Flaxseed Fiber [Discontinued] by Moss Nutrition

POSSIBLY EFFECTIVE

• Constipation. Oral flaxseed is a bulk forming laxative that helps to relieve constipation. Details: Flaxseed is a source of dietary fiber and has a bulk forming laxative effect (6803,12910). One clinical study in healthy young adults shows that consuming muffins containing 25 grams of milled flaxseed twice daily for 4 weeks increases weekly bowel movements by 30% when compared to a control group (6803). Other clinical research in diabetic patients with constipation shows that taking flaxseed 10 grams twice daily for 12 weeks improves stool form and reduces constipation by a moderate amount when compared with placebo (101950). Furthermore, a small clinical study in patients in China with functional constipation shows that consuming brown flaxseed flour 50 grams in divided doses with meals daily for 4 weeks seems to modestly improve frequency of bowel movements and pain and reduce failure to evacuate when compared with taking lactulose 15 mL every morning (105474). Flaxseed has also been evaluated in combination with other natural ingredients. A preliminary clinical trial in elderly patients with mild constipation shows that eating yogurt containing galacto-oligosaccharide syrup (Elixor, Borculo Whey Products) 6 grams, prunes 6 grams, and flaxseed 3 grams twice daily for 3 weeks increases stool frequency when compared with a control yogurt (21191). It is unclear if the effects were due to flaxseed, other constituents, or the combination.
• Diabetes. Oral ground flaxseed modestly reduces blood glucose in patients with diabetes and pre-diabetes. It is unclear if oral whole flaxseed reduces blood glucose. Details: Most evidence from meta-analyses and clinical research in adults with prediabetes and diabetes shows that taking ground flaxseed reduces fasting blood glucose and insulin levels (21194,21196,26479,101950,111061). A meta-analysis of 7 small to moderate clinical trials shows that taking flaxseed, usually ground, 13 to 40 grams daily for 8-12 weeks has a small beneficial effect on fasting blood glucose, insulin, insulin resistance, and glycated hemoglobin (HbA1c), compared with no intervention or another fiber source. A sub-analysis shows that the benefit of flaxseed on fasting glucose levels remains in patients with type 2 diabetes (111061). Other research disagrees. A meta-analysis of three small clinical trials in patients with type 2 diabetes shows that taking flaxseed does not improve fasting blood glucose, insulin resistance, or HbA1c (111062). Another meta-analysis of 24 clinical studies involving 1,879 patients with and without diabetes shows that whole and ground flaxseed seem to reduce blood glucose levels by an average of 6 mg/dL and insulin levels by an average of 1 mIU/mL and modestly reduce insulin resistance when compared with control treatments such as wheat germ or raw rice. Whole and ground flaxseed were not shown to significantly reduce HbA1c when compared with control, although there was a non-significant trend towards a reduction (96428). Significant heterogeneity in study size and study population limit the validity of these findings. The effects of flaxseed lignan extract in patients with type 2 diabetes is unclear. A small clinical study in Chinese adults with type 2 diabetes show that using a specific standardized flaxseed lignan extract (Flax Essence, Jarrow Formulas) 600 mg three times daily, providing 360 mg secoisolariciresinol diglucoside, slightly reduces HbA1c when compared with placebo (16768). However, a small meta-analysis including this study shows that taking flaxseed lignans does not reduce fasting blood glucose or HbA1c (111062).
• Hypercholesterolemia. Oral whole and ground flaxseed modestly reduce lipid levels. Details: Most research shows that taking various flaxseed preparations 30-50 grams daily reduces total cholesterol by 5% to 15% and low-density lipoprotein (LDL) cholesterol by 8% to 18%, but does not seem to affect high-density lipoprotein (HDL) cholesterol, when compared with control (6808,10952,22179,26478,65866,101944,101947,101949,108044,108046)(111064). Apolipoprotein A-1 and apolipoprotein B may be reduced by 6% and 7.5%, respectively (10952). A meta-analysis of clinical studies shows reductions in apolipoprotein A and apolipoprotein B following whole flaxseed supplementation (108046). The cholesterol-lowering effect of flaxseed has been shown in various populations, including those with hypercholesterolemia with/or without diabetes, postmenopausal patients, and patients with chronic kidney disease or cardiovascular risk factors (6808,10952,10978,12910,22180,22181,26478,26480,26488,101944)(101949,101950,111064). One large meta-analysis suggests that the most consistent effect occurs in patients with hypercholesterolemia (101947). Another large meta-analysis suggests that patients with hypercholesterolemia and healthy patients with a body mass index greater than 25 kg/m2 may benefit the most from treatment (108044). Most research shows that flaxseed reduces triglyceride levels (101947,108046,111064). However, there are certain preparations, such as partially defatted flaxseed (which lacks alpha-linolenic acid content) or flaxseed incorporated into bread products, which might increase triglyceride levels by up to 26% (6808,26488).
