July 2017 Issue
Diabetes Management & Nutrition Guide: Foods and Eating Patterns for Diabetes Prevention
By Judith C. Thalheimer, RD, LDN
Vol. 19, No. 7, P. 40
Research supports adjustments to overall diet patterns as the best nutritional intervention to reduce diabetes risk, and emerging evidence suggests an emphasis on certain foods within those patterns.
According to the Centers for Disease Control and Prevention, one out of every three American adults has prediabetes; that's 86 million people. Without intervention, 15% to 30% of people with prediabetes will go on to develop type 2 diabetes within five years, but lifestyle changes can help.1 The National Diabetes Prevention Program demonstrated that an intensive lifestyle intervention aimed at achieving 7% weight loss and increasing activity to 150 minutes per week can reduce incidence of type 2 diabetes by 58% over three years.2
While excess body fatness is a recognized risk factor for diabetes (and weight loss is an important way to lower risk), specific diet patterns and foods seem to decrease or increase risk, independent of weight. The latest research suggests that diabetes risk (as well as risk of heart disease and stroke) is largely influenced not by single nutrients but by specific foods and overall diet patterns.3 "We need to think about the foods people are eating, and a pattern that includes not only the standard parts of the plate but also specific foods within that plate that seem to be protective," says Melinda Maryniuk, MEd, RD, CDE, director of care programs for Joslin Innovations at Joslin Diabetes Center in Boston.
Diet Pattern and Prevention
The American Diabetes Association's 2017 Standards of Medical Care in Diabetes clearly state that losing weight is essential for those at high risk of developing type 2 diabetes.2 "A lot of people think you have to cut carbs to prevent diabetes," says Eileen Sturner, MS, RD, CDE, BC-ADM, manager of the Abington Health Diabetes Center in Abington, Pennsylvania, "but what you really need to do is cut pounds. For at-risk individuals, losing just 5% to 10% of starting weight can reduce diabetes risk dramatically," Sturner says. The accepted way to cut pounds is to cut calories.
Maryniuk, who was a member of the Professional Practice Committee responsible for the content of the Standards of Care, says, "The Diabetes Prevention Program research showed that any diet that reduces calories to cause modest weight loss will reduce diabetes risk. The first priority is to lose weight and increase activity, but, at the same time, we need to encourage making the foods in the reduced-calorie diet as healthful and whole as possible."
Poor diet quality may influence weight and metabolic risk independent of calories: Different types of foods have different effects on satiety, glucose-insulin responses, liver fat synthesis, fat-cell function, craving and reward responses in the brain, and the creation of visceral fat. In the same way that physical activity improves metabolic health even in the absence of weight loss, diet quality can improve or worsen things like diabetes risk even without changing caloric intake.3 "Cutting calories can help with weight loss, but many choices leave people missing important nutrients that could be contributing to their overall health," says Marina Chaparro, MPH, RDN, LD, CDE, a spokesperson for the Academy of Nutrition and Dietetics.
It's generally recognized that eating more fruits, vegetables, legumes, nuts/seeds, whole grains, fish/shellfish, dairy products, and vegetable oils, and less refined grains, added sugars, red and processed meats, trans fat, sugar-sweetened beverages (SSBs), and sodium is the best dietary pattern for cardiometabolic health.3-5 But within this pattern, some foods are emerging as particularly helpful (or harmful) in preventing diabetes.
Foods That Raise or Lower Risk
According to the Standards of Care, data suggest that whole grains may help to prevent type 2 diabetes, and higher intakes of nuts, berries, yogurt, coffee, and tea are associated with reduced diabetes risk. Red meats and SSBs are cited as being associated with an increased risk.2
Minimally processed plant foods such as fruits, nonstarchy vegetables, legumes, and nuts/seeds are consistently linked to better cardiometabolic outcomes, including decreased diabetes risk.3
• A 2014 meta-analysis of prospective cohort studies found that higher intake of fruit or green leafy vegetables is associated with a significantly reduced risk of type 2 diabetes.6
• A 2014 systematic review and meta-analysis concluded that eating nuts is associated with lower diabetes risk. Although legumes produce a lower glycemic response, which may protect against diabetes, the authors found a lack of good studies in this area.7
• Whole grains also decrease relative risk of developing diabetes. A systematic review and dose-response meta-analysis of 16 cohort studies by Aune and colleagues in 2013 found that a high intake of whole grains is associated with reduced type 2 diabetes risk, while intake of refined grains isn't. Based on the analysis, the authors recommend at least two servings of whole grains per day.8
Quality is more important than quantity when it comes to carbohydrates. Whole grain content, how intact or processed the grain is, dietary fiber content, and glycemic responses to digestion all determine a carbohydrate's effect on the body.
