Nutrition and Diabetes: A Closer Look at Current Research

by Katelyn Castro

No one ever said understanding the components of a healthy diet would be simple. The connections between nutrition and disease continue to grow and evolve as scientific research emerges. Consider the most recent publication of the 2015 Dietary Guidelines for Americans (DGA). All of the past and present dietary guidelines may share some common themes, but every five years they are updated after an extensive review of the current scientific literature.

Similar to the process of the DGA, the American Diabetes Association (ADA) systematically reviews the latest research on diabetes care and releases new guidelines including specific nutrition recommendations. As the science on the role of nutrition in the pathophysiology of diabetes advances, the ADA’s most recent report, Standards of Medical Care in Diabetes—2016 aims to put the current research in perspective. Before getting into the recommendations, understanding the basic science of diabetes is crucial.

The Science Behind Diabetes

Diabetes Mellitus, more commonly known as diabetes, makes up a large group of endocrine disorders (See “Is There a Fourth Type of Diabetes?” and “Debunking 6 Myths About Diabetes“). But, for the purpose of this article, we will focus on type 1 and type 2 diabetes. While these two types of diabetes differ in etiology, they share a common characteristic: high blood glucose (hyperglycemia), caused by a defect in insulin production, insulin action, or both.

Insulin is an important hormone, produced and secreted by the beta cells in the pancreas. One of its major functions is to keep blood glucose levels within a healthy range, by working closely with another hormone, glucagon. For people without diabetes, fasting blood glucose typically ranges from 70 to 100 mg/dL.

After eating a meal, glucose and amino acid levels in the blood rise, signaling the pancreas to release insulin. Insulin allows glucose to be transported out of the blood and into liver, muscle, and fat cells for immediate energy or for stored energy as glycogen and fat.

On the other hand, after exercise or between meals, glucose and insulin levels drop, causing another hormone, glucagon to be released. Glucagon signals the liver to convert glycogen back into to glucose to raise blood glucose levels. If glycogen stores are exhausted, glucagon can also signal the liver to make new glucose from amino acids, usually from muscle protein. By working together, insulin and glucagon keep blood glucose levels within a relatively narrow range, while making sure our brain, muscles, and other organs get the energy they need to function properly.

Unfortunately, this is not the case for people with diabetes. Type 1 diabetes is an autoimmune disease where the beta cells in the pancreas are destroyed so the pancreas cannot produce adequate insulin.

In type 2 diabetes, the body cannot use insulin effectively because muscle, fat, and liver cells become resistant. At first, the pancreas tries to overcome insulin resistance by producing extra insulin to help glucose get into cells. But eventually, the pancreas can’t keep up with the high need for insulin and loses the ability to produce it. While type 2 diabetes can be reversed in the early stages, late-stage type 2 diabetes must be handled similarly to type 1 diabetes: with insulin medication. Balancing insulin doses effectively with diet is the key to managing abnormal blood glucose levels, the cause of many of the serious diabetes-related health concerns.

For instance, if people with diabetes take too much insulin, blood glucose levels can drop extremely low, causing seizures, loss of consciousness, and even death. On the other hand, if people with diabetes don’t take enough insulin when eating, blood glucose can rise very high, causing headaches, blurred vision, and fatigue. Also, when extremely high blood glucose levels are not treated quickly, diabetic ketoacidosis can occur and cause shortness of breath, vomiting, or a coma.

Untreated hyperglycemia can also contribute to many long-term complications, such as cardiovascular disease, kidney damage, nerve damage (neuropathy), and blindness. Several studies have found that long-term hyperglycemia accelerates the formation of advanced glycation end products (AGEs). A recent study suggests that AGEs are mediators of many diabetes complications because they speed up oxidative damage and increase inflammation, which are linked to many of the health conditions listed above. Given these serious health consequences, management of abnormal blood glucose levels is one of the primary goals of diabetes care.

Nutrition and Diabetes Management: The Consensus from Current Research

According to the Standards of Medical Care in Diabetes—2016, nutrition therapy plays an integral role in overall diabetes management. Within this report, the American Diabetes Association conducted a systematic review of all available research on diabetes nutrition research, using a strict grading system according to the level of evidence:

A: Clear evidence from a well-conducted randomized controlled trial or Evidence-Based Medicine at the University of Oxford

B: Supportive evidence was from well-conducted cohort studies

C: Supportive evidence was from poorly controlled or uncontrolled studies or conflicting evidence with weight of evidence supporting recommendation

E: Evidence was from expert consensus or clinical experience

Together, the ADA states that the recommendations in the report aim to help people with diabetes reach individualized glycemic, blood pressure, and lipid goals; achieve a healthy body weight; and delay and prevent complications of diabetes. The following paragraphs are a review of some of the recommendations in the 2016 report.