• Hypertension. Daily oral flaxseed consumption, especially for longer than 12 weeks, seems to modestly reduce blood pressure. Details: Meta-analyses of mainly small clinical studies in patients with and without hypertension show that taking flaxseed reduces systolic and diastolic blood pressure by an average of 1.1 to 1.8 and 1.0 to 1.3 mmHg, respectively, when compared with control (96426,111063). The effect of flaxseed lignan is unclear. One meta-analysis shows that flaxseed lignan does not seem to reduce blood pressure when compared with control (96426). However, a more recent meta-analysis shows that taking flaxseed lignan has a small effect on systolic, but not diastolic, blood pressure (111063). The length of supplementation may play a role as studies lasting longer than 12 weeks seemed to lower blood pressure to a slightly greater degree than studies lasting less than 12 weeks (96426). The validity of these findings is limited due to the short duration of treatment, the variation in study size, the inclusion of patients with and without hypertension, and the range of doses used. Some clinical research also shows that taking flaxseed may be beneficial for blood pressure reduction in patients with hypertension (111063). One individual clinical study in adults with hypertension shows that taking flaxseed 10 grams or 30 grams daily affects blood pressure in a dose-dependent manner when compared with placebo. After 12 weeks of treatment, systolic and diastolic blood pressure decreased by 12 mmHg and 6 mmHg, respectively, in the high-dose group, compared with 10 mmHg and 7 mmHg, respectively, in the low-dose group (108043).
• Mastalgia. Oral flaxseed seems to reduce symptoms of cyclic mastalgia. Details: Clinical research in healthy Iranian women with cyclic mastalgia shows that taking flaxseed powder 25 grams daily for 2 months reduces breast pain intensity from moderate to mild and also reduces duration of pain when compared with placebo (96250). Other preliminary clinical research shows that eating a muffin containing ground flaxseed 25 grams daily for 3 months reduces symptoms of severe cyclic mastalgia (16766).
• Obesity. Oral flaxseed and flaxseed mucilage seem to modestly improve weight loss in patients who are obese or overweight. However, flaxseed lignan extract does not seem to be beneficial. Details: A meta-analysis of 45 clinical studies including 2,561 overweight or obese adults shows that flaxseed consumption reduces body weight by 1.8 kg, body mass index (BMI) by 0.6 kg/m2, and waist circumference by 1.2 cm when compared with control in adults. The most benefit is seen in adults with a baseline BMI greater than or equal to 27 (96427). Flaxseed consumption of at least 30 grams daily for durations of at least 12 weeks demonstrated the greatest efficacy (96427,101949). The soluble fiber, flaxseed mucilage, has also been studied. A clinical trial in overweight or obese adults shows that taking oral flaxseed mucilage 1280 or 2560 mg mixed in water twice daily with meals for 12 weeks decreases body weight, waist circumference, and BMI in a dose-dependent manner when compared with placebo. After 12 weeks, a 5 kg and 4 kg weight reduction was observed in the high- and low-dose groups, respectively, compared to a 1 kg reduction in the placebo group (108047). The validity of this finding is limited due to short duration of treatment and lack of follow-up. Conversely, flaxseed lignan extract does not appear to be effective in reducing weight, BMI, or waist circumference (96427). Some research has investigated whether variants in genes related to satiety and appetite play a role in any effect of flaxseed on weight loss and appetite. A small clinical trial in adults with overweight or obesity shows that taking defatted flaxseed flour in biscuits daily for 8 weeks modestly reduces body weight, BMI, triglycerides, or blood glucose only in those with specific gene variants when compared with control biscuits (111066). More information is needed to determine how these gene variants play a role in the connection between nutrition and obesity.
• Systemic lupus erythematosus (SLE) nephritis. Oral flaxseed might be beneficial for improving kidney function in SLE. Details: Some small clinical studies suggest that taking whole or ground flaxseed orally might improve serum creatinine levels in people with SLE nephritis (6802,8021).

