Nutrition in Patients With Diabetes

Diabetes is a chronic illness that requires a holistic approach to care to prevent both acute and long-term complications. Nutritional management for diabetic patients has been evolving for more than 100 years as the pathophysiological basis of complications due to diabetes becomes more explicit.

Medical nutrition therapy (MNT) is extremely important for diabetic patients and prediabetic patients so that adequate glycemic control can be achieved. The American Diabetes Association (ADA) recommends individualized MNT, preferably provided by a registered dietitian, for all people with type 1 or type 2 diabetes.[1] Nutrition counseling should be sensitive to the culture, socioeconomic demographic, and personal needs of the patient, including how motivated the patient is to change their dietary and lifestyle habits.[2] MNT delivered by a registered dietitian is associated with hemoglobin A1c (HbA1c) decreases of 0.3–1% for people with type 1 diabetes and 0.5–2% for people with type 2 diabetes.[1]

There is growing evidence of the effectiveness of online diabetes self-management programs.[3] In an internet-based diabetes prevention program (DPP) pilot study, 187 participants diagnosed with prediabetes enrolled in Prevent, a group-based lifestyle intervention that integrates a private online social network, weekly lessons, health coaching, and a wireless scale and pedometer. After a core 16-week intensive lifestyle change intervention, 155 participants continued with a maintenance intervention. Those participants who completed only the initial 16 week intervention lost an average of 4.2% (SD 0.8) and reduced HbA1c by mean 0.43% (SD 0.08) after 2 years. Those who completed the maintenance intervention lost mean 4.3% (SD 0.8) and reduced HbA1c by 0.46% (SD 0.08) after 2 years. For both groups, neither 2-year weight loss nor HbA1c results were significantly different from 1-year results.[4, 5]

Medical nutrition therapy for diabetics can be divided into (1) dietary interventions and (2) physical activity. Lifestyle and dietary modifications form the cornerstone of therapy in type 2 diabetic patients (insulin resistance). In type 1 diabetic patients, who have an insulin deficiency, a balance between insulin and nutrition needs to be obtained for optimal glycemic control.[6]

Nutrition therapy for diabetic patients can be further divided into prevention and continual management of glycemic control. The goals of nutrition therapy are as follows:

• Primary prevention – Identification of the population at high risk (body mass index [BMI] >25) for obesity or prediabetic state, and implementation of diet and lifestyle changes to achieve and maintain weight goals to prevent or delay type 2 diabetes

• Secondary prevention - Utilization of therapeutic modalities to attain glycemic, blood pressure, and lipid goals to prevent or delay the complications of diabetes

• Tertiary prevention - Nutrition as a tool to manage the macrovascular and microvascular complications of diabetes, and to prevent or delay increased morbidity and mortality

Food groups include macronutrients and micronutrients. As there is no single ideal dietary distribution of calories among carbohydrates, fats, and proteins for people with diabetes; macronutrient distribution should be individualized while keeping total calorie and metabolic goals in mind. Reduction in fat (saturated fats, trans fats, cholesterol) intake in diabetic patients is aimed at decreasing cardiovascular disease risk by reducing plasma cholesterol and low-density lipoprotein (LDL) cholesterol levels.[7] The ADA guidelines find a variety of eating patterns are acceptable for the management of type 2 diabetes and prediabetes including Mediterranean, DASH, and plant-based diets.[1]

Low-carbohydrate and low-fat diets used to achieve initial weight loss are effective for the short term (approximately 1 y) and need monitoring with a lipid profile and renal function tests. Low-carbohydrate diets (20-120 g/d) carry the additional benefit of a favorable lipid profile as compared with low-fat diets. Low-carbohydrate diets have also been noted to decrease fasting plasma glucose values by about 21-28 mg/dL.[8, 9]

The results of a systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes found that low carbohydrate diets (LCD) with energy percentage of carbohydrates below 45% had a greater effect on glycemic control in the short term than did higher carbohydrate diets (HCD). In addition, among LCDs in the analysis, the greater the restriction, the greater the glucose lowering. However, in the long term, the glucose-lowering effect of LCD and HCD was similar. In addition, LCD and HCD had similar effects on body weight, LDL cholesterol, and quality of life.[10]

In another study in which subjects (N=322) were randomized to 1 of 3 diets (Mediterranean, restricted-calorie; low-fat, restricted-calorie; low-carbohydrate, non–restricted-calorie) found that at 2-year follow-up, the 36 diabetic subjects assigned to the Mediterranean diet had more favorable fasting plasma glucose and insulin levels compared with those assigned to the low-fat diet.[11]

