Nutrition therapy for diabetes: effectiveness, carbohydrates and alcohol

Abstract

Studies documenting the effectiveness of medical nutrition therapy for Type 1 and Type 2 diabetes report improvements in hemoglobin A_1C (A1C), as well as in other outcomes. A variety of nutrition therapy interventions are effective. Under debate is the role of carbohydrate intake on glycemic control and weight loss in individuals with Type 2 diabetes. Some studies have reported improvements in glycemic control from reducing carbohydrate intake; however, other trials have reported no significant changes in A1C with a lower carbohydrate eating pattern. Studies comparing low-carbohydrate or low-fat diets for weight loss at 12 months report similar amounts of weight loss. Evidence for the usefulness of the glycemic index concept is debatable. For the majority of people with diabetes moderate alcohol consumption with food will have minimal, if any, acute or long-term effects on glycemic control, and may have beneficial effects on insulin sensitivity and decreased risk for coronary heart disease.

Keywords::

• alcohol
• coronary heart disease
• glycemic control
• glycemic index
• high- or low-carbohydrate
• nutrition therapy
• Type 1 and Type 2 diabetes
• weight management

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Release date: 20 November 2012; Expiration date: 20 November 2013

Learning objectives

• Upon completion of this activity, participants will be able to:

• • Assess the role of medical nutrition therapy among patients with diabetes

• • Analyze the effects of dietary carbohydrate among patients with diabetes

• • Evaluate the meaning of the glycemic index

• • Distinguish the effects of alcohol consumption among patinets with diabetes

Financial & competing interests disclosure

EDITOR

Elisa Manzotti

Publisher, Future Science Group, London, UK

Disclosure: Elisa Manzotti has disclosed no relevant financial relationships.

CME AUTHOR

Charles P. Vega, MD

Health Sciences Clinical Professor; Residency Director, Department of Family Medicine, University of California, Irvine, CA, USA.

Disclosure: CP Vega has disclosed no relevant financial relationships.

AUTHORS AND CREDENTIALS

Marion J Franz, MS, RD, CDE

Nutrition Concepts by Franz Inc., Minneapolis, MN, USA.

Disclosure: Marion J Franz has disclosed no relevant financial relationships.

Historically, professional diabetes organizations, including the American Diabetes Association (ADA), have attempted to define an ‘ideal’ nutrition prescription for diabetes. This prescription was applied to all persons with diabetes and would identify recommended percentages of carbohydrate, protein and fat and calorie levels. The problem with this approach was that the prescribed ‘diet’ could not be individualized and often lacked relevance to the personal lifestyle, cultural or socioeconomics of the individual with diabetes. Therefore, in 1994 the ADA recommended an individualized nutrition prescription be developed based on the metabolic profile, treatment goals and lifestyle changes the person with diabetes was willing and able to make, and not on rigid predetermined calorie levels and macronutrient percentages [1]. This was reaffirmed in the 2008 ADA’s position statement for diabetes nutrition recommendations and interventions that stated: “Numerous studies have attempted to identify the optimal mix of macronutrients for the diabetic diet, however, it is unlikely that one such combination of macronutrients exists … medical nutrition therapy (MNT) for diabetes must address individual needs, taking into account personal and cultural preferences and willingness to change” [2]. The Academy of Nutrition and Dietetics (formerly the American Dietetic Association; Acad Nutr Diet) also concluded that: “Evidence for differing percentages of carbohydrate and macronutrients in the food/meal plan is inconclusive” [3,101]. However, researchers and professionals still attempt to identify ideal nutrition prescriptions for people with diabetes.

To implement nutrition therapy for diabetes it is essential to have evidence that nutrition therapy interventions are effective. The primary goal for diabetes nutrition care is to integrate nutrition therapy into the management of diabetes, thus improving glucose, lipid and blood pressure control, and reducing the risk of potential long-term complications of diabetes and cardiovascular disease (CVD) [4,5]. Weight management is another goal for the prevention of diabetes and the management of Type 2 diabetes [6,7]. How best to achieve these goals has been, and remains, controversial.

As do all fields of medicine, the field of nutrition therapy now uses an evidence-based approach to make recommendations for nutrition care. This approach requires that key questions and research criteria be identified. This is followed by a review of the evidence and writing of summary statements from which evidence-based nutrition recommendations and practice guidelines are written. Box 1 lists summary statements used to write the MNT recommendations and practice guidelines for Type 1 and Type 2 diabetes in adults by the Acad Nutr Diet [3,101]. The ADA has also published evidence-based recommendations for the role of macronutrients [8] and a textbook that examines evidence for diabetes nutrition therapy interventions [9].