POSSIBLY INEFFECTIVE

• Osteoporosis. Oral flaxseed does not seem to be beneficial in osteoporosis. Details: Clinical research shows that consuming ground flaxseed 40 grams daily for up to one year does not affect markers of bone metabolism or improve bone mineral density in healthy, postmenopausal adults (10952,12910). Similarly, taking flaxseed extract 550 mg three times daily for 6 months does not appear to improve bone mineral density when compared with placebo in older adults (21197).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Acne. Although there is interest in using oral flaxseed for acne, there is insufficient reliable information about the clinical effects of flaxseed for this purpose.
• Benign prostatic hyperplasia (BPH). It is unclear if oral flaxseed lignan improves symptoms of BPH. Details: A small clinical study in patients with BPH shows that taking a specific flaxseed lignan extract (BeneFlax, Archer Daniels Midland Co.) 300 mg or 600 mg daily for 4 months improves lower urinary tract symptom scores when compared with placebo. Additionally, the 600 mg dose was associated with improved quality of life when compared with placebo (21193).
• Breast cancer. It is unclear if oral flaxseed reduces the risk for breast cancer or the progression of breast cancer. Details: A small clinical study in females newly diagnosed with breast cancer shows that consuming a muffin containing ground flaxseed 25 grams daily for about 40 days reduces markers of tumor cell proliferation when compared with baseline, but not when compared with placebo (16765). The effect of flaxseed intake on breast cancer outcomes was not assessed. Dietary lignans, which occur in flaxseed, have been linked with a lower risk of developing breast cancer. Most large-scale population studies have found that high intake of dietary lignans and serum levels of the lignan enterolactone are associated with a reduced risk of developing breast cancer (16775,16776,16777,16779,16781,16782,16783,16785). It is unclear if flaxseed lignan, specifically, is beneficial for reducing the risk of breast cancer.
• Burning mouth syndrome. Flaxseed has only been evaluated in a mouthwash in combination with German chamomile; its effect when used alone is unclear. Details: A small clinical study in female patients with burning mouth syndrome shows that using a homemade mouthwash containing boiled whole flaxseed 10 grams and German chamomile 1 gram in 200 mL of water 3-4 times daily for 3 months decreases subjective burning and dry mouth symptoms, increases salivary flow rate, and decreases saliva viscosity when compared with baseline (104807). However, the validity of these results is limited by the lack of a control group and product standardization, as the mouthwash was prepared by each patient from ingredients they purchased.
• Cardiovascular disease (CVD). It is unclear if oral flaxseed or flaxseed lignans reduce the development or progression of CVD. Details: A small clinical study in older adults that were also given dietary advice shows that taking flaxseed 30 grams daily for 12 weeks, starting 4 weeks after percutaneous coronary intervention (PCI), more than doubles flow mediated dilation when compared with a group not taking flaxseed (101945). However, population research has found that total dietary intake of lignans, including flaxseed lignans, is not associated with a reduced risk of coronary heart disease or all-cause mortality (16787). This research did not specifically assess the effect of flaxseed intake on CVD.
• Chronic kidney disease (CKD). Although there is interest in using oral flaxseed for CKD, there is insufficient reliable information about the clinical effects of flaxseed for this condition.
• Colorectal cancer. It is unclear if oral flaxseed reduces the risk of colorectal cancer. Details: Flaxseed is one source of dietary lignans. Population research has found that serum levels of lignans are not associated with risk of developing colorectal cancer (16778). However, other population research has found that high dietary intake of lignans is associated with a reduced risk of colorectal cancer (16784), and that higher serum levels of dietary lignans are associated with a reduced risk of colorectal adenomas (16788). It is unclear if flaxseed lignan, specifically, is beneficial for reducing the risk of colorectal cancer.
• Endometrial cancer. It is unclear if oral flaxseed reduces the risk of endometrial cancer. Details: Flaxseed is one source of dietary lignans. A large-scale population study has found that serum levels of lignans are not associated with risk of developing endometrial cancer (16786).This research did not specifically assess the effect of flaxseed intake on endometrial cancer risk.
