Fiber can improve glycemic control in patients who have T2DM
Diabetes mellitus is on the rise in the United States. In 2014, approximately 9.3% of the U.S. population was living with diabetes. This number had increased from 8.3% in 2011.1,2 Unfortunately, 8.1 million (27.8%) of these cases remain undiagnosed. Type 2 diabetes mellitus (T2DM) accounts for approximately 90% to 95% of those with diabetes.3 Diabetes is currently the most common cause of kidney failure, non-traumatic lower-limb amputations, and new cases of blindness in the US. In 2010, diabetes was listed as the seventh leading cause of death in the US. Patients with diabetes are at a 2 to 4 times increased risk of stroke and death from heart disease as compared to those without diabetes.2
Genetics play a significant role in the development of T2DM. The risk increases tremendously for patients who have a first-degree relative with T2DM. Concordance of T2DM equals approximately 70% to 90% in identical twins.4
Detrimental lifestyle habits also represent a major risk factor for the development of T2DM. According to the American Diabetes Association (ADA), obesity is the most significant risk factor for DM.5 Physical inactivity also increases risk for obesity and development of T2DM. In the Nurses’ Health Study, each 2 hours per day spent watching television was associated with a 23% increased risk of obesity and a 14% increased risk of T2DM. In contrast, each 1 hour per day spent walking was associated with a 34% decreased risk of both obesity and diabetes.5
Race and ethnicity can also affect risk for T2DM. Native American, African-American, Hispanic, Asian-American, and Pacific Islander ethnicities are at increased risk of T2DM.6
Other medical conditions also influence risk for the development of diabetes. Previously established cardiovascular disease (CVD), hypertension (HTN), and dyslipidemia place patients at greater risk of developing metabolic abnormalities, leading to T2DM.6
Current screening protocols recommend testing for T2DM in asymptomatic adult patients of any age who are overweight (BMI ≥ 25 kg/m2), and have at least one additional risk factor for diabetes.6
For those patients with a healthy weight and without additional risk factors, screening should begin at age 45. Testing should be repeated every year if results are elevated, or every 3 years if results are normal.6
Appropriate screening tests include glycosylated hemoglobin (HbA1c), fasting plasma glucose (FPG), or the 2-h 75-g oral glucose tolerance test (OGTT).6
Early Diabetes Management
Lifestyle modifications (LSM’s) should be the initial intervention in diabetes management. A low-fat, heart-healthy diet should be followed, and carbohydrate intake must be monitored. Reducing postprandial glucose response is the main goal of diet therapy.7 Most dietary carbohydrates should come from vegetables, fruits, whole grains, legumes and dairy sources.6 Lower-calorie diets consisting of fruits, vegetables, whole grains, nuts, and yogurt are negatively correlated with weight gain, encouraging weight reduction and improved glucose metabolism.5 Physical activity, with a goal of at least 30 minutes per day for at least 5 days per week, complements a healthy diet and provides for better overall glucose regulation. Modest weight loss is recommended in overweight or obese diabetic patients. Weight loss of approximately 5% to 10% aids in better glycemic control and in lowering blood pressure and lipid levels.6
Current Recommendations for Dietary Fiber
Dietary fiber (DF) refers to non-digestible plant carbohydrates in foods, which are usually a mix of polysaccharides that are integral components of the plant cell wall (or the intercellular structure of plants) that cannot be broken down by the human digestive tract.8 High-fiber carbohydrates, such as whole grains, vegetables, fruits and fiber supplements, are recommended in patients with diabetes to improve glycemic control.7 The Academy of Nutrition and Dietetics (formerly the American Dietetic Association) currently recommends 25 to 30 grams of fiber per day for the general population.