This article reviews three important questions evaluated in these publications:

• • Is diabetes nutrition therapy effective and what are expected outcomes from nutrition interventions?

• • Is there an optimal carbohydrate ratio and/or type for glucose and weight management?

• • Is alcohol consumption beneficial or harmful?

Effectiveness & outcomes from MNT for diabetes

The evidence for diabetes MNT comes from randomized controlled trials (RCTs), and observational and outcome studies showing that nutrition interventions improve metabolic outcomes, such as blood glucose, hemoglobin A_1c (A1C), lipids, blood pressure, weight and/or quality of life in individuals with diabetes [10]. Studies of MNT document mean decreases in A1C of approximately 1–2% (range: 0.23–2.6%) depending on the type, duration and baseline A1C, and at what time point in the disease process 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 support are essential. Outcomes resulting from nutrition interventions are generally known by 6 weeks to 3 months and evaluation should be performed at this time. At 3 months, if patients have made the lifestyle changes they are able or willing to make, and if target goals have not been achieved, changes in medication(s) is usually needed. In Type  1 diabetes, evaluation and changes in the insulin regimen are generally required. In Type 2 diabetes, because it is a progressive disease, as β-cell function declines, glucose-lowering medications, including insulin, must be combined with MNT to achieve target goals. However, MNT continues to be effective, safe and relatively affordable throughout the disease process and therefore requires continued implementation and support. Although MNT has a major impact on glucose control, it also plays an important role in the management of blood pressure and lipids.

For example, studies in Type 2 diabetes have demonstrated decreases in A1C of approximately 2% from MNT in newly diagnosed patients having an A1C level of approximately 9% [11,12]. Researchers in the UK Prospective Diabetes Study (UKPDS) concluded that the reduction in energy intake was at least as important, if not more important, than the actual weight loss, as blood glucose levels improve almost immediately when patients make changes in eating patterns and before much weight is lost. At 2 years, the improvement in A1C from the nutrition intervention was maintained [11]. In another study in newly diagnosed patients with Type 2 diabetes and with an A1C level of approximately 6.7%, an intensive nutrition intervention lowered A1C by 0.3% [13]. This was significant (p < 0.001) and persisted to 12 months even with use of fewer diabetes drugs, and illustrates the effect of baseline A1C levels and potential outcomes from MNT.

In individuals with an average duration of diabetes of 4 years, intensive MNT resulted in a decrease of A1C of approximately 1%. By 6 weeks, it was known if nutrition interventions were effective in achieving target goals or if changes in medication were needed [12]. A study illustrating the effectiveness of MNT by registered dietitians in clinical practice documented significant improvements in A1C (an average decrease of ~1.6%), lipids, blood pressure, weight between baseline and 3 months, while stabilizing between 3 and 6 months [14]. Of interest is a RCT of patients with an average duration of diabetes of 9 years who had A1C levels >7% despite optimized drug therapy. Intensive MNT resulted in a difference in A1C between the intervention and control groups at 6 months of 0.5% (p = 0.007) [15]. The reduction in A1C is comparable with adding a new drug, often a third and at less cost, and illustrates the value of MNT even in diabetes of long duration.

In patients with Type 1 diabetes, MNT using insulin-to-carbohydrate ratios improved A1C levels by 1% with no significant increase in severe hypoglycemia, along with positive effects on quality of life, satisfaction with treatment and psychological well-being, despite the increase in the number of insulin injections (but not in the total insulin dose) and blood glucose monitoring compared with controls [16]. Improvements in A1C and quality of life remained significant over approximately 4 years [17].

The above are examples of MNT in Type 1 and Type 2 diabetes and effectiveness in improving glycemic control. MNT also has beneficial effects on lipids, blood pressure and weight [10]. In these studies, many types of nutrition interventions are shown to be 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. For patients with Type 2 diabetes, nutrition intervention in these studies focuses on reduced energy intake and for patients with Type 1 diabetes the nutrition intervention focuses on educating patients on how to adjust insulin based on planned carbohydrate intake. Use of cognitive behavioral therapy involving patients with diabetes has resulted in improvements in weight loss, glycemic control and lipid levels; however, sustaining clinically significant outcomes can be problematic [18]. In addition to the importance of selecting nutrition interventions depending on which are best suited to the needs of the individual patient, a series of initial encounters for nutrition education and counseling and follow-up support is essential [10]. If patients have language, ethnic or cultural concerns, if changes in medications are made or for weight management, the number and duration of nutrition care encounters will need to be greater [3–5]. Furthermore, to successfully integrate MNT into overall diabetes management, an interdisciplinary team approach is required.

