New Research Supports the Positive Role of Flaxseed in the Reduction of Diabetes

By Kelley Fitzpatrick

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Diabetes is characterized by hyperglycemia due to defects in insulin metabolism. Chronic hyperglycemia results in organ damage, particularly to the eyes, kidneys, heart and vasculature. Type 1 diabetes is due to an absolute deficiency of insulin secretion, whereas type 2 diabetes is caused by a combination of insulin resistance and inadequate compensatory insulin secretion. Type 2 diabetes is the far more common form of the disease, accounting for 90-95% of cases.1

The number of adults with diabetes is rising rapidly and is now estimated to be 8.3% of the global population, or 387 million people.2 In Canada, diabetes prevalence is projected to reach 3.2 million people in 2016.3 In the United States, 29.1 million people or 9.3% of the population have diabetes, resulting in an estimated expenditure of $245 billion in 2012.4

Three key compounds in flaxseed appear provide a protective and perhaps even a therapeutic effect on diabetes risk factors:

  • Lignans: flaxseed is the richest source of plant lignans, particularly secoisolariciresinol diglucoside (SDG), which is converted by intestinal bacteria to the mammalian lignans secoisolariciresinol (SECO), enterodiol and enterolactone. The approximate SDG content in flaxseed is 375 mg/100 g.
  • Omega-3 fatty acids: flaxseed is the richest plant source of the essential fatty acid a-linolenic acid (ALA). Approximately 55-57% of the fatty acids in flaxseed are ALA.
  • Dietary fibre: flaxseed is a rich source of dietary fibre, including both insoluble and soluble fibre. Flaxseed provides 4 g of fibre in a 2 tablespoon serving.

The results of human clinical trials investigating the effects of flaxseed on glucose control and insulin sensitivity are inconsistent. Key papers have been published since June, 2017 which provide more clarity as to the relationship of flaxseed on diabetes. The most impressive of this work is a recent paper detailing the results of a systematic review on randomized controlled trials assessing the effects of flaxseed consumption on glycemic control5. PubMed, Medline via Ovid, SCOPUS, EMBASE, and ISI Web of Sciences databases were searched up to November 2016. Clinical trials in which flaxseed or its products were administered as an intervention were included. The outcomes were fasting blood glucose, insulin concentration, insulin resistance (HOMA-IR), insulin sensitivity (QUIKI), and hemoglobin A1c (HbA1c). A total of 25 randomized clinical trials (30 treatment arms) were included. Meta-analysis suggested a significant association between flaxseed supplementation and a reduction in blood glucose (weighted mean difference [WMD], -2.94 mg/dL; 95%CI, -5.31 to - 0.56; P = 0.015), insulin levels (WMD – 7.32 pmol/L; 95%CI, -11.66 to -2.97; P = 0.001), and HOMA-IR index (WMD, -0.49; 95%CI,: -0.78 to - 0.20; P = 0.001) and an increase in QUIKI index (WMD, 0.019; 95%CI, 0.008-0.031; P = 0.001). No significant effect on HbA1c (WMD, -0.045%; 95%CI, -0.16 to - 0.07; P = 0.468) was found.

In subgroup analysis, a significant reduction in blood glucose, insulin, and HOMA-IR and a significant increase in QUIKI were found only in studies using whole flaxseed but not flaxseed oil and lignan extract. Furthermore, a significant reduction was observed in insulin levels and insulin sensitivity indexes only in the subset of trials lasting ≥12 weeks. The meta-analysis concluded whole flaxseed, but not flaxseed oil and lignan extract, has significant effects on improving glycemic control. 

Another study assessed the mechanisms involved in the attenuation of postprandial glycemic and insulinemic responses associated with soluble dietary fibre (SDF) consumption6. The effect of SDF, including soluble flaxseed gum on in vitro amylolysis and maltose transport was studied. A human clinical trial was also conducted to investigate the effect of SDF consumption on postprandial glycemic and insulinemic responses and gastric emptying. Participants (n = 15) at risk for type II diabetes consumed maltose syrup- and starch-based pudding treatments supplemented with 11.4 g of flaxseed gum (SDF), at a concentration to match three times the apparent viscosity (18.54 mPa s at 60 s-1). The presence of SDF delayed in vitro amylolysis and attenuated blood glucose and plasma insulin peak concentrations 1 h incremental area under the curve values relative to the controls. The postprandial attenuations were related to the ability flaxseed SDF to modify and increase digesta viscosity, perhaps through the delay of gastric emptying, as a delay of amylolysis and sugar transport under simulated upper intestinal conditions did not seem to have a substantial effect.

Previous research has found that daily flaxseed consumption appears to reduce glucose and insulin and improve HOMA-IR when incorporated into the habitual diet in prediabetics, overweight or obese men and postmenopausal women7. Flaxseed fibre and lignan have a potential protective effects on normal subjects against the occurrence of hyperlipidemia, hyperglycemia and oxidative stress8. Further work is recommended with regard to the effects of flaxseed oil on glycemic control as several studies reported on flaxresearch.com have found negative correlations between intake of alpha-linolenic acid and the lowering of diabetic symptoms9.

References

  1. American Diabetes Association. Diabetes Care 2014;37 Suppl 1:S81-90.
  2. International Diabetes Federation. 2014. Diabetes Atlas: Key Findings 2014. http://www.idf.org/diabetesatlas/update-2014.
  3. Mathers CD, et al. PLoS Med 2006;3:e442.
  4. Centers for Disease Control and Prevention. 2014. National Diabetes Statistics Report, 2014. http://www.cdc.gov/diabetes/pubs/statsreport14/national-diabetes-report-web.pdf.
  5. Mohammadi-Sartang M, Sohrabi Z, Barati-Boldaji R, Raeisi-Dehkordi H, Mazloom Z. Flaxseed supplementation on glucose control and insulin sensitivity: a systematic review and meta-analysis of 25 randomized, placebo-controlled trials. Nutr Rev. 2017 Dec 8. doi: 10.1093/nutrit/nux052.
  6. Repin N, Kay BA, Cui SW Wright AJ, et al. Food Funct. 2017. Investigation of mechanisms involved in postprandial glycemia and insulinemia attenuation with dietary fibre consumption. Jun 5. doi: 10.1039/c7fo00331e.
  7. Hutchins AM, Brown BD, Cunnane SC, Domitrovich SG, Adams ER, Bobowiec CE. Daily flaxseed consumption improves glycemic control in obese men and women with pre-diabetes: a randomized study. Nutr Res. 2013;33(5):367–375.
  8. Demmers A, Korthout H, van Etten-Jamaludin FS, et al. Effects of medicinal food plants on impaired glucose tolerance: A systematic review of randomized controlled trials. Diabetes Res Clin Pract. 2017 Jun 13;131:91-106. doi: 10.1016/j.diabres.2017.05.024
  9. Soleimani Z, Hashemdokht F, Bahmani F, et al. J Diabetes Complications. 2017. Clinical and metabolic response to flaxseed oil omega-3 fatty acids supplementation in patients with diabetic foot ulcer: A randomized, double-blind, placebo-controlled trial. Sep;31(9):1394-1400. doi: 10.1016/j.jdiacomp.2017.06.010