Viscous Fiber Supplements in Diabetes Control: Results from a Systematic Review and Meta-analysis of Randomized Controlled Trials

Viscous Fiber Supplements in Diabetes Control: Results from a Systematic Review and Meta-analysis of Randomized Controlled Trials

By Heather Nelson Cortes, PhD and Kevin C Maki, PhD

According to the recent 2019 American Diabetes Association (ADA) Standards of Medical Care in Diabetes, people with diabetes should increase their intake of viscous fiber from sources such as oats, legumes, and citrus to help regulate blood glucose levels and lower risk of cardiovascular disease1. Viscous fibers are described as such because they increase viscosity in the human gut, thereby reducing the rate at which carbohydrates are digested and the glucose molecules from them absorbed.  These effects occur because the viscous solution impedes the ability of digestive enzymes to reach starch molecules and slows the rate at which glucose molecules reach the brush border in the intestinal lumen, where absorption can occur.  The result is flattening of the postprandial glycemic and insulinemic responses.  While these acute effects are well established, the longer-term impacts of viscous fibers on glycemic control markers are not well known2.


In a systematic review and meta-analysis, Jovanovski2 investigated the effect of viscous dietary fiber supplementation on markers of glycemic control in people with type 2 diabetes (T2D).  A comprehensive literature search on MEDLINE, Embase, and Cochrane Central Register of Controlled Trials through June 15, 2018 identified 2,716 potential RCTs.  After reviewing the studies based on the inclusion/exclusion criteria, 27 studies (n = 1,394) were identified for the review and meta-analysis.  Inclusion criteria were: ≥3 weeks in duration, studied viscous fiber supplementation (β-glucan, guar gum, konjac, psyllium, pectin, xanthan gum, locust bean gum, alginate, agar) compared to an appropriate control (i.e., fiber-free supplement or one containing insoluble fiber, background diet, or placebo), and included at least one glycemic measurement (glycated hemoglobin [HbA1c], fasting glucose, fasting insulin, homeostatic model assessment of insulin resistance [HOMA-IR], or fructosamine).


The median age of subjects was 60 years (range 48-67) and they had a median body mass index of 27 kg/m2 (range 26-32 kg/m2).  The median dose of viscous fibers in the studies was 13.1 g/day (range 2.55-21.0 g/day) and the median study duration was 8 weeks (range 3-52 weeks).


Compared to control groups, inclusion of viscous fiber in the diet was associated with significant reductions in HbA1c, fasting blood glucose and HOMA- IR. 


  • HbA1c: mean difference (MD) -0.58% 95% confidence interval (CI) -0.88%, -0.28%; p = 0.0002;
  • Fasting blood glucose: MD -14.8 mg/dL 95% CI -23.8, -5.59; p = 0.001
  • HOMA-IR: MD -1.89 95% CI -3.45, -0.33; p = 0.02.


There were no differences between viscous fiber groups and controls for fasting insulin (MD -2.53 µU/mL 95% CI -5.41, 0.35; p = 0.08) or fructosamine (MD -0.12 mmol/L 95% CI -0.39, 0.14; p = 0.37).  Only 2 studies reported fructosamine, so this finding should be interpreted with caution.  There was no evidence of a significant dose-response effect.  Results for HbA1c, fasting glucose, fasting insulin, and HOMA-IR were graded moderate for certainty of evidence, while fructosamine was graded low.


Comment.  Viscous fiber intake, through consumption of food sources such as legumes, whole fruits (e.g., apples and pears) and whole grain oats and barley, as well as dietary supplementation with products such as psyllium (e.g., Metamucil®), methylcellulose (e.g., Citrucel®) or konjac (e.g., Lipozene®), appears to have several benefits regarding cardiometabolic health.  For those with T2D, this meta-analysis shows evidence to support favorable effects on glycemic control and insulin sensitivity.  More research is needed to establish more clearly whether all viscous fibers enhance insulin sensitivity, or whether this property is limited to those with certain characteristics, such colonic fermentability or content of specific bioactive compounds3,4.  Evidence from other sources also shows that viscous fiber lowers the circulating cholesterol level, likely by trapping cholesterol and bile acids, thus preventing their absorption/reabsorption3.  In addition, viscous fibers appear to play a role in appetite regulation, enhancing satiety after meal5.


