or to the latter plus a pedometer-based activity program (Andrews 2011). Baseline A1C levels were 6.7, 6.6, and 6.7%, respectively. At 6 months, A1C had not improved in the usual care group but had improved in the two intensive nutrition intervention groups (–0.3%). These differences persisted to 12 months despite the use of fewer diabetes drugs. Improvements were also seen in body weight and insulin resistance between the intervention and control groups. Of interest, adding the physical activity program created no additional benefit.

In individuals with an average duration of diabetes of 4 years, intensive nutrition therapy provided by RDs resulted in a decrease in A1C of 0.9% (8.3 to 7.4%) and in subjects with a duration of diabetes <1 year of 1.9% (8.8 to 6.9%) (Franz 1995). By 6 weeks to 3 months, it was known if nutrition intervention had achieved target goals; if it had not, the RD notified the referral source that changes in medication were needed. A1C values were maintained to 6 months.

Of interest is a randomized controlled trial of individuals with an average duration of diabetes of 9 years who had A1C levels >7% despite optimized drug therapy (Coppell 2010). The intervention group received intensive nutrition therapy resulting in a difference in A1C between the intervention and control groups at 6 months (–0.5%). This difference was highly significant, as were changes in anthropometric measurements, documenting the effectiveness of nutrition therapy even in diabetes of long duration. Furthermore, the reduction in A1C is comparable with that seen in clinical trials when a new drug, often a third, is added to conventional agents.

In another smaller randomized control trial, obese subjects receiving intensive nutrition interventions experienced a decrease in A1C of 0.6% every 2 months for up to 15 months (Laitinen 1993). Also reported was a decrease in A1C of 0.5% in patients ≥65 years of age after 10 weekly sessions with an RD emphasizing goal-setting and using learning and social cognitive theory (Miller 2002). In a study of patients with type 2 diabetes in rural Costa Rica, a decrease in A1C value of 1.8% at 3 months was reported after nutrition and exercise interventions (Goldhaber-Fiebert 2003). Also, in a study of urban African Americans, decreases in A1C at 6 months of 1.9% were shown from interventions using healthy food choices and exchange-based meal plans (Ziemer 2003). In a randomized controlled trial conducted in Taiwan, decreases of 0.7% in A1C were reported in subjects after quarterly sessions with an RD for 1 year compared to a routine care control group (Huang 2010).

A study that monitored outcomes illustrates the effectiveness of nutrition interventions in clinical practice (Lemon 2004). Data were collected from 221 patients with type 2 diabetes who were referred for nutrition education/counseling to 59 RDs working in 31 outpatient settings in the state of Wisconsin. To minimize selection bias, the RD recruited the first two patients meeting inclusion criteria each day, up to six per week. Data were collected at baseline, 3 months, and 6 months. RDs spent an average of 111 ± 55 min with each subject, they met with subjects an average of 2.1 ± 1.0 times, and 33 intervention topics were reported. Clinical outcomes (A1C, lipids, blood pressure, weight) improved significantly between baseline and 3 or 6 months, while stabilizing between 3 and 6 months. A1C decreased by 1.4% over 3 months and by 1.7% at 6 months (54% of subjects were newly diagnosed).

Examples of Type 1 Diabetes Studies

The Dose Adjusted for Normal Eating (DAFNE) trial was another study conducted in Great Britain to evaluate whether a 5-day course teaching how to adjust mealtime insulin based on planned carbohydrate intake can improve both glycemia and quality of life in individuals with type 1 diabetes (DAFNE Study Group 2002). In this study, individuals using routinely prescribed insulin therapy, in which the insulin regimen is determined first and eating must then be consistent and matched to the time actions of insulin, were either immediately provided the skills needed to determine mealtime bolus insulin doses based on desired carbohydrate intake on a meal-to-meal basis or they attended the training 6 months later. In the group receiving the DAFNE training, A1C levels were significantly improved by 1%, with no significant increase in severe hypoglycemia, along with positive effects on quality of life, satisfaction with treatment, and psychological well-being. These results occurred despite an increase in the number of insulin injections (but not in total amount of insulin) and an increase in blood glucose monitoring compared with the control subjects who received the training later.

