Flaxseed

Dietary flaxseed: preliminary evidence of anticancer action among people with breast cancer eating flaxseed

• Less tumor cell proliferation, lower markers of cell growth, and higher cell death (apoptosis), among postmenopausal women with newly diagnosed breast cancer eating flaxseed compared to placebo in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹Thompson LU, Chen JM, Li T, Strasser-Weippl K, Goss PE. Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clinical Cancer Research. 2005 May 15;11(10):3828-35.

Flaxseed supplements: weak evidence of anticancer action among women at risk for breast cancer after supplementation with a lignan found in flax

• Lower levels of a biomarker for tumor cell proliferation in benign breast tissue of premenopausal women at risk for breast cancer after supplementation with a lignan found in flax compared to baseline in a small uncontrolled triala study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design²Fabian CJ, Kimler BF, et al. Reduction in Ki-67 in benign breast tissue of high-risk women with the lignan secoisolariciresinol diglycoside. Cancer Prevention Research. 2010 Oct;3(10):1342-50.

• Lower proliferation rates but no change in cell death (apoptosis) or cancer biomarkers before surgery among men with prostate cancer adding flaxseed to their diets compared to controls in a mid-size RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects of moderate quality³Demark-Wahnefried W, Polascik TJ et al. Flaxseed supplementation (not dietary fat restriction) reduces prostate cancer proliferation rates in men presurgery. Cancer Epidemiology, Biomarkers & Prevention. 2008 Dec;17(12):3577-87; Hackshaw-McGeagh LE, Perry RE et al. A systematic review of dietary, nutritional, and physical activity interventions for the prevention of prostate cancer progression and mortality. Cancer Causes and Control. 2015 Nov;26(11):1521-50.
• 23% lower levels of a tumor biomarker among men with localized prostate cancer adding ground flaxseed to their diets for 30 days compared to controls in a mid-sized RCT⁴Azrad M, Vollmer RT et al. Flaxseed-derived enterolactone is inversely associated with tumor cell proliferation in men with localized prostate cancer. Journal of Medicinal Food. 2013 Apr;16(4):357-60.

Dietary flaxseed: modest evidence of better markers of blood sugar and insulin sensitivity among people adding flaxseed to their diets

• Better blood sugar control and insulin levels and sensitivity among people eating whole flaxseed for 12 weeks or more in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 12 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁵Mohammadi-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. Nutrition Reviews. 2018 Feb 1;76(2):125-13.
• Lower fasting plasma glucose, but no change in plasma insulin, among glucose-intolerant people with obesity adding ground flaxseed to their diets for 12 weeks compared to controls adding wheat bran in a small RCT⁶Rhee Y, Brunt A. Flaxseed supplementation improved insulin resistance in obese glucose intolerant people: a randomized crossover design. Nutrition Journal. 2011 May 9;10:44.
• Better peak blood glucose levels among healthy people after eating flax bread compared to white bread in a small RCT⁷Dahl WJ, Lockert EA, Cammer AL, Whiting SJ. Effects of flax fiber on laxation and glycemic response in healthy volunteers. Journal of Medicinal Food. Winter 2005;8(4):508-11.

Flaxseed supplements: no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on blood sugar or insulin sensitivity among people using flaxseed oil and lignan extract in a combined analysis of studies

• No change in blood sugar control, insulin levels and sensitivity among people using flaxseed oil and lignan extract compared to controls in a meta-analysis of 12 RCTs⁸Mohammadi-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. Nutrition Reviews. 2018 Feb 1;76(2):125-13.

• Lower testosterone and estrone among postmenopausal women without cancer who are obese after eating ground flaxseeds compared to baseline in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study, and a weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently) toward lower levels of estradiol, estrone, and testosterone among postmenopasual women without cancer who are not obese⁹Sturgeon SR, Heersink JL et al. Effect of dietary flaxseed on serum levels of estrogens and androgens in postmenopausal women. Nutrition and Cancer. 2008;60(5):612-8.