Flaxseed, derived from the flax plant, was originally used primarily as a laxative, but recent research has found other potential benefits. Flaxseed contains large amounts of alpha-linolenic acid, an omega-3 fatty acid. Omega-3 fatty acids help reduce inflammation and can lower cholesterol levels. Flaxseed is also the dietary source highest in lignans. Lignans act as phytoestrogens, weak plant sources of estrogen. Flaxseed also contains fiber, which can lower cholesterol and blood glucose. However, clinical studies on the effects of flaxseed and flaxseed oil on lowering blood sugar levels have had mixed results.
Flaxseed contains both soluble and insoluble fiber, with slightly more soluble than insoluble fiber. Soluble fiber may help lower blood sugar levels by slowing the absorption of glucose through the small intestine. Slowing glucose absorption stabilizes blood sugars and prevents the rapid increases that can occur after eating. Lignans in flaxseed may also have some benefit on blood sugar levels.
Few recent studies have been done on the effects of flaxseed on blood sugar levels. A Canadian study published in the “British Journal of Nutrition” in March 1993 reported that healthy subjects who consumed 50 g of flaxseed in meals for four weeks experienced a 27 percent decline in blood sugar levels after eating. A Chinese study reported in the November 2007 “PloS One” found that ingestion of a flaxseed-derived dose of 360 mg lignan for 12 weeks modestly lowered hemoglobin A1C levels, which show the trend of blood glucose levels over a three-month period. Fasting blood sugar and insulin levels were not improved in this study.
In a Canadian study reported in the 2008 “Journal of Oleo Science,” 10 g of flaxseed oil capsules given for three months failed to show any improvement in fasting glucose levels, insulin levels or Hgb A1C levels. MayoClinic.com reports that in one case series, rather than lowering blood sugar, flaxseed produced hyperglycemia, or high blood sugar effects.
Taking omega-3 fatty acids may increase your fasting blood-glucose levels, which may necessitate an increase in anti-diabetic medications, the University of Maryland Medical Center warns. Flaxseed can also interfere with the absorption of medications and could change the dose of diabetes medications needed to control blood sugar levels. The effects of phytoestrogens in flaxseed on hormone-dependent tumors such as breast, uterine or prostate cancer are not well established. Do not take flaxseed if you have or are at high risk of developing hormone-dependent tumors. Because the effects of flaxseed on blood glucose are not well established, do not take flaxseed to lower blood sugar if you have diabetes without talking with your doctor first.
- "British Journal of Nutrition;" High alpha-linolenic acid flaxseed (Linum usitatissimum): some nutritional properties in Humans; S. Cunnane, et al.; March 1993
- MayoClinic.com; Flaxseed and Flaxseed Oil; April 2011
- "PLoS One;" Effects of a Flaxseed-Derived Lignan Supplement in Type 2 Diabetic Patients: A Randomized, Double-Blind, Cross-Over Trial; A Pan et al.; November 2007
- "Journal of Oleo Science;" High Dose Flaxseed Oil Supplementation May Affect Fasting Blood Serum Glucose Management in Human Type 2 Diabetics; D. Barre, et al.; 2008 cs;
- University of Maryland Medical Center; Flaxseed Oil; May 2010
- Dietaryfiberfood.com: Total Dietary, Soluble and Insoluble Fiber Content of Foods: Vegetables, Fruits and Legumes