Carbohydrates remained a hot topic, consistent with earlier ADA reports. The ADA recognizes that the amount of carbohydrates and available insulin are important factors influencing glycemic response (blood glucose control). The report recommends that certain people with type 2 diabetes who are not taking insulin may benefit most from education that emphasizes healthy food choices and portion control (B rating).

In contrast, carbohydrate counting or estimation to determine insulin at mealtimes is recommended for people with type 1 and 2 diabetes who use fixed insulin therapy to improve glycemic control (A rating). These recommendations are consistent with previous research, finding that carbohydrates cause an immediate and significant increase in blood glucose, while protein has a much smaller effect, and fat has the least impact. In addition, studies have found that adding protein or fat to a carbohydrate meal slows the blood glucose response and lowers blood glucose levels, when compared to the response of a carbohydrate-only meal.

The new report also emphasizes the quality of carbohydrates more than the quantity of carbohydrates. While previous reports have listed a minimum amount of carbohydrates and specific recommendations for grams of fiber, the 2016 ADA recommendations focus on identifying healthy sources of carbohydrates. To avoid displacing nutrient-dense foods, carbohydrates from vegetables, fruits, whole grains, legumes and dairy are recommended, especially high-fiber and low glycemic load foods (B rating). More specifically, the 2016 report recommends that all people with diabetes avoid sugar-sweetened beverages to control weight and lower risk of CVD and fatty liver (B rating), which is stricter than previously reports that only recommended limiting sugar-sweetened beverages. Similar to carbohydrates, fat quality is highlighted rather than quantity in the report. Specifically, omega-3 fatty acids are recommended to prevent or treat cardiovascular disease.

While evidence on the ideal amount of carbohydrates, fat, or protein remains inconclusive (E rating), a healthy eating pattern with calorie reduction continues to be recommended for overweight adults with type 2 diabetes to support modest weight loss (A rating). In addition, the ADA states that a Mediterranean diet, low in carbohydrates and rich in monounsaturated fatty acids, is considered as effective as the traditionally recommended low-fat, high-carbohydrate diet for glycemic control and cardiovascular improvements (B rating). Although some research studies advocate for carbohydrate restriction as the primary approach in diabetes management, as outlined in this critical review, the ADA is not completely on board. To meet the ADA evidence-based criteria for nutrition recommendations, long-term randomized controlled trials are needed to address concerns about the efficacy and safety of a restricted carbohydrate diet for diabetes management.

The report also addresses restrictions on alcohol intake (C rating), which are the same as those recommended for the general population. In addition, recommendations for sodium restriction are consistent with previous reports and that of the general population (less than 2,300 mg/day), although a stricter restriction is recommended for people who have both diabetes and hypertension (B rating). Despite this comprehensive review of current evidence from diabetes nutrition research, the ADA makes an important point: the evidence is only one component of decision-making.

The Role of the RD and the Individual

After understanding the research supporting various nutrition recommendations, registered dietitians are responsible for working with people with diabetes to translate the population-based research into practical terms for individuals. As the ADA recognizes in the report, the research does not identify a one-size-fits-all eating pattern for people with diabetes. Instead, people with diabetes should follow an eating plan most appropriate for them by taking into account personal and cultural preferences, health literacy and numeracy, and willingness and ability to make behavior changes. This individualized approach can help people with diabetes maintain the pleasure of eating, while also meeting personal health goals through education and counseling on evidence-based recommendations.

For example, consider nutrition recommendations for a 40-year-old woman who is part of a traditional Asian family and has type 2 diabetes. While replacing white rice with brown rice in her diet may be an unrealistic goal because of her family’s cultural values, choosing fresh fruit instead of fried ice-cream for dessert may be more manageable for her. Now, consider recommendations for a 16-year-old teen recently diagnosed with type 2 diabetes. Teaching him about portion control and how to identify high- and low-carbohydrate foods may be simpler and more feasible than explaining carbohydrate counting initially.

Nutrition, Diabetes, and the Big Picture

Taking a larger socio-ecological perspective on the role nutrition in diabetes is equally important as scaling down recommendations for individuals with diabetes. While nutrition plays a critical role in management of diabetes, many other factors also impact health and wellbeing: physical activity, smoking status, social support, stress, sleep, and mental health.

Just as no single eating pattern has been found to be most effective for all people with diabetes, no one component of diabetes management should be underscored without addressing other important sectors of health. By taking the current research on diabetes nutrition into perspective, people with diabetes can find an eating pattern that is both consistent with research and in line with their personal values and health goals.

Katelyn Castro is a first-year student in the DI/MS Nutrition Program at the Friedman School. She is passionate about teaching nutrition to kids and has spent the past two summers working with kids with type 1 diabetes at the Barton Center.

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