Carbohydrate intake & diabetes management

Historically, carbohydrate has been the macronutrient of controversy with high or low amounts and types – sugar versus starch, high or low glycemic index (GI) eating patterns – being debated. The first ‘rule’ given to people with diabetes was usually that they should not eat sugar, in any form or amount, because it was a small molecule and would be absorbed into the blood quickly causing blood glucose levels to ‘soar’. When research proved this to be wrong [19], the public as well as health professionals found it hard to believe that the amount of carbohydrate eaten (total grams) was more important than the type. Although both the quantity and type or source of carbohydrates found in foods can influence postprandial glucose levels, the ADA concluded that monitoring total carbohydrate is a key strategy in achieving glycemic control [4].

Before reviewing the evidence regarding the debate on low-carbohydrate diets, it should be noted that the majority of people with diabetes do not eat either a high- or low-carbohydrate diet. Both people with Type 1 and Type 2 diabetes are reported to eat moderate amounts of carbohydrate [20,21]. Furthermore, it appears difficult for persons with Type 2 diabetes to eat a high-carbohydrate diet. In the UKPDS, despite receiving individual education from dietitians on the recommended carbohydrate intake of 50–55% of total energy intake, patients reported an energy intake from carbohydrate of 43%, which was similar to that of the general public [22]. Vegans or vegetarians are perhaps the primary people with diabetes who tend to eat a higher carbohydrate diet (~65–75% of total energy), which is reported to improve glycemic control as well as lipids and blood pressure [23].

Carbohydrates & glycemia

Under discussion are two questions: does eating a low-carbohydrate diet improve glycemic control and does eating a low-carbohydrate diet improve weight loss diet outcomes? Two observational studies have examined the association between carbohydrate intake and A1C levels in persons with Type 1 and Type 2 diabetes [20,24]. In the cross-sectional Strong Heart Study [24], lower intake of carbohydrate (<35–40% of energy) and higher intakes of total fat (>25–30% of energy) and saturated fatty acids (>10% of energy) were associated with poorer glycemic control (p < 0.01 for all). Similarly, in persons receiving intensive treatment in the Diabetes Control and Complications Trial, dietary data through 5 years of follow-up reported that a lower carbohydrate intake (37%) and a higher total fat (45%) and saturated fat (17%) intake were associated with worse glycemic control compared with a higher carbohydrate (56%) intake (A1Cs of 7.0 vs 7.5%, respectively) [20]. The authors suggest that the carbohydrate content is less important than the total and saturated fat content, to which it is usually inversely related. They note that high-fat meals have been shown to interfere with indexes of insulin signaling, which results in a transient increase in insulin resistance [25], and that lower fat diets reduce basal free fatty acid concentrations and improve peripheral insulin sensitivity in Type 1 diabetes [26].

The ADA’s systematic review of macronutrients reviewed 11 clinical trials examining the effects of lowering total carbohydrate intake on glycemic control in individuals with diabetes [8]. A1C decreased with a lower carbohydrate diet in six out of ten studies in which it was measured. They note that although reducing total carbohydrate intake improved markers of glycemic control and insulin sensitivity, the studies were small, of short duration, and in some cases were not randomized or had high dropout rates. They also noted that three RCTs found no statistically significant changes in A1C with a very low-carbohydrate diet [27–29] and one found no difference with a moderately low-carbohydrate diet [30].

A meta-analysis of 19 short-term studies (from 10 days to 6 weeks) including 306 persons with Type 2 diabetes compared lower-carbohydrate, higher fat (40%/40%) to higher carbohydrate, lower fat (58%/24%) diets, and found no significant differences between diets in reducing A1C and total and LDL-cholesterol [31]. The higher carbohydrate diets did increase triglyceride levels and decrease HDL-cholesterol. However, the higher carbohydrate diets did not increase triglyceride, levels when energy restriction was prescribed. After publication of the meta-analysis, three 1-year studies in persons with Type 2 diabetes comparing higher carbohydrate diets to lower carbohydrate/high monounsaturated fat diets [30,32] or a low-carbohydrate Atkins diet [28] reported no differences in A1C, weight loss, LDL-cholesterol, triglycerides or blood pressure.