The bran on intact or partially intact whole grains slows digestion of starch by walling off the starchy endosperm from digestive enzymes. Milled whole grains have a higher glycemic response than intact whole grains because, even though the bran is still present, the starchy endosperm is exposed. Removing the bran and germ to make refined grains (such as white bread, white rice, and many crackers and ready-to-eat cereals) not only removes fiber, minerals, and other nutrients but also results in quicker digestion.3
From a physiological viewpoint, then, starches aren't much different from sugars.3 Like sugars, refined grains and high-starch vegetables like potatoes are rapidly digested and cause similar blood glucose and insulin responses.3 They may stimulate reward/craving areas in the brain, activate the conversion of carbohydrates into fatty acids in the liver, increase uric acid production, and promote visceral adiposity, all of which are detrimental to cardiometabolic health.3 Poor-quality carbohydrates such as sweets, starches, and refined grains also replace more healthful foods (such as fruits and whole grains) in the diet, adding to their detrimental impact on weight and diabetes risk.3
Nearly three in four Americans currently consume too many refined grain products. Consumption was bolstered by the low-fat diet movement, which initiated a proliferation of low-fat or fat-free refined carbohydrate products. People may choose these products, believing they're a more healthful choice than higher-fat foods, without understanding that high intake of refined carbohydrates potentially has equally adverse effects on their cardiometabolic health.3 "I recommend people avoid marketed low-sugar, low-fat, low-carb types of food," Chaparro says. "Low-sugar ice cream is of little benefit to at-risk people. Instead, we need to teach them to fulfill that sweet craving in a more wholesome way."
While they have been studied to different extents, meat, poultry, eggs, fish, and dairy protein sources appear to impact diabetes risk differently.
• In their 2011 meta-analysis, Pan and colleagues determined that red meat consumption, particularly processed red meat, is associated with an increased risk of type 2 diabetes and suggested that substituting one serving of nuts, low-fat dairy, and whole grains per day for one serving of red meat would lower diabetes risk by 16% to 35%.9
• Relatively few studies have looked at poultry as a risk factor for diabetes, and those that do show mixed results. In his expansive 2016 review of evidence, Dariush Mozaffarian, MD, DrPH, concluded that "occasional consumption of poultry and eggs appears relatively neutral for cardiometabolic health, without strong evidence for either risks or benefits." Mozaffarian suggests poultry products be seen as healthful alternatives to harmful foods like processed meats, refined grains, and sugars, but as relatively unhealthful alternatives to beneficial foods.3
• Fish intake appears to have little association with harms or benefits with regard to development of diabetes, although protective associations are seen in Asian populations.3,10
• Mozaffarian calls the cardiometabolic effects of different dairy foods "a major unanswered question of modern nutrition science."3 It's possible that the relationship between dairy and diabetes is determined not by fat content but by food type: In general, milk intake isn't associated with lower incidence of diabetes, but intake of yogurt and fermented dairy products are, as is cheese, despite the latter's high calorie, fat, and saturated fat content.3
Research on fats typically looks at their impact on cardiovascular, not diabetes, risk, and fats' association with diabetes risk is in need of clarification. Recent evidence suggests that the quality of fats consumed in the diet is more important than the total quantity of dietary fat.2 Some researchers point out that source of fat is important, and possibly confounding, in studies looking at total fat intake and health effects. Although some results are controversial, it's important to be aware of and keep an eye on emerging research. Some recent study findings include the following:
• A Mediterranean dietary pattern, which is relatively high in monounsaturated fats, may help prevent type 2 diabetes.2
• High vegetable fat intake may decrease type 2 diabetes risk in females.11
• Intake of high-fat, but not low-fat, dairy products is associated with a decrease in type 2 diabetes risk.12 Mozaffarian concludes that findings suggest butter is, at worst, neutral for diabetes risk.3
• EPA+DHA seems to provide neither harm nor benefits with regard to diabetes development. The omega-3 fatty acid ALA (alpha-linolenic acid) may be associated with modestly lower risk.10
Since fat is calorically dense (9 kcal/g as opposed to 4 kcal/g for protein or carbohydrate), it's often the focus of weight loss diets.
What people drink also can have an important impact on their health, including diabetes risk.
• SSBs have been well documented to increase weight. Excess body fatness is a risk factor for diabetes, but SSBs also are associated with increased incidence of diabetes in their own right.3
• One hundred percent fruit juices have sugar content similar to SSBs but are linked to relatively smaller long-term weight gain. Short-term trials showed no appreciable effect of 100% fruit juice on glucose-insulin homeostasis, but fruit juices or drinks with added sugars are associated with diabetes in longitudinal studies. Mozaffarian posits that things like dietary fiber, vitamins, and phytochemicals found in natural fruit juice may at least partly offset the harms of the high sugar content and suggests the evidence indicates up to one serving of 100% fruit juice per day appears reasonable.3
• Both coffee (caffeinated and decaffeinated) and tea are associated with lower risk of diabetes, and are specifically referenced in the 2017 Standards of Care.2,3
• There's strong evidence that moderate alcohol use is associated with lower diabetes risk across diverse populations, but people who don't currently drink alcohol shouldn't be encouraged to do so, and drinkers should limit themselves to up to two drinks per day for men and one to 1.5 for women.3
Putting It Into Practice
Based on the latest research, a dietary pattern to lower diabetes risk would limit red and processed meats, refined grains, sweets and SSBs, and emphasize plant foods like whole grains, nuts, fruits, and leafy green vegetables. Evidence supports including coffee, tea, yogurt, vegetable fats, and possibly cheese.
