American Diabetes Association Guide to Nutrition Therapy for Diabetes. Marion J. Franz

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