Carbohydrates & weight management

The rationale for the use of low-carbohydrate diets for weight loss is that with carbohydrate restriction, fuel sources shift from glucose and fatty acids to fatty acids and ketones, leading to appetite restriction, weight loss, and improvements in glycemic control and risk markers for CVD [33]. A meta-analysis of RCTs (n = 5,447 overweight and obese adults) compared effects of low-carbohydrate versus low-fat diets on weight loss and CVD risk factors [34]. After 6 months, individuals in the low-carbohydrate group had lost the most weight (-3.3 kg), but at 12 months weight loss was similar. Total and LDL-cholesterol changed more favorably in individuals assigned to low-fat/higher carbohydrate diets, whereas HDL-cholesterol and triglyceride values changed more favorably in individuals in the low-carbohydrate group. Blood pressure changes were similar between groups. Thus, neither diet showed a clear benefit on CVD risk factors.

A 6-month study in persons with Type 2 diabetes compared a low-carbohydrate ketogenic diet (LCKD) with a low-GI, reduced-calorie diet [35]. Both groups experienced weight loss and improvements in A1C, fasting insulin and HDL-cholesterol, but the improvements were greater in the LCKD group. However, the improvements may be temporary. A 48-week trial of an LCKD diet versus a low-fat diet plus orlistat by the same investigators reported similar improvements in weight, A1C, insulin and lipids at study end [36].

Other trials have also shown that the key to weight loss is reduced energy intake and not the macronutrient composition or type of diet [37,38]. During the first 6 months of dieting, participants in weight loss trials lose 5–9% of their baseline weight. At approximately 6 months, regardless of the diet, weight plateaus. With continued support, 3–6% of weight loss can be maintained to approximately 4 years [39]. Fortunately, it is this amount of weight loss that has important health benefits, including prevention of Type 2 diabetes, decreases in blood pressure, decreases in circulating inflammatory makers (C-reactive protein and cytokines), and potential improvements in lipids [40]. The benefits of modest weight loss are an important public health message.

Glycemic Index

The GI measures the relative area under the glucose curve of 50 g of digestible carbohydrate compared with 50 g of either glucose or bread. It does not measure how rapidly blood glucose levels increase after eating carbohydrate-containing foods. This common inaccurate definition of the GI implies that a high-GI food peaks quickly and a low-GI food peaks later. A review compared different types (e.g., breads, cereals, potatoes and pasta, fruit and fruit juice) of low- medium- and high-GI foods and glucose responses in persons without diabetes. Glucose peaks occurred consistently at approximately 30 min, regardless of the food’s GI, with a modest difference in glucose peak values between high- and low-GI foods [41]. The high-GI foods did produce a faster rise in the peak glucose response (i.e., 41 vs 32 mg/dl) but the peak occurred at the same time (obviously the glucose level must go up fasting to get to 41 mg/dl than to 32 mg/dl at the same time). However, this is not the usual interpretation when the public hears ‘fast-acting’.

A major problem with the GI is the variability of GI responses from carbohydrate-containing foods within and among individuals. For example, the mean glycemic response and standard deviation of 50 g of carbohydrate from white bread tested in 23 subjects was 78 ± 73, with an inter-individual coefficient of variation (CV) of 94%. The range of GI values obtained for bread was broad, ranging from 44 to 132 for the mean of three tests with a CV of 30% [42].

The estimated glycemic load (GL) of foods, meals and eating patterns is calculated by multiplying the GI of each food by the grams of carbohydrate for the food consumed and then totaling the GL values for all foods in a meal. The GL is used most often in research studies, especially in epidemiological studies. Because of the calculations needed, it is not likely to be a very useful approach for individuals to use in planning meals or prandial insulin doses.

After reviewing 15 studies comparing high versus low-GI diets, the Acad Nutr Diet Evidence-Based Nutrition Practice Guidelines concluded that: “Studies comparing high- versus low-GI diets report mixed effects on A1C levels. These studies are complicated by differing definitions of high-GI or low-GI diets or quartiles, as well as possible confounding dietary factors” [3,101]. Of the 15 studies reviewed, 12 were of short duration (<3 months) with a limited number of subjects. Only three studies were of 1-year duration [30,43,44]. After 1 year, two studies reported no differences in A1C between the low-GI and control groups [30,43], and one study reported no difference in actual diet GIs between the low-GI and control groups [44].