The meta-analysis by Jovanovski and colleagues shows that inclusion of viscous fiber in the diet produces clinically meaningful improvements in glycemic control for patients with T2D.  Based on this, as well as evidence for other benefits (cholesterol lowering and enhanced satiety), inclusion of viscous fiber from foods and/or supplements should be considered an important component of the management plan for patients with T2D.



  1. American Diabetes Association. 10. Cardiovascular Disease and Risk Management: Standards of Medical Care in Diabetes—2019. Diabetes Care. 2019;42(Supplement 1): S103-S123.


  1. Jovanovski E, Khayyat R,  Zurbau A,  et al. Should viscous fiber supplements be considered in diabetes control? Results from a systematic review and meta-analysis of randomized controlled trials. Diabetes Care. 2019 Jan; doi:10.2337 [Epub ahead of print].


  1. Weickert MO, Pfeiffer AFH. Impact of dietary fiber consumption on insulin resistance and the prevention of type 2 diabetes. J Nutr. 2018;148:7-12.


  1. Kärkkäninen O, Lankinen MA, Vitale M, et al. Diets rich in whole grains increase betainized compounds associated with glucose metabolism. Am J Clin Nutr. 2018;108:971-979.


  1. Rebello CJ, Chu YF, Johnson WD, et al. The role of meal viscosity and oat ß–glucan characteristics in human appetite control: a randomized crossover trial. Nutr J. 2014;13:49.



Photo by Sara Dubler

Results From a Systematic Review and Network Meta-Analysis Suggest that Lower Systolic Blood Pressure Targets Are More Effective for Reducing Risks for Cardiovascular Disease Events and Mortality

Reducing Risks for Cardiovascular Disease Events

Results From a Systematic Review and Network Meta-Analysis Suggest that Lower Systolic Blood Pressure Targets Are More Effective for Reducing Risks for Cardiovascular Disease Events and Mortality

Clinical trials have documented that lowering blood pressure reduces cardiovascular disease (CVD) and early death.1 However, the optimal target(s) for reduction of systolic blood pressure (SBP) are uncertain.1-4 Scientists from Tulane University School of Public Health and Tropical Medicine and the School of Medicine, along with scientists from the Medical College of Soochow University, China, conducted a systematic review and meta-analysis to assess the association of mean achieved SBP levels with the risk of CVD and all-cause mortality in adults with hypertension treated with antihypertensive therapy.5 From a MEDLINE and EMBASE search of articles through December 2015, Dr. Joshua Bundy and his colleagues identified 42 clinical trials of 144,200 patients that met their pre-defined criteria of random allocation to an antihypertensive medication, control, or treatment target that reported a difference in mean achieved SBP of 5 mm Hg or more between the groups compared.  The results showed that there was a linear association between mean achieved SBP and risks of CVD and mortality.  An achieved SBP of 120-124 mm Hg had the lowest risk.  Subjects in this lowest category had a hazard ratio (HR) of 0.82 (95% confidence interval [CI] 0.67-0.97) compared to subjects with even slightly higher SBP of 125-129 mm Hg, and this continued linearly through all of the 5 mm SBP cutpoints up to the comparison with the highest level of SBP ≥160 mm Hg, for which the HR for SBP of 120-124 mm Hg was 0.36 (95% CI 0.26-0.51). Similarly, subjects with an achieved SBP of 120-124 mm Hg had a HR for all-cause mortality of 0.74 (95% CI 0.57-0.97) compared with subjects in the 125-129 mm Hg category, and the benefit to all-cause mortality continued to as much as 0.47 (95% CI 0.32-0.67) when compared to subjects with SBP ≥160 mm Hg.