However, most Americans currently consume an average of only 10 to 15 grams of fiber daily.8,9 The American Heart Association recommends that at least half of an individual’s daily grain intake come from whole grain sources.9 The ADA currently recommends that patients with diabetes follow these guidelines as well, and consume 25 to 30 grams of fiber daily.6
In clinical studies, glucose levels are inversely proportional to dietary fiber intake in diabetic patients. One clinical study compared two groups of patients with T2DM. The intervention group consumed 50 grams of fiber per day; the control group consumed 24 grams. The results of the six-week study showed that the participants in the intervention group maintained consistently lower glucose, insulin, and lipid levels compared to those of the control group.10 A 2013 meta-analysis also reviewed the effects of fiber-rich diets or fiber supplements on overall glycemic control. The difference in fiber intake between the intervention and control groups ranged from 3.0 grams to 22.5 grams of fiber per day.7 These results suggest an average reduction of 0.55% in HbA1C levels and an average reduction of 10mg/dL of fasting plasma glucose (FPG) in those with increased dietary fiber intake.7
Types and Sources of Fiber
Dietary fiber has traditionally been categorized into soluble and insoluble fiber, based on its solubility in water. Most whole foods contain both types of fiber.10
Insoluble fiber acts as a natural laxative, and it is the mainstay of treatment for constipation and hemorrhoids.8,10 Insoluble fiber increases the rate of gastric emptying, forms bulk, and aids in fecal excretion through the intestinal tract. Sources of insoluble fiber include wheat bran, brown rice, carrots, and fruit peels, such as apples, grapes, and blueberries.8,10
Soluble fiber, on the other hand, draws water into the gastrointestinal tract to form a viscous-gel. This substance prolongs digestion, causing decreased absorption of macronutrients, such as glucose, triglycerides, and cholesterol in the gut.8,10-11 Sources of soluble fiber include oat bran, barley bran, psyllium, pectin, dried beans and peas, and the pulp portion of many fruits.8,10
As stated earlier, most Americans only consume an average of half of the recommended daily amount of fiber through their diet. Various over-the-counter pharmacologic fiber supplements are available to achieve the daily recommended amount of fiber intake. These supplements are available in formulations that may contain wheat dextrin, methylcellulose, psyllium husk, inulin, or calcium polycarbophil. Dosage forms include caplets, chewable tablets, capsules, wafers, and dissolvable powders.9
Mechanisms of Glucose Regulation by Fiber
The mechanisms by which DF improves glucose control are multifaceted. As previously mentioned,8,10-11 the viscous gel-forming property of water-soluble fiber slows gastric emptying and decreases absorption of glucose from the digestive tract. This process significantly decreases the post-prandial glucose response,7 a major contributor to HbA1c levels, and an independent risk factor for CVD in patients with diabetes.7 Reducing the post-prandial glucose response results in lower HbA1c levels and decreases risk of CVD.
Several studies have indicated that total dietary fiber intake was inversely associated with markers of insulin resistance.11 In particular, insoluble fiber has been associated with improved insulin sensitivity and decreased diabetes risk.11
With the increase of bulk in the gut and decreased intestinal absorption, a high water-soluble fiber diet increases satiety and achieves meaningful weight reduction.11
The benefits of high-fiber intake in the prevention and management of obesity, DM, CVD, and colon cancer are well established. Emerging research is now suggesting that DF may influence the immune system by altering biomarkers of inflammation, such as C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), and by regulating intestinal flora. DF may affect cognition, memory and mood, due to its role in regulating systemic inflammation, depression, and anxiety. While these additional benefits of DF appear promising, inconsistent findings have resulted from these clinical studies. This may reflect a difference in fiber type, dosage, and the study population, so further interventional trials are needed.12