The ADA systematic review concluded: “In general, there is little difference in glycemic control and CVD risk factors between low-GI and high-GI or other diets. A slight improvement in glycemia may result from a lower GI diet; however, confounding by higher fiber must be accounted for in some of these studies” [8]. Furthermore, as with carbohydrate, most individuals with diabetes appear to consume a moderate GI diet and it is unknown whether reducing the usual GI by a few units will result in improved long-term glycemic control. As a result, the ADA has deleted a statement in their nutrition recommendations implying modest benefit from the GI/glycemic load [102].

Carbohydrate summary

Although observational studies report A1C benefits from a higher carbohydrate, low-fat eating pattern, in clinical trials both high- and low-carbohydrate eating patterns lead to similar improvements in A1C and bodyweight. It appears likely that total energy intake outweighs the distribution or type of carbohydrate. Evidence for the usefulness of the GI concept is unequivocal. Therefore, it would seem appropriate to recommend an eating pattern with moderate amounts of carbohydrate (which is how many people with diabetes already eat) and that includes nutrient-dense fruits, vegetables, whole grains, legumes and low-fat dairy foods – all carbohydrate sources and important components of a healthy eating pattern [103]. Nutrient-dense foods are foods and beverages that have not been ‘diluted’ with the addition of added solid fats and added sugars. For people with diabetes, these foods should be included in appropriate amounts and portion sizes in a food/meal plan.

For persons with Type 2 diabetes total energy intake is important, and therefore careful attention to amounts and portion sizes is critical. For persons with Type 1 (or Type 2) diabetes who adjust their prandial insulin doses, insulin doses should be adjusted to match carbohydrate intake (insulin-to-carbohydrate ratios). For all, monitoring total carbohydrate intake whether by carbohydrate counting, choices or experience-based estimation remains a key strategy in achieving glycemic control [4]. Consistency in carbohydrate intake on a day-to-day basis is also reported to be beneficial.

Alcohol: benefits & risks for people with diabetes

Observational and small clinical trials have reported beneficial effects of moderate alcohol consumption in persons with diabetes. A large cross-sectional study of adults with diabetes (n = 38,564) reported that alcohol consumption was linearly and inversely associated with A1C levels; however, with three or more drinks per day, A1C levels began to increase [45]. NHANES III data from adults with diabetes reported that those who had 30 or more drinks of alcohol per month, compared with nondrinkers, had average A1C levels 1.2% lower than other adults with diabetes [46]. However, it is also reported that there is an increase in risk for poor adherence to diabetes self-care behaviors with increasing alcohol consumption, starting with those who consume one drink per day [47]. Thus, the emphasis is on encouraging moderate and sensible alcohol use in persons with diabetes, if it is their choice to consume alcohol.

In persons with Type 2 diabetes, acute and longer term moderate consumption of alcoholic beverages appears to have no detrimental effect on glucose control or insulin levels. Two clinical trials examined the effect of alcohol in persons with diabetes [48,49]. In the first study, after 3 months, one drink per day of wine decreased fasting plasma glucose by approximately 22 mg/dl compared with a nonalcoholic beverage [48]. In the second study, wine (6.5 oz) per day for 30 days compared with abstinence had no effect on glucose or lipids but did improve insulin sensitivity [49]. A systematic review of earlier, small, acute studies also concluded that moderate consumption of alcohol does not acutely impair glycemic control in persons with Type 2 diabetes and may actually result in a small decrease in glucose concentration [50]. However, chronic ingestion (>45 g/day) has been shown to cause deterioration in glucose control; the effects from excess alcohol are reversed after abstinence for a number of days.

In persons with Type 2 diabetes, moderate alcohol consumption is also associated with decreased coronary heart disease risks and decreased total mortality. The type of alcoholic beverage does not influence beneficial effects [50–52]. The most consistent mechanism for the beneficial effects of alcohol is an increase in insulin sensitivity. However, improvements in markers of inflammation and endothelial dysfunction are also reported [51]. Improvements in HDL-cholesterol have been mixed [49]. Available evidence suggests that moderate alcohol intake has no detrimental effect on triglyceride levels [49,53–57]. For example, in men with Type 2 diabetes, light drinkers (<14 drinks per week) had average triglyceride levels of 115 mg/dl compared with 132 mg/dl in nondrinkers and 170 mg/dl in heavy drinkers (>14 drinks per day) [57].

In persons with Type 1 diabetes, moderate consumption of alcoholic beverages appears to have minimal, if any, acute affects on glucose levels and insulin needs. However, of concern is the reporting of late-onset hypoglycemia after drinking alcoholic beverages, likely due to reduced growth hormone levels after alcohol consumption [58,59]. Thus, the importance of repeated self-monitoring of blood glucose levels after drinking alcohol to determine if treatment for hypoglycemia is needed. In persons with Type 1 diabetes, moderate alcohol consumption has also been associated with lower risk of microvascular complications [60].