• Fatigue. It is unclear if oral ground flaxseed reduces fatigue in overweight children. Details: A small non-blinded clinical study in overweight healthy children ages 7-18 shows that consuming ground flaxseed 20 grams in divided doses with food daily for 4 weeks seems to modestly reduce mental fatigue but not physical fatigue when compared with puffed wheat 25 grams daily (105473).
• Impaired glucose tolerance (prediabetes). It is unclear if oral flaxseed is beneficial in prediabetes. Details: A small clinical study in adults with prediabetes shows that consuming milled flaxseed 20 grams or 40 grams daily for 12 weeks does not improve glycemic control, but modestly reduces systolic blood pressure, when compared with no intervention (96434).
• Irritable bowel syndrome (IBS). It is unclear if oral flaxseed improves IBS symptoms. Details: A small open-label clinical study in patients with IBS suggests that consuming whole or ground flaxseed 24 grams daily for 4 weeks does not improve quality of life, severity of IBS symptoms, or number of bowel movements when compared with no intervention (21198).
• Lung cancer. It is unclear if oral flaxseed reduces the risk of lung cancer. Details: Observational research has found that consuming a higher amount of dietary phytoestrogens, such as the lignan metabolites and precursors found in flaxseed, is associated with a lower risk of developing lung cancer when compared to those who consume smaller amounts (13190). It is unclear if flaxseed, specifically, is beneficial for reducing the risk of lung cancer.
• Menopausal symptoms. There is contradictory evidence about the effects of flaxseed for reducing menopausal symptoms. Details: Some preliminary clinical research in postmenopausal adults shows that taking either flaxseed meal 90 grams daily or a specific flaxseed extract (Biogalenica, Medicinal Compounding Pharmacy) 1000 mg daily for 6 months reduces menopausal symptoms and the frequency of hot flashes when compared to baseline (21200). Other small clinical studies in postmenopausal adults show that consuming ground flaxseed orally 40 grams daily reduces symptoms of hot flashes by about 35% and night sweats by about 44% when compared to baseline (10978,12910). However, similar reductions have been observed with placebos, such as wheat germ (12910,18224). Higher quality studies of flaxseed used in food products have yielded negative results. One clinical trial in postmenopausal adults shows that taking a specific flaxseed-containing bar (Glambia Nutritionals) providing 7 grams of flaxseed and 410 mg of lignans reduces hot flash frequency by 28% and hot flash scores by 50% when compared to baseline, but not when compared with placebo (18224). In another small clinical study, consuming muffins containing flaxseed 25 grams daily providing 50 mg lignans did not improve hot flashes or measures of quality of life when compared with placebo in a similar patient population (16762). Eating flaxseed-enriched bread providing 25 grams of flaxseed daily for 12 weeks also did not improve menopausal symptoms or reduce the frequency of hot flashes when compared to control (22176).
• Metabolic syndrome. Small studies suggest that oral flaxseed is beneficial for metabolic syndrome. Details: One small clinical study in older adults shows that taking a specific flaxseed lignan extract (BeneFlax, Archer Daniels Midland Co.) 550 mg three times daily for 6 months reduces metabolic syndrome risk scores when compared with placebo in males, but not females (21197). Another small open-label clinical trial in patients with metabolic syndrome suggests that taking flaxseed powder 30 grams daily for 12 weeks modestly reduces the number of people meeting the criteria for metabolic syndrome when compared with no supplementation (105276). However, food containing flaxseed does not seem to be as beneficial. Some clinical research in Asian Americans with metabolic syndrome shows that eating bread containing flaxseed 30 grams daily plus lifestyle counseling for 12 weeks does not improve markers of metabolic syndrome when compared with lifestyle counseling alone (21199).
• Nonalcoholic fatty liver disease (NAFLD). Small clinical studies suggest that oral flaxseed may modestly reduce markers of liver disease progression in patients with NAFLD. Details: A small clinical pilot study in adults with NAFLD shows that taking brown milled flaxseed 30 grams daily for 12 weeks along with lifestyle modification reduces fibrosis by 21% and steatosis by about 15.3%, compared with reductions of 9.7% and 5.5%, respectively, in those following lifestyle modifications alone (96249). A larger follow-up clinical study in patients with NAFLD shows that taking brown milled flaxseed 30 grams daily for 12 weeks in addition to lifestyle modification reduces steatosis by about 28%, compared with a 16% reduction in the lifestyle modification group (105275).