A follow-up of original trial participants at a mean of 44 months documented a mean improvement in A1C from baseline of 0.4%, remaining significant but less than the 12-month levels. Improvements in quality of life seen at 12 months were well maintained over ~4 years (Speight 2010). Of interest is another follow-up report examining changes in food and eating practices in DAFNE trial participants after changing to flexible, intensive insulin therapy. Concern had originally been expressed that individuals with type 1 diabetes, if given the freedom to adjust insulin doses based on carbohydrate intake, would overeat or make unhealthy food choices. These concerns were unfounded, since individuals using flexible, intensive insulin therapy did not engage in more excessive or unhealthy eating. Instead, many of the participants reported making few eating changes and, in some cases, actually reported being more rigid in their eating habits (Lawton 2011).

A group in Germany reported a 1.5% lower A1C level 1 year after a 5-day intensive training course (after which the DAFNE trial was modeled) teaching participants how to match insulin doses to their food choices while keeping their blood glucose level close to normal. The course was taught by specially trained dietitians and nurse educators (Pieber 1995). Improvements were maintained to 3 years without increasing the risk of hypoglycemia (Sämann 2005). A similar program in Australia teaching carbohydrate counting and insulin dose adjustment to patients with type 1 or type 2 diabetes and taught by dietitians and doctors also prompted good results. Participants reported A1C levels fell from 8.7% initially to 8.1% at 12 months (Lowe 2008).

The role of nutrition behaviors in achieving glycemic control in 623 intensively treated patients in the Diabetes Control and Complications Trial (DCCT) was examined. The four nutrition behaviors associated with a clinically significant reduction in A1C (0.9%) were as follows: adhering to the prescribed meal and snack plan, adjusting insulin dose in response to meal size, promptly treating hyperglycemia, and avoiding overtreatment of hypoglycemia (Delahanty 1993).

Nutrition Therapy Clinical Effectiveness Studies

Nutrition therapy for diabetes is clinically effective. Randomized controlled trials and observational outcome studies have documented decreases in A1C of ~1–2% (range –0.5% to –2.6%), depending on the type and duration of diabetes. These outcomes are similar to those from oral glucose-lowering medications.

Although attempts are often made to identify one approach to diabetes MNT, a single approach does not exist. Research shows that there are many types of nutrition interventions that are effective. Interventions include reduced energy/fat intake, carbohydrate counting, simplified meal plans, healthy food choices, individualized meal-planning strategies, exchange choices, use of insulin-to-carbohydrate ratios, physical activity, and behavioral strategies. In reviewing consistent themes for nutrition intervention, it appears that, for individuals with type 2 diabetes, reducing the energy content of usual food intake is central to successful outcomes. For individuals with type 1 diabetes, adjusting insulin doses for planned carbohydrate intake is of primary importance.

Central to these interventions are multiple encounters to provide education and counseling initially and on a continued basis. The number and duration of MNT encounters may need to be greater if the patient has language, ethnic, or cultural concerns; if changes in medications (such as addition of glucose-lowering medications or insulin therapy in type 2 diabetes or changes in insulin regimens in type 1 or type 2 diabetes) are made; or for weight management. Nutrition education and counseling must be sensitive to the personal needs and cultural preferences of the individual and his or her ability and willingness to make changes.

At ~6 weeks after the initial nutrition encounter, it should be determined whether the individual is making progress toward personal goals. If there is no evidence of progress, the individual and nutrition professional need to reassess and consider possible revisions to the nutrition care plan. At 3 months, changes in medical therapy (medications added or adjusted) need to be made if blood glucose concentrations or A1C percentages have not shown a downward trend; the patient has lost weight with no improvement in glucose; the patient is doing well with lifestyle changes and further interventions are unlikely to improve medical outcomes; or if the patient has done all that he or she can or is willing to do.