For the majority of people with diabetes, moderate alcohol consumption with food will have minimal, if any, acute or long-term effects on glycemic control, and may have beneficial effects on insulin sensitivity and decreased risk for coronary heart disease [61]. Abstention from alcohol should be advised for individuals who cannot restrict their drinking to moderate levels, children and adolescents, individuals who take prescription or over-the-counter medications that can interact with alcohol, and individuals with medical problems such as liver disease, pancreatitis, advanced neuropathy or severe hypertriglyceridemia. In addition, alcohol should be avoided by women who are pregnant or who are unsure if they are pregnant, and by individuals who plan to drive, operate machinery, or take part in activities that require attention, skill or coordination [2].

The data, however, do not support recommending alcohol consumption to individuals with or at risk for diabetes who do not currently drink as only observational studies and small clinical trials documenting the effects of alcohol are available [2]. If individuals with diabetes choose to consume alcohol, it should be in moderation, and only by adults. The 2010 Dietary Guidelines for Americans define moderate alcohol consumption as the average daily consumption of up to one drink per day for women and up to two drinks per day for men, and no more than three drinks in any single day for women and no more than four drinks in any single day for men [103].

The type of alcohol-containing beverage consumed does not make a difference. One drink is commonly defined as 12 oz. of beer, 5 oz. wine or 1.5 oz. of 80-proof distilled spirits, each of which contains approximately 15 g of alcohol. Because alcohol does not affect blood glucose levels or require insulin to be metabolized, occasional use of alcoholic beverages can be considered an addition to the regular food/meal plan and no food should be omitted. For persons using insulin or insulin secretagogues, alcohol should be consumed with food to prevent hypoglycemia.

Expert commentary & five-year view

This review has focused primarily on three issues related to diabetes nutrition therapy: effectiveness, carbohydrates and alcohol. Effectiveness was selected because, as with all medical interventions, it is essential to know the potential outcomes from an intervention, what contributes to the effectiveness of an intervention, and when to evaluate effectiveness. Research conducted internationally has demonstrated the current answers to these issues in regard to nutrition therapy for diabetes. Because of the importance of this issue, it is essential that this type of research continue. RCTs are considered the gold standard for evidence. However, when assessing the impact on an intervention in clinical practice, these trials have limitations. First, subjects are selected (and rejected) based on their perceived ability to complete the study. In clinical practice, patients are generally provided with 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 interventions such as nutrition therapy. However, these studies are frequently criticized for their lack of rigorous study design. Useful data can be obtained from both types of study designs, and therefore both RCT and outcome or observational study data should continue to be collected in the future.

The macronutrient composition for a food/meal plan for persons with diabetes continues to be controversial. As reviewed, research has largely focused on carbohydrates with minimal research on protein and fat. As no clear ideal percentages of carbohydrate, protein and fat exist, the nutrition prescription for individuals is best based on an appropriate energy intake and a healthy eating pattern. Individuals with both Type 1 and Type 2 diabetes report following a moderate carbohydrate-eating pattern (~45% of total energy intake), which appears to be of less importance than total energy intake. However, the balance between carbohydrate consumed and available insulin does predict glycemic response, so monitoring carbohydrate intake remains a key strategy in achieving glycemic control [4,101].

Research on the role of protein and fat in diabetes nutrition therapy is limited. In people with Type 2 diabetes, ingestion of protein results in acute insulin and glucagon responses with minimal, if any, postprandial glucose or lipid responses [2,62]. Gram for gram carbohydrate and protein require equal acute amounts of insulin for metabolism. Recent research has focused on higher protein and lower carbohydrate diets for beneficial effects on glycemia and CVD risk factors. Studies thus far have been of short duration with small numbers of subjects with diabetes. Although beneficial outcomes have been reported, the ability of persons living in the ‘real’ world to increase protein by food long term is unknown.

Although it is often stated that dietary fats slow glucose absorption and delay the peak glycemic response, evidence to support this statement is difficult to find. In acute studies with limited numbers of subjects, the addition of fat to meals appears to have minimal effects on postprandial glucose [62]. Epidemiological and clinical trials have reported that long-term intake of higher levels of total fat, especially saturated fatty acids, results in greater whole-body insulin resistance. The acute and long-term effects of various levels of dietary fat intake on glucose and insulin outcomes are areas requiring research.