The 2003 7th Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of Blood Pressure recommended SBP goals of <130 mm Hg for patients with type 2 diabetes or chronic kidney disease and <140 mm Hg for individuals at least 60 years of age.1  The 8th Report of the Joint Committee released in 2014, raised these treatment targets to <140 and <150 mm Hg, respectively.2  The investigators of the Systolic Blood Pressure Intervention Trial (SPRINT) examined the association with CVD and all-cause mortality risks of the more intensive treatment goal (SBP <120 mm Hg) compared to <140 mm Hg among men and women with hypertension and at high CVD risk (but without diabetes or stroke).3  The mean achieved SBP was 121.5 mm Hg in the intensive-treatment group and 134.6 mmHg in the standard-treatment group. During a median follow-up of 3.3 years, a 25% reduction in the primary composite outcome of CVD events (HR, 0.75; 95% CI, 0.64-0.89; P < .001) and a 27% reduction in all-cause mortality (HR, 0.73; 95% CI, 0.60-0.90; P = .003) were observed.  However, some were concerned that those results were not necessarily generalizable for a variety of reasons.

Current guidelines provide inconsistent recommendations regarding the optimal SBP target, particularly in older adults.  Earlier this year, the American College of Physicians and the American Academy of Family Physicians released their joint guideline with evidence-based  recommendations on the benefits and harms of higher (<150 mm Hg) versus lower (≤140 mm Hg) SBP targets for hypertension in adults at least 60 years of age.4  They reported that mortality, incidence of stroke, and cardiac events were all reduced with the lower SBP target, but that treating to a lower target did not further reduce mortality, quality of life, or functional status in the target patient population.  They also reported increased withdrawals due to adverse events, as well as increased cough, hypotension, and risk of syncope with treating to the lower vs. higher SBP targets.  A report from the panel appointed to the Eighth Joint National Committee, recommended a SBP treatment target of 150 mm Hg for adults aged 60 years or older.2

On the other hand, in an analysis6 of data from 2636 SPRINT participants who were ≥75 years of age (mean age, 79.9 years; 37.9% women), at a median follow-up of 3.1 years, there were significantly lower rates of the primary composite outcome, HR = 0.66 (95%CI, 0.51-0.85) and all-cause mortality HR = 0.67 (95%CI, 0.49-0.91). The overall rate of serious adverse events was not different between treatment groups (48.4% in the intensive treatment group vs 48.3% in the standard ≥treatment group.

The multiple sets of hypertension guidelines and recommendations create confusion about the most appropriate blood pressure targets for patients with hypertension.  The results from the meta-analysis by Bundy et al.5 support the interpretation of the SPRINT investigators that a lower target is associated with reduced CVD and mortality risk.  Results from the subgroup analysis from SPRINT of elderly participants with a mean age of nearly 80 years suggest that a lower SBP target may produce benefits without unacceptable adverse effects even at advanced ages.  These findings suggest that reassessment of the body of evidence for the currently recommended SBP targets may be warranted.



  1. Chobanian AV, Bakris GL, Black HR, et al. Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. National Heart, Lung, and Blood Institute; National High Blood Pressure Education Program Coordinating Committee. Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Hypertension. 2003;42:1206-1252.


  1. James PA, Oparil S, Carter BL, et al. 2014 Evidence-based guideline for the management of high blood pressure in adults: report from the panel members appointed to the Eighth Joint National Committee (JNC 8). JAMA. 2014;311:507-520.


  1. Wright JT, Jr., Williamson JD, Whelton PK, et al.; SPRINT Research Group. A randomized trial of intensive versus standardized blood-pressure control. N Engl J Med. 2015;373:2103-2116.


  1. Qaseem A, Wilt Tj, Rich R, et al.; Clinical Guidelines Committee of the American College of Physicians and the Commission on Health of the Public and Science of the American Academy of Family Physicians. Pharmacologic treatment of hypertension in adults aged 60 years or older to higher versus lower blood pressure targets: A clinical practice guidelines from the American College of Physicians and the American Academy of Family Physicians. Ann Intern Med. 2017;166:430-437.


  1. Bundy JD, Li C, Stuchlik P, Bu X, et al. Systolic blood pressure reduction and risk of cardiovascular disease and mortality: a systematic review and network meta-analysis. JAMA Cardiol. 2017; May 31, 2017 [Epub ahead of print].


  1. Williamson JD; Supiano MA, Applegate WB et al. Intensive vs Standard Blood Pressure Control and Cardiovascular Disease Outcomes in Adults Aged ≥75 Years. A Randomized Clinical Trial. JAMA. 2016;315:2673-2682.



Reducing Risks for Cardiovascular Disease Events