How often nutrition education and counseling needs to be implemented is unknown at this time. Evaluating the effectiveness of diabetes MNT is performed at 3, 6, or 12 months and usually includes the initial series of encounters. The number of initial and follow-up sessions varies in all the studies. It can be speculated that just as it is important for individuals with diabetes to be seen on a regular basis for medical care, it is also important for individuals to receive continuing education, counseling, and support for lifestyle changes. The Academy of Nutrition and Dietetics nutrition practice guidelines for type 1 and type 2 diabetes recommends at least one follow-up encounter annually to reinforce lifestyle changes and to evaluate and monitor outcomes that affect the need for changes in MNT (or medication) (Acad Nutr Diet 2008a). For example, children and adolescents often require MNT changes because of growth or other lifestyle factors. Patients with type 2 diabetes often require the addition of or changes in medication. The RD can also assist physicians and other health care providers by helping patients understand and accept the reasons for management changes.

Other important clinical outcomes that need to be evaluated, in addition to A1C levels, are lipids and blood pressure. In studies done primarily in individuals without diabetes, cardioprotective nutrition therapy implemented by RDs resulted in a reduction of serum total cholesterol by 7 to 21%, LDL cholesterol by 17 to 22%, and triglycerides 11 to 31% (Acad Nutr Diet 2011). Pharmacological therapy changes should be considered if goals are not achieved between 3 and 6 months after initiating MNT.

Nutrition therapy is also effective in reducing blood pressure in both normotensive and hypertensive adults. Substantial reductions in blood pressure that are clinically relevant are reported from implementation of multiple lifestyle interventions (Appel 2006). Nutrition therapy recommendations (weight loss, sodium reduction, increased physical activity, and following the DASH diet [Dietary Approaches to Stop Hypertension] [rich in fruits, vegetables, and low-fat dairy products but low in saturated and total fat]) in hypertensive individuals not on medication reduced systolic blood pressure by 14.2 mmHg and diastolic blood pressure by 7.4 mmHg and in nonhypertensive individuals reduced systolic blood pressure by 9.2 mmHg and diastolic blood pressure by 5.8 mmHg (Appel 2003). However, generally, studies implementing MNT for hypertension implemented by RDs report an average reduction in blood pressure of ~5 mmHg in both systolic and diastolic blood pressure (Acad Nutr Diet 2008b).

SUMMARY

• For individuals with type 2 diabetes, attention to food intake and patterns of eating are important for the management of diabetes, even if on medications, including insulin.

• For individuals with type 1 diabetes, matching insulin doses to planned carbohydrate intake is important for the management of diabetes.

• Nutrition education and counseling is best provided in a series of encounters—usually one initial encounter with two or three follow-up encounters, which can be implemented individually or in groups. The dietitian (or nutritionist) should determine if and when additional encounters are needed.

• Ongoing nutrition education and counseling is needed yearly, or more often as required or requested, or when changes in medication are made.

• A variety of nutrition interventions can be implemented depending on which are best suited to the needs of the individual patient. For patients with type 2 diabetes, the focus should be on reducing or maintaining a reduced energy intake. For patients with type 1 diabetes, a primary focus for educating patients is on how to adjust insulin doses on the basis of planned carbohydrate intake.

• Blood glucose monitoring and A1C results can be used to evaluate the effectiveness of MNT; lipids and blood pressure outcomes also require monitoring and evaluation.

• To successfully integrate MNT into overall diabetes management, an interdisciplinary team approach is essential.

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Joyce Green Pastors, MS, RD, CDE, is an Assistant Professor of Education, Internal Medicine, Virginia Center for Diabetes Professional Education, University of Virginia Health System, Charlottesville, VA. Marion J. Franz, MS, RD, CDE, is a Nutrition/Health Consultant at Nutrition Concepts by Franz, Inc., Minneapolis, MN.