Alcohol was the third topic selected for review. If people with diabetes choose to drink alcoholic beverages, it is important they know what effect it can have on blood glucose control and the management of diabetes and how to drink safely. Moderate alcohol consumption is also associated with reduced risk of and mortality from coronary heart disease and lower total mortality rates. The mechanism for this benefit is unclear. Continued research on the consumption of alcohol and diabetes is warranted.

The role of weight loss in the management of Type 2 is also controversial. For prevention or delay of onset and for improvement in insulin resistance early in the progression of Type 2 diabetes, modest weight loss, along with regular physical activity, is beneficial. However, as the disease progresses and insulin deficiency becomes more prominent, weight loss is less likely to be of benefit. Because of the insulin deficiency, weight loss may even occur without effort. In weight loss trials of 1-year duration or longer conducted in subjects with diabetes, approximately half of the studies reported improvements in A1C whereas half reported no improvement in A1C, despite similar weight losses [3,101]. The Look AHEAD trial, which is designed to assess if weight reduction combined with physical activity can reduce CVD morbidity and mortality in individuals with Type 2 diabetes, has, however, reported very successful outcomes at 4 years [7]. Whether a very intensive lifestyle intervention that appears to be necessary for success can be implemented in clinical settings is another important research question. Furthermore, because improvement in glycemia occurs almost immediately, and before much weight is lost, are the improvements due to the reduced energy intake or to weight loss?

As reviewed, strong evidence supports the effectiveness of MNT for diabetes, but individuals with diabetes require continued education and support to maintain successful lifestyle interventions. How best to provide this clinically is perhaps the most important question for the future.

Box 1. Academy of Nutrition and Dietetics evidence review summary statements used to write medical nutrition therapy recommendations and the nutrition practice guidelines for Type 1 and Type 2 diabetes in adults.

Summary statements. Grade^† in parenthesis

• •Carbohydrate

  • –Carbohydrate intake: consistency in the amount and distribution of carbohydrate intake on a day-to-day basis is associated with improvement in glycemic control in persons on medical nutrition therapy (MNT) alone, glucose-lowering medications, or fixed insulin doses (II)

  • –Carbohydrate intake: adjusting mealtime insulin to match planned carbohydrate intake in persons with Type 1 diabetes results in improved glycemic control (I)

  • –Sucrose: intakes of 10–35% of total energy do not have a negative effect on glycemic or lipid responses when sucrose is substituted for isocaloric amounts of starch (I)

  • –Glycemic index: studies comparing high- versus low-glycemic index diets report mixed effects on A1C levels (II)

  • –Fiber: the evidence is inconclusive that increasing dietary fiber will influence glycemic outcomes; however, there is conclusive evidence that higher fiber eating patterns will lower total cholesterol compared with lower fiber eating patterns (I)

• •Protein

  • –The amount of protein consumed has minimal influence on glycemic or lipid responses, and shows no long-term effect on insulin requirements (II)

  • –In persons with diabetic kidney disease, improvements in albumin excretion rate are reported with protein intake <1 g/kg/day, but no improvements in glomerular filtration rate. Malnutrition has been reported with a protein intake of approximately 0.7 g/kg/day (II)

• •CVD

  • –Cardioprotective nutrition interventions reduce A1C, blood pressure and bodyweight, and improve serum lipid profiles, all of which reduce risk of CVD (I)

  • –In persons with diabetes and CVD, cardioprotective nutrition interventions improve endothelial health, lipid profiles and blood pressure (I)

• •Weight management

  • In weight loss randomized controlled trials, approximately half report improvements in A1C values with weight loss, whereas approximately half report no improvement in A1C values despite fairly similar weight losses. Randomized controlled trials using weight loss medications report consistent improvements in A1C (II)

• •Physical activity

  • –In persons with Type 2 diabetes, 90–150 min of weekly physical activity (both aerobic and resistance/strength training) reduces A1C, improves insulin sensitivity and decreases risk for all-cause mortality (I)

  • –In persons with Type 1 diabetes, glycemic control generally does not improve in response to ongoing participation in physical activity alone (II)

• •Effectiveness of medical nutrition therapy (MNT)

  • Medical nutrition therapy resulted in reductions in A1C ranging from 0.25 to 2.6%, depending on the type and duration of diabetes. Multiple encounters and a variety of nutrition therapy interventions were employed. Also reported are improvements in other outcomes, such as lipids, blood pressure, weight management, decreased need for medications, and reduced risk for onset and progression of comorbidities (I)

^†;Grade I: Good evidence supporting statement; Grade II: Fair evidence; Grade III: Limited evidence; Grade IV: Expert opinion; Grade V: Not assignable.

