Medical Nutrition Therapy for the Prevention and Treatment of Diabetes and Its Complications

The number of persons at risk for and with diabetes is increasing rapidly around the world. The World Health Organization (WHO) estimates that more than 180 million persons around the world have diabetes, and that this number will more than double by 2030 (1). The problem is especially serious in Asia. There are now 90 million people with diabetes in India, China, Pakistan and Japan; the WHO predicts that in less than a decade, 60% of all persons with diabetes will be in Asia (2). Some organizations, including the International Diabetes Federation, have estimated even higher worldwide prevalence of diabetes (3).

The Canadian Diabetes Association estimates that at least 2.2 million Canadians have diabetes, with many more cases remaining undiagnosed. By the end of the decade, over three million Canadians could have diabetes. An aging population, a rise in obesity and sedentary lifestyles, and immigration from high-risk groups (people of Hispanic, Asian, South Asian or African descent) are the factors contributing to the increasing number of diagnoses. Moreover, The Aboriginal population is 3-5 times as likely to be diagnosed with type 2 diabetes as compared to the rest of the Canadian population. Children, too, are being increasingly diagnosed; American data suggests that children of high-risk population groups have a 1 in 3 chance of being diagnosed with type 2 diabetes in their lifetime.

Also of great concern are those individuals who have been diagnosed with pre-diabetes, which includes impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG). These individuals are at high risk for type 2 diabetes and/or cardiovascular disease if lifestyle prevention strategies are not implemented and followed.

Type 1 diabetes accounts for approximately 5% to 10% of all known cases of diabetes. The etiology of type 1 diabetes involves a genetic predisposition and an autoimmune destruction of the pancreatic beta cells that produce insulin. This results in a nearly absolute insulin deficiency, making persons dependent on insulin for life. Although type 1 diabetes can occur at any age, even in the eighth and ninth decade, the majority of individuals who develop this type of diabetes do so before age 30.

Ninety to 95% of cases of diabetes are type 2 diabetes. Both genetic and environmental factors contribute to its development. Obesity, particularly intra-abdominal obesity, sedentary lifestyle, aging and a high-fat, high-calorie diet have been identified as environmental factors.

The key to the prevention of diabetes and its complications is early diagnosis and intervention. Type 2 diabetes is a progressive disease caused by both insulin resistance and insulin deficiency. Insulin resistance (decreased cell sensitivity or responsiveness to insulin) is evidenced by an elevation of postprandial glucose values. As insulin deficiency (beta cell failure) becomes more prominent, fasting glucose levels increase due to an increase in hepatic glucose production, especially in the early morning. Evidence shows that the best way to slow the progression of diabetes and its complications is excellent glucose control.

To achieve and maintain glucose goals as diabetes progresses, therapy needs may change. Treatment begins with aggressive lifestyle interventions including plans for healthy eating and physical activity. However, as beta cell failure continues, for many individuals, insulin and/or other medication(s) need to be combined with nutrition therapy. It is important for people managing diabetes to understand that this is not because the “diet” or glucose-lowering medications fail, but because the beta cells of the pancreas are no longer able to produce the insulin needed to maintain adequate glucose control.

Diabetes is also associated with hypertension and a dyslipidemia characterized by increased triglycerides, decreased high-density lipoprotein (HDL) cholesterol and increased small, dense low-density lipoprotein (LDL) cholesterol. Control of hyperglycemia, hypertension and dyslipidemia has been shown to reduce complications of diabetes such as cardiovascular disease, microvascular complications and neuropathy. Canadian Diabetes Association, Clinical Practice Guidelines are listed in Table 1 (5).

Table 1. Canadian Diabetes Association, Clinical Practice Guidelines

Glycemic control
A1C
Fasting/preprandial plasma glucose
2-hr postprandial plasma glucose
Therapeutic goal:
<7.0%
4.0–7.0 mmol/lL
5.0-10.0 mmol/L
Lipids
LDL cholesterol
Triglycerides
Total cholesterol/HDL cholesterol ratio
Therapeutic goal:
<2.0 mmol/L
<1.5 mmol/L
<4.0 mmol/L
Blood pressureTherapeutic goal:
<130/80 mm Hg

*Source: Canadian Diabetes Association, 2003
±Treatment goals and strategies should be tailored to each patient on an individual basis with consideration given to possible risk factors.

Nutrition Recommendations and Interventions for Diabetes

The Canadian Diabetes Association clinical practice guidelines recognize the importance of nutrition therapy as an integral part of diabetes management. An individualized nutrition therapy plan can improve glycemic control as well as additional clinical and metabolic results. The goal of nutrition therapy is to improve or maintain quality of life, nutritional status and physiological health. Nutrition therapy also aims to prevent and/or treat the complication of diabetes and its comorbidities. Working with a Registered Dietitian (RD) on an individual or group basis is recommended for people with diabetes, and individualized eating plans should be reevaluated on a regular basis (5).