• Osteoarthritis. It is unclear if topical flaxseed is beneficial in patients with osteoarthritis. Details: A small clinical study in patients with hand osteoarthritis who are using routine treatments shows that using a flaxseed poultice compress once daily for 7 days improves pain by 63% and hand function by 66% when compared with a hot compress or no compress in combination with routine treatments. Some of the benefit was maintained for at least a week following treatment (101946).
• Peripheral arterial disease (PAD). It is unclear if oral flaxseed is beneficial in patients with PAD. Details: Clinical research in patients with PAD shows that taking milled flaxseed 30 grams daily mixed with a variety of foods for one year does not reduce the incidence of cardiac arrhythmias or improve the distance walked until claudication when compared with placebo (101942). This study may have been inadequately powered to detect differences between groups.
• Pharyngitis. Although there is interest in using oral flaxseed for pharyngitis, there is insufficient reliable information about the clinical effects of flaxseed for this purpose.
• Polycystic ovary syndrome (PCOS). It is unclear if oral flaxseed is beneficial in patients with PCOS. Details: A small open-label clinical study in patients with PCOS shows that taking flaxseed 30 grams daily for 12 weeks in conjunction with receiving lifestyle modification advice reduces triglyceride and insulin levels and improves insulin resistance when compared with lifestyle modification advice alone. About 69% of those in the treatment group who had irregular menstrual cycles at baseline had a regular cycle at the end of treatment, compared with no significant improvement in the control group. Flaxseed did not affect body weight, low-density lipoprotein (LDL) cholesterol, or blood glucose when compared with control (101943).
• Prostate cancer. Small clinical studies suggest that oral flaxseed may modestly improve biomarkers of prostate cancer. Details: A very small clinical trial in patients with prostatic intraepithelial neoplasia (PIN), a precancerous proliferation of prostatic epithelial cells, shows that adding ground flaxseed (Alena, Enreco) 30 grams daily to a fat-restricted diet for 6 months lowers prostate specific antigen (PSA) levels and slows prostate epithelium proliferation when compared with baseline (12908). This finding is limited by the lack of a placebo group. A clinical study in patients with prostate cancer awaiting prostatectomy shows that taking ground flaxseed (Alena, Enreco) 30 grams daily with or without a fat-restricted diet for about 30 days reduces tissue proliferation rate, but does not reduce PSA, when compared with control (16761).
• Radiation-induced pneumonitis. It is unclear if oral flaxseed is beneficial for preventing radiation-induced pneumonitis in patients with non-small cell lung cancer (NSCLC). Details: A very small, clinical trial in adults with locally advanced or metastatic NSCLC currently undergoing chemoradiation therapy shows that taking ground flaxseed (Golden Valley Flax; Hylden Farms) 40 grams daily, starting one week prior to radiotherapy and continuing until completion of treatment, may reduce the risk of radiation-induced pneumonitis when compared with baseline, with only 1 patient (5%) developing a grade ≥3 event and no cases of grade 2 events (108042). The validity of these findings is limited by the lack of a comparator group and a low adherence rate due to tolerability issues.
• Rheumatoid arthritis (RA). It is unclear if oral flaxseed is beneficial in patents with RA. Details: A clinical study in adults with RA shows that following either a regular or anti-inflammatory diet supplemented with oral flaxseed 30 grams daily for 12 weeks improves disease activity score 28-joint (DAS28-ESR), as well as pain and quality of life outcomes, such as emotional well-being and vitality, when compared with baseline (108048). The validity of these findings is limited by the lack of a comparator group.
• Ulcerative colitis. It is unclear if oral flaxseed is beneficial in patients with ulcerative colitis. Details: A small open-label clinical study in patients with ulcerative colitis shows that taking ground flaxseed 30 grams daily for 12 weeks seems to modestly reduce inflammatory markers and disease severity and improve quality of life when compared with control (101941). A nonblinded, clinical study in adults with mild to moderate ulcerative colitis shows that taking brown milled flaxseed 15 grams twice daily for 12 weeks improves disease severity scores when compared with placebo (108045). The validity of these findings is limited by the lack of blinding and short duration of treatment. More evidence is needed to rate flaxseed for these uses.