A1C: Hemoglobin A_1c; CVD: Cardiovascular disease.

Data taken from [3,101].

Key issues

• • Nutrition therapy is a proven effective intervention in the management of both Type 1 and Type 2 diabetes. On average, MNT lowers A1C levels by approximately 1–2%, depending on the type of diabetes, duration and level of glycemic control, and similar to glucose-lowering medications.

• • Outcomes from MNT interventions should be monitored at 6 weeks to 3 months and if the person with diabetes has made all the lifestyle changes he/she is willing and able to make and metabolic goals have not been achieved, changes in medication(s) are needed.

• • Just as there is not one medication or insulin regimen that applies to all persons with diabetes, there is not one nutrition intervention that applies to all persons with diabetes. A variety of MNT approaches and eating patterns, along with multiple encounters and ongoing support, have been shown to be effective for improving glycemic control and reducing CVD risk in persons with diabetes.

• • There are no ‘ideal’ percentages of macronutrients – carbohydrate, protein, fat – that apply to all persons with diabetes. Total carbohydrate intake takes precedence over the type of carbohydrate – sugar, starch, low- or high-glycemic index (GI).

• • For persons with Type 2 diabetes, for both glycemic control and weight management, total energy intake is the first priority, not the distribution or type of carbohydrate. The usefulness of the GI concept remains unproven. Two 1-year studies comparing low-GI diet groups to control groups reported no differences in A1C between the groups.

• • For persons with Type 1 diabetes, matching insulin doses to planned carbohydrate intake is beneficial. Persons with both types of diabetes appear to do better when they are more consistent in their carbohydrate intake.

• • The decision to drink or not drink alcoholic beverages must be made with the individual. However, if it is their choice, for the majority of persons with diabetes, alcohol consumption in moderation does not need to be discouraged. For persons using insulin or insulin secretagogues, alcohol should be consumed with food to prevent hypoglycemia.

• • Hopefully, research and technology will continue to improve diabetes management. MNT is important and an effective component of diabetes therapy. As for all Americans, a healthy eating pattern is to be encouraged.

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Nutrition therapy for diabetes: effectiveness, carbohydrates and alcohol

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Activity Evaluation: Where 1 is strongly disagree and 5 is strongly agree

	1	2	3	4	5
1. The activity supported the learning objectives.
2. The material was organized clearly for learning to occur.
3. The content learned from this activity will impact my practice.
4. The activity was presented objectively and free of commercial bias.

1. You are seeing a 50-year-old man with newly diagnosed Type 2 diabetes mellitus, obesity and hyperlipidemia. He wants more information about a healthy diet. What should you consider regarding medical nutrition therapy for diabetes?

• □ A Nutrition therapy can reduce HbA1c by 1% to 2%

• □ B The results of nutrition therapy are not usually manifest until 6 months of treatment

• □ C The benefits of nutrition therapy on HbA1c are limited to early in the disease course

• □ D One-time nutrition advice is as effective as continuous education and counseling

2. What should you tell this patient regarding the consumption of carbohydrates and outcomes important to diabetes?

• □ A Reducing carbohydrate consumption leads to lower LDL cholesterol levels

• □ B The key to weight loss is reduced energy intake and not macronutrient content

• □ C The principal dietary problem in diabetes is excessive consumption of carbohydrates

• □ D Clinical trials consistently demonstrate that low-carbohydrate diets reduce HbA1c levels

3. The patient asks if he should follow the glycemic index (GI) of his diet. What should you consider regarding the GI?

• □ A Foods with a high GI produce a more rapid peak in serum glucose compared with low-GI foods

• □ B Foods with a high GI produce a slightly higher peak serum glucose compared with low-GI foods

• □ C The GI responses in an individual patient are fairly consistent

• □ D The American Diabetes Association (ADA) recommends low-GI diets for all patients

4. What can you tell this patient regarding alcohol consumption and diabetes?

• □ A Regular alcohol consumption increases HbA_1c levels

• □ B Alcohol improves the cardiovascular risk of patients with diabetes primarily through its effects on insulin sensitivity

• □ C All women with diabetes should consume at least 1 alcoholic beverage per day

• □ D All men with diabetes should consume at least 3 alcoholic beverages per day