Working with dietary pattern instead of focusing on individual nutrients or "superfoods" (or vilifying particular food groups) allows greater flexibility for clients. It lets them choose foods they like at times that are convenient to them. Discussing ways they can add a fruit or nonstarchy vegetable to their regular meals or snacks, easy ways to prepare fish, or how delicious nuts and seeds are tossed into a variety of dishes is likely to be better received than a list of off-limit foods. "It's not just about eating less of certain foods," Maryniuk says. "It's equally important to eat more of certain other foods—with the overall emphasis being on choosing high-quality, nutrient-dense foods."
Given the health advantages of plant foods like leafy greens and whole grains and their association with reduced diabetes risk, encouraging a diet pattern that includes plenty of these foods is a sound investment in diabetes risk reduction. "More vegetarian-style diets are beneficial for everybody," Chaparro says. "Incorporating a Meatless Monday-style approach can remove some meats and add in plant foods that have been shown to decrease diabetes risk."
Begin by discussing areas where small changes would make the biggest impact. "Snacking is an area typically wide open for improvement," Chaparro says. "I suggest people get creative with their snacking, choosing wholesome things like fruit and honey-almond butter instead of packaged refined-carbohydrate snacks. Think outside the box, instead of out of a box." Chaparro emphasizes the importance of details. "Make sure clients leave with a plan," she says. "Be as specific as possible, even breaking down the type of snack they're going to have. It's not enough to suggest they have more veggies at breakfast. Dig deeper. Which do they like? If they like tomatoes, give specific suggestions for adding tomatoes to breakfast, and hand them a recipe. Registered dietitians can give clients the resources they need to enable them to reach their goals."
"Permanent behavior change is difficult to achieve," Sturner says, "but people with prediabetes or high risk of developing type 2 diabetes are often intrinsically motivated to change. Dietitians can empower at-risk people to take control."
— Judith C. Thalheimer, RD, LDN, speaks and writes about all things nutrition-related from her home near Philadelphia.
1. Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Division of Diabetes Translation. National diabetes statistics report, 2014. https://www.cdc.gov/diabetes/pubs/statsreport14/national-diabetes-report-web.pdf. Published 2014.
2. American Diabetes Association. 5. Prevention or delay of type 2 diabetes. Diabetes Care. 2017;40(Suppl 1):S44-S47.
3. Mozaffarian D. Dietary and policy priorities for cardiovascular disease, diabetes, and obesity: a comprehensive review. Circulation. 2016;133(2):187-225.
4. US Department of Health & Human Services, Office of Disease Prevention and Health Promotion. Scientific Report of the 2015 Dietary Guidelines Advisory Committee: Part D. Chapter 2: dietary patterns, foods and nutrients, and health outcomes. https://health.gov/dietaryguidelines/2015-scientific-report/07-chapter-2/. Updated May 30, 2017.
5. The American Heart Association's diet and lifestyle recommendations. American Heart Association website. http://www.heart.org/HEARTORG/HealthyLiving/HealthyEating/Nutrition/The-American-Heart-Associations-Diet-and-Lifestyle-Recommendations_UCM_305855_Article.jsp#.WRNbd7GZO1s. Updated March 27, 2017.
6. Li M, Fan Y, Zhang X, Hou W, Tang Z. Fruit and vegetable intake and risk of type 2 diabetes mellitus: meta-analysis of prospective cohort studies. BMJ Open. 2014;4(11):e005497.
7. Afshin A, Micha R, Khatibzadeh S, Mozaffarian D. Consumption of nuts and legumes and risk of incident ischemic heart disease, stroke, and diabetes: a systematic review and meta-analysis. Am J Clin Nutr. 2014;100(1):278-288.
8. Aune D, Norat T, Romundstad P, Vatten LJ. Whole grain and refined grain consumption and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies. Eur J Epidemiol. 2013;28(11):845-858.
9. Pan A, Sun Q, Bernstein AM, et al. Red meat consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis. Am J Clin Nutr. 2011;94(4):1088-1096.
10. Wu JH, Micha R, Imamura F, et al. Omega-3 fatty acids and incident type 2 diabetes: a systematic review and meta-analysis. Br J Nutr. 2012;107(Suppl 2):S214-S227.
11. Alhazmi A, Stojanovski E, McEvoy M, Garg ML. Macronutrient intakes and development of type 2 diabetes: a systematic review and meta-analysis of cohort studies. J Am Coll Nutr. 2012;31(4):243-258.12. Ericson U, Hellstrand S, Brunkwall L, et al. Food sources of fat may clarify the inconsistent role of dietary fat intake for incidence of type 2 diabetes. Am J Clin Nutr. 2015;101(5):1065-1080.