Plant-based diets have been shown to have a positive effect in both the prevention and treatment of type 2 diabetes in several clinical trials. Plant-based diets are a particularly effective dietary approach for weight loss. In the BROAD study, a 6-month, whole-food, plant-based diet with no energy restrictions showed a mean BMI reduction of 4.4 kg/m2 compared with usual care (0.4 kg/m2), in overweight or obese subjects.[12] A 2014 meta-analysis found significantly improved blood sugar control in type 2 diabetes for individuals on a plant-based diet. The benefit of omitting meat, cheese, and eggs was as much as 0.7 points in some studies, and averaged about 0.4 points overall.[13]

For patients who are on insulin therapy or oral hypoglycemics, being on a restrictive diet requires adjustment of dosage to prevent hypoglycemia.

Carbohydrate choices in diabetes are as follows:

• Carbohydrates are necessary for energy, some vitamins, fiber, and dietary palatability, and as a major regulator of postprandial glucose levels

• Evidence is inconclusive for an ideal amount of carbohydrate intake for people with diabetes. For good health, carbohydrate intake from vegetables, fruits, whole grains, legumes, and dairy products are advised over intake from other carbohydrate sources, especially those that contain added fats, sugars, or sodium.[14]

• Type of carbohydrates (ie, starch, amylose, amylopectin) consumed reflects on postprandial glucose values

• Consumption of low–glycemic index foods can result in a drop of 0.4% in hemoglobin A1c (HbA1c) compared with high–glycemic index foods[15] ; limitations to this diet choice include bloating and a restrictive diet

• The ADA finds the use of nonnutritive sweeteners have the potential to reduce overall calorie and carbohydrate intake if substituted for caloric sweeteners without compensation by intake of additional calories from other food sources.[1]

The ADA found evidence inconclusive for an ideal amount of total fat intake for people with diabetes and recommended individualized goals. Fat quality is thought to be far more important than quantity.[1, 14] Dietary fat recommendations in diabetes are as follows:

• Saturated fat, cholesterol, and trans fat is the same as that recommended for the general population.

• Monounsaturated fatty acid (MUFA) may benefit glycemic control and CVD risk factors and is an effective alternative to a lower-fat, higher-carbohydrate eating

• As recommended for the general population, servings of fish at least two times (two servings) per week as a form of omega-3 fatty acids, because of their beneficial effects on lipoproteins, prevention of heart disease, and association with positive health outcomes[14]

• Plant sterols intake to block intestinal absorption of cholesterol and lower total plasma LDL cholesterol percentage, if intake is around 2 g/d[16, 14]

A good quality, high-protein diet is recommended. This measure can aid in achieving weight loss and blood glucose level control.[8] However, protein appears to increase insulin response without increasing plasma glucose concentrations. Therefore, carbohydrate sources high in protein should not be used to treat or prevent hypoglycemia in individuals with type 2 diabetes.[1]

In addition to the macronutrients, micronutrients are an important component of a balanced diet. Uncontrolled diabetic patients are usually micronutrient deficient because of poor dietary choices. Physicians should encourage meeting daily needs from a healthy, balanced diet rather than from supplementation with multivitamins.[17] If this cannot be achieved, then a daily multivitamin is acceptable. Zinc, copper, and chromium have been studied but do not play any role in achieving tight glycemic control.[18]

Much interest has been sparked in the role of antioxidants and diabetes, as diabetes has been noted to be a state of oxidative stress. Flaxseed has been shown in experiments to decrease inflammatory markers in type 2 diabetic patients, but there are no specific and reliable recommendations.[19] Vitamin E in combination with other antioxidants has the tendency to do more harm than good if taken over prolonged periods.[17] Patients should always be asked about their use of herbal supplements for treatment of their type 2 diabetes, as herbal supplements can interact with other medications and produce unexpected adverse effects. To date, evidence of herbal supplements aiding diabetes management is insufficient.[20]

Adults with diabetes who choose to indulge in alcohol should be cautioned about the risk of nocturnal hypoglycemia if it is consumed without food at night.[21] The ADA recommends that men should limit their intake to two drinks per day, while for women one drink per day is suggested.[1] One alcohol beverage is defined as a 12-oz serving of beer, a 5-oz serving of wine, or a 1.5-oz serving of distilled spirits. Complete abstinence from alcohol should be advised to people who have severe peripheral neuropathy and hypertriglyceridemia.