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LIKELY SAFE ...when ground flaxseed is used orally and appropriately. Ground flaxseed has been safely used in numerous clinical trials in doses up to 30-60 grams daily for up to 1 year (6803,6808,8020,10952,10978,12908,12910) (16760,16761,16762,16765,16766,18224,21191,21194,21196,21198) (21199,21200,22176,22179,22180,22181,65866,66065) (101943,101949,101950).

POSSIBLY SAFE ...when flaxseed lignan extract or mucilage is used orally and appropriately. Some clinical research shows that a specific flaxseed lignan extract (Flax Essence, Jarrow Formulas) 600 mg daily can be used with apparent safety for up to 12 weeks (16768). Additional clinical research shows that other flaxseed lignin extracts can be used with apparent safety for up to 6 months (21193,21197,21200). In one clinical trial, flaxseed mucilage was used with apparent safety at a dose of up to 5120 mg daily for up to 12 weeks (108047)....when flaxseed is used topically in a warm poultice (101946).

POSSIBLY UNSAFE ...when raw or unripe flaxseed is used orally. Raw flaxseed contains potentially toxic cyanogenic glycosides (linustatin, neolinustatin, and linamarin); however, these glycosides have not been detected after flaxseed is baked (5899). Unripe flaxseeds are also thought to be poisonous when consumed due to cyanide content.

PREGNANCY: POSSIBLY UNSAFE
when used orally. Flaxseed can have mild estrogenic effects. Theoretically, this might adversely affect pregnancy (9592,12907); however, there is no reliable clinical evidence about the effects of flaxseed on pregnancy outcomes.

LACTATION:
Insufficient reliable information available; avoid using.

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ANTIBIOTIC DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, antibiotics might interfere with the metabolism of flaxseed constituents, which could potentially alter the effects of flaxseed.  Details Some potential benefits of flaxseed are thought to be due to its lignan content. Secoisolariciresinol diglucoside (SDG), a major lignan precursor, is found in high concentrations in flaxseed. SDG is converted by bacteria in the colon to the lignans enterolactone and enterodiol (5897,8022,8023,9592). Antibiotics alter the flora of the colon, which could theoretically alter the metabolism of flaxseed.

ANTICOAGULANT/ANTIPLATELET DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = High •  Occurrence = Possible •  Level of Evidence = B Theoretically, using flaxseed in combination with anticoagulant or antiplatelet drugs might have additive effects and increase the risk of bleeding.  Details Some clinical evidence suggests that the oil contained in flaxseed can decrease platelet aggregation (5898,21912).

ANTIDIABETES DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Probable •  Level of Evidence = B Theoretically, flaxseed might have additive effects when used with antidiabetes drugs and increase the risk for hypoglycemia.  Details Some clinical research suggests that flaxseed can lower blood glucose levels (5899,10978,21194,21196,111061).

ANTIHYPERTENSIVE DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, flaxseed might have additive effects when used with antihypertensive drugs and increase the risk of hypotension.  Details Clinical research shows that daily flaxseed consumption, especially for longer than 12 weeks, modestly reduces blood pressure (21197,26487,96426,96428,111063).

ESTROGENS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, taking flaxseed might decrease the effects of estrogens.  Details Flaxseed contains lignans with mild estrogenic and possible antiestrogenic effects. The lignans seem to compete with circulating endogenous estrogen and might reduce estrogen binding to estrogen receptors, resulting in an anti-estrogen effect (8868,9593). It is unclear if this effect transfers to exogenously administered estrogens.

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General ...Orally, flaxseed is usually well-tolerated.
Most Common Adverse Effects:
Orally: Bloating, diarrhea, gastrointestinal complaints.
Serious Adverse Effects (Rare):
Orally: Severe allergic reactions such as and anaphylaxis.

Gastrointestinal ...Integrating flaxseed in the diet can cause digestive symptoms similar to other sources of dietary fiber including bloating, fullness, flatulence, abdominal pain, diarrhea, constipation, dyspepsia, and nausea (12910,16761,16765,21198,21200,22176,22179,65866,101943). Higher doses are likely to cause more gastrointestinal side effects. Flaxseed can significantly increase the number of bowel movements and the risk for diarrhea (6803,8021,16765). Doses greater than 45 grams per day may not be tolerated for this reason (6802). Metallic aftertaste and bowel habit deterioration have also been reported in a clinical trial (21198).
There is some concern that taking large amounts of flaxseed could result