Nutrition Therapy for Overweight and Obesity

Along with an elevated body mass index (BMI), waist circumference is a proxy measure of intra-abdominal obesity. A waist circumference >40 inches (102 cm) in men and >35 inches (88 cm) in women indicates increased diabetes risk (5). For Asian populations, lower waist circumference cut points [>35 inches (88 cm) in men and >31 inches (78 cm) in women] are used.

Lifestyle modification is usually the first option for treating overweight and obesity to prevent or delay diabetes. The goal is to produce modest weight loss of 5% to 10% of baseline weight via dietary changes and increased moderate physical activity, resulting in a decrease of 500 to 1000 calories per day (5). Meal replacements, weight loss medications and/or bariatric surgery may be appropriate for some individuals with obesity. With ongoing support, the health benefits and much of the weight loss can be maintained, thus reducing risk for developing type 2 diabetes (6).

Nutrition Therapy for Pre-Diabetes

Clinical trials strongly support the potential for moderate weight loss to reduce the risk of type 2 diabetes (7-9). Both moderate intensity physical activity and vigorous exercise improve insulin sensitivity, independent of weight loss. A minimum of 150 minutes per week of moderate intensity physical activity, distributed over at least 3 days and with no more than 2 consecutive days without physical activity, is recommended (5). Other studies provide evidence for increased intake of whole grains and fiber. Both are associated with improved insulin sensitivity, independent of body weight (10-16).

Nutrition Therapy for Type 1 and Type 2 Diabetes

Clinical trials and outcome studies demonstrate that nutrition therapy provided by RDs as nutrition therapy alone or in combination with diabetes self-management training is associated with a decrease in A1C of ~1% in patients with type 1 diabetes and, depending on the duration, in type 2 diabetes of 1%–2% (17, 18). These outcomes are similar to those achieved with oral glucose-lowering medications. Interventions included carbohydrate counting; reduced calorie, fat or carbohydrate intakes; basic nutrition education about healthy food choices; and matching insulin doses to planned carbohydrate intake. The effectiveness of nutrition therapy on A1C is known within 6 weeks to 3 months. At this point it needs to be determined whether the medical goals are being met, or if changes to medication, food and/or exercise are needed to achieve glycemic goals.

Research data suggests that reducing saturated fat to 7%–10% of daily energy intake and dietary cholesterol to 200–300 mg/day lowers LDL cholesterol on average by 0.5–0.65 mmol/l; outcomes from nutrition therapy on lipids should be evaluated at 3 to 6 months (19). Additionally, meta-analysis and expert committees support the role of lifestyle modifications in the treatment of hypertension (20).

Weight loss is also recommended for all overweight or obese adults who have type 2 diabetes, with lifestyle modifications including diet and physical activity as the preferred treatment approach. Drug therapy for obesity and/or surgery to achieve weight loss may be appropriate for some individuals (5).

  • Nutrition Interventions for Type 1 Diabetes. The first priority of nutrition therapy for type 1 diabetes is to integrate an insulin regimen into the lifestyle of the person requiring insulin. Those on exogenous insulin regimens or insulin pumps should adjust their mealtime rapid-acting insulin dose based on planned carbohydrate intake. The Dose Adjusted for Normal Eating (DAFNE) trial reported improvements in A1C of ~1% when individuals were taught to adjust their insulin dose based on planned carbohydrate intake (21). For individuals on fixed insulin doses, carbohydrate intake on a day-to-day basis should be kept consistent in regard to both time and amount.
  • Nutrition Interventions for Type 2 Diabetes. Nutrition therapy progresses from preventing overweight and obesity, to improving insulin resistance and preventing or delaying the onset of diabetes, to improving metabolic control when diabetes is diagnosed. Teaching which foods are carbohydrate, average carbohydrate portion sizes and how many carbohydrate servings to select at meals (and snacks, if desired) are the first steps in food and meal planning. Limiting saturated and trans fats, encouraging physical activity and using blood glucose monitoring to adjust food, eating patterns and medications are also important components of successful nutrition therapy for type 2 diabetes. Follow-up with an RD can provide the problem-solving techniques, encouragement and support that lifestyle changes require.
  • Nutrition Interventions for the Complications of Diabetes. Because cardiovascular disease risk factors are similar in persons with and without diabetes, benefits observed in nutrition studies in the general population most likely apply to persons with diabetes as well. In normotensive and hypertensive persons, a controlled sodium intake (<2,400 mg/day), modest amounts of weight loss and a diet high in fruits, vegetables and low-fat dairy products can lower blood pressure. Although not without controversy, reduction of protein intake to 0.8–1.0 g/kg body weight per day and to 0.8 g/kg body weight per day in the later stages of chronic kidney failure may improve measures of renal function, such as urine albumin excretion and glomerular filtration rate (22).