All adults should decrease the amount of time spent in daily sedentary behavior. Prolonged sitting should be interrupted every 30 min for blood glucose benefits, particularly in adults with type 2 diabetes.[1]

Children and adolescents with diabetes or prediabetes should engage in 60 minutes or more each day of moderate- or vigorous-intensity aerobic activity, with vigorous muscle-strengthening and bone-strengthening activities at least 3 days a week. Adults should engage in 150 minutes or more of moderate-to-vigorous intensity physical activity per week, spread over at least 3 days per week, with no more than 2 consecutive days without activity. In addition, adults should engage in 2–3 sessions each week of resistance exercise on nonconsecutive days.[1]

The National Heart, Blood and Lung Institute, using the National Health and Nutrition Examination Survey (NHANES) data, defines persons being overweight as having a BMI of 25-29.9 kg/m2 and as being obese as having a BMI greater than 30 kg/m2.[22]  For type 2 diabetic patients with a BMI greater than 35 kg/m2, greater benefit has been noted if they undergo bariatric surgery compared with continual medical therapy with regard to glucose control and weight loss.[23] Studies have shown that a high BMI with an increased waist circumference (an indicator of visceral fat) is a predictor of the development of type 2 diabetes and cardiovascular disease. In both short- and long-term studies evaluating weight loss and its resultant effect on a drop in hemoglobin A1c, however, results have not been consistent.

Yoga has been suggested as an alternative for severe diabetic patients who may be unable to participate in strenuous activity. Malhotra et al undertook a 20-patient study in Delhi, India and concluded that yoga has a beneficial effect on glucose control, as well as promoting weight loss.[24] The ADA guidelines recommend flexibility training and balance training 2–3 times/week for older adults with diabetes. Yoga and tai chi are acceptable practices to increase flexibility, muscular strength, and balance.[1]

For type 1 diabetic patients with macrovascular or microvascular complications, an individualized exercise regimen is warranted as strenuous exercise can result in complications. If patients have active proliferative diabetic retinopathy, they should be advised to refrain from strenuous exercise or Valsalva maneuvers, as these can precipitate vitreous hemorrhage. Patients with microalbuminuria (>20 mg/min albumin excretion) or frank proteinuria (>200 mg/min protein excretion) should not engage in high-intensity physical activity.

In type 1 diabetic patients, the risk for developing hypoglycemia exists during, immediately after, or up to 24 hours after engaging in physical activity, which mandates adjustment in the therapeutic regimen. To prevent hypoglycemia, patients usually reduce their insulin dose before exercise, but this strategy can only be used when exercise is planned in advance. An additional drawback is that patients try to keep their blood glucose higher before exercise in order to maintain proper glycemic profile during and after exercise. They do that by increasing consumption of carbohydrates before and during exercise, which results in increased energy intake and consequent weight gain.[25]

Key precautions for exercise programs in diabetes are as follows:

• Evaluation of the patient prior to embarking on an exercise regimen, with a thorough physical examination and careful medical tests, with documentation of grade of retinopathy, nephropathy, and neuropathy (both peripheral and autonomic)

• Baseline resting ECG to check for any ST and T segment abnormalities; additional radionuclide stress testing may be warranted

• Doppler ultrasound and ankle brachial index if evidence of peripheral arterial disease is present

• Should a patient with sensitive feet undertake exercise, ulceration and fractures may result; weight-bearing exercises should be limited; swimming is the ideal exercise in this case

• A warm-up and cool-down session of 5-10 minutes must always be undertaken

• Use of silica gel or air insoles, in addition to polyester or blend (cotton-polyester) socks, to prevent blisters and maintain circulation

• Footwear should be appropriate at all times

• Patient examination of the feet prior to and after physical exercise

• A diabetic bracelet should be worn and steps should be taken to ensure its visibility

• An average of 17 oz of fluids should be consumed at least 2 hours prior to the start of exercise in order to maintain adequate hydration

Managing diabetes requires a multidisciplinary approach, and nutrition and physical exercise are two significant facets to help reduce the global burden of the diabetes epidemic. To ensure successful outcomes, physicians, patients, and dietitians need to work together. Studies have shown that one-on-one consultations with a qualified registered dietitian improve patient adherence to prescribed diabetic diets.

The cornerstones of therapy for type 2 diabetic patients are diet and lifestyle modifications. For type 1 diabetic patients, the goal of optimal glycemic control can be achieved with a balance between insulin and nutrition needs.