Possible Interactions with Prescription Medications
Fiber supplements can cause decreased absorption and efficacy of certain prescription medications, such as tricyclic antidepressants (TCAs), carbamazepine, and lithium.10 While fiber supplements have been associated with improved glucose regulation, the mixture of fiber supplements with diabetic medications, such as metformin and oral sulfonylureas, can also decrease the absorption of these drugs and worsen DM control. Care must be taken to avoid taking fiber supplements along with prescription medications.10 Patients should allow 2 to 3 hours between the ingestion of a fiber supplements and the ingestion of their other medications to prevent decreased absorption of those other medications.10
The prognosis for T2DM largely depends upon tight glycemic regulation, increased exercise and weight loss, the effective treatment of comorbidities, and the prevention and treatment of diabetic complications.13 Microvascular disease, such as diabetic retinopathy and diabetic nephropathy, is reduced in patients with tight glycemic control. It is also reduced with the use of antihypertensive therapy in hypertensive patients.13 CVD is the most common cause of death in patients with T2DM.4,13 Yet CVD is not diminished with glycemic control. Cardiovascular complications are reduced with antihypertensive treatment, not T2DM agents.13
Successful treatment of T2DM in overweight and obese patients remains a major challenge. Goals are aimed at weight loss, exercise enforcement, glycemic control, antihypertensive therapy, and treatment of dyslipidemia. With successful weight reduction and maintenance of healthy blood pressure and lipid levels, the prognosis for T2DM greatly improves.6 Once diagnosed with T2DM, patients should be educated on the importance of improving their lifestyle habits. Dietary changes should be addressed, particularly decreasing caloric intake, monitoring carbohydrates, and increasing daily consumption of dietary fiber.
1. Centers for Disease Control and Prevention. National Diabetes Statistics Report, 2014: Estimates of Diabetes and Its Burden in the United States. https://www.cdc.gov/diabetes/pubs/statsreport14/national-diabetes-report-web.pdf
2. Centers for Disease Control and Prevention. National diabetes fact sheet, 2011. https://www.cdc.gov/diabetes/pubs/pdf/ndfs_2011.pdf
3. The American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care. 2014;37(S1):S81-S90.
4. Powers, AC. Diabetes mellitus. In: Longo DL, Fauci AS, Kasper DL. Harrison’s Principles of Internal Medicine. 18th ed. New York, NY: McGraw-Hill Education; 2012:2968-3003.
5. Hill JO, Galloway JM, Goley A, Marrero DG, Miners R, Montgomery B et al. Scientific statement: socio-ecological determinants of prediabetes and type 2 diabetes. Diabetes Care. 2013;36.
6. The American Diabetes Association. Standards of medical care in diabetes-2014. Diabetes Care. 2014;37(S1):S14-S63.
7. Silva FM, Kramer CK, De Almeida JC, Steemburgo T, Gross Jl, Azevedo MJ. Fiber intake and glycemic control in patients with type 2 diabetes mellitus: a systematic review with meta-analysis of randomized controlled trials. Nutrition Reviews. 2013;71(12):790-801.
8. The American Dietetic Association. Position of the American Dietetic Association: health implications of dietary fiber. J Am Diet Assoc. 2008;108(10):1716-1731.
9. Terrie, YC. Fiber supplements: health benefits & side effects. Pharmacy Times. http://www.pharmacytimes.com/publications/issue/2014/July2014/Fiber-Supplements-Health-Benefits-and-Side-Effects.
10. University of Maryland Medical Center. Fiber. http://umm.edu/health/medical/altmed/supplement/fiber.
11. Weickert MO, Pfeiffer AFH. Recent advances in nutritional sciences: metabolic effects of dietary fiber consumption and prevention of diabetes. J. Nutr. March 2008;138(3):439-442.
12. Kaczmarczyk MM, Miller MJ, Freund GG. The health benefits of dietary fiber: beyond the usual suspects of type 2 diabetes, cardiovascular disease and colon cancer. Metabolism. 2012; 61(8):1058-1066.
13. Masharani, U. Diabetes mellitus & hypoglycemia. In: Papadakis MA, Mcphee SJ, Rabow MW, eds. CURRENT Medical Diagnosis & Treatment 2014. 53rd ed. San Francisco, CA: McGraw-Hill Education; 2014: 1150-1201.