Nutrient Intake and Diabetes

The optimal mix of macronutrients for people with diabetes has not been defined. Macronutrient intake should be individualized and is primarily based on the individual’s willingness and ability to make food and eating changes. The Dietary Reference Intakes recommendations suggesting that adults should consume 45%–60% of total energy from carbohydrate, 20%–35% from fat and 10%–35% from protein to minimize the risk of chronic diseases can be used as a starting point (23).

  • Carbohydrate. It is important to include foods containing carbohydrate (e.g., fruits, vegetables, whole grains, legumes, low-fat milk) in a healthy diet. The amount of carbohydrate ingested and available insulin are the primary determinants of postprandial glucose response. Therefore, using the Beyond the Basics Choice System or monitoring carbohydrate intake by carbohydrate counting remain the primary strategies for achieving glycemic control. Foods with added sugars can be substituted for other carbohydrate-containing foods in moderation or, if added, adequately covered with insulin or other glucose-lowering medication. Of course, nutrient-dense foods are recommended and should be given priority in meal planning. And, as for the general population, people with diabetes are encouraged to eat a variety of fibre-containing foods.

    The type of carbohydrate, however, also affects blood glucose levels. Studies have shown that replacing high glycemic index (GI) foods with low GI foods reduces the acute postprandial glucose response. In type 1 diabetes, increasing intake of low GI foods helps to reduce the number of hypoglycemic incidents, while in type 2 diabetes, increased intake of low GI foods helps to optimize glycemic control. Decisions to increase intake of low GI foods should be based on the individual’s preferences and interest in making changes (5).
  • Fats and Cholesterol. Because the cardiovascular risk for people with diabetes is considered to be equivalent to that of non-diabetic individuals with pre-existing cardiovascular disease, it is recommended that saturated fat intake should be limited to <10% of total energy intake and dietary cholesterol should be less than <200 mg/ day. Trans fat should be avoided as much as possible (24). Recent research has shown that polyunsaturated fats have effects similar to monounsaturated fats on plasma lipid concentrations; therefore, saturated fats can be replaced with either poly- or monounsaturated fats (25).
  • Protein. A number of small, short-term studies in persons with diabetes have shown that glucose produced from ingested protein does not increase circulating glucose levels, but does produce acute insulin responses. Other small, short-term studies suggest that diets containing more than 20% of total energy intake from protein may reduce appetite and increase satiety. However, long-term effects, including risk for renal degeneration, are unknown and preliminary data suggest that it may be difficult for free-living persons to follow these diets long term. The Canadian Diabetes Association maintains that usual protein intake of 15-20% of total energy does not need to be modified for people with diabetes (5, 6).
  • Alcohol. Moderate amounts of alcohol ingested with food have minimal, if any, acute effect on glucose and insulin levels. However, because alcohol intake promotes hepatic glucose uptake, resulting in a drop in blood glucose, if alcohol is consumed with little or no food by individuals using insulin or insulin secretagogues, hypoglycemia can result. Although the data do not support recommending alcohol to people with or at risk for diabetes, preliminary data suggest a U- or J-shaped association between moderate alcohol intake (1 to 3 drinks [15-45 g alcohol] per day) and decreased risk of diabetes and coronary heart disease (26). If adults with diabetes choose to drink alcohol, daily intake should be limited to 1 drink per day or less for women and 2 drinks per day or less for men and can be considered an occasional substitution into the regular meal plan. While the type of alcohol-containing beverage does not appear to make a difference, the calories associated with both alcohol and mixers must be accounted for in the meal plan.
  • Micronutrients. There is no clear evidence of benefit from vitamin or mineral supplementation in people with diabetes who do not have underlying deficiencies; an exception is folate for women of child-bearing age for the prevention of birth defects. Routine supplementation with antioxidants is not advised, as more research is needed to promote understanding of mechanisms and actions of antioxidants in relation to disease (6, 27).

Summary

The role of lifestyle (healthy diet, appropriate food choices and physical activity) is crucial in both prevention and treatment of diabetes. Nutrition therapy for people at risk for and with diabetes should be individualized. The individual’s food and eating habits, metabolic profile, treatment goals and desired outcomes are factors that need to be considered when planning and implementing primary interventions such as carbohydrate control, limiting intake of saturated and trans fats and encouraging physical activity. Monitoring metabolic parameters, including glucose, A1C, lipids, blood pressure, body weight and renal function, is essential to assess the need for changes in therapy and to ensure successful outcomes.

References:

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  2. World Health Organization. Preventing Chronic Diseases: A Vital Investment. Geneva, Switzerland: WHO Press, 2005.
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Original author of American article: Marion J. Franz, MS, RD, CDE.
  • Credited as a contributor in final copy due to substantial edits on the part of advisory committee, s per Ceil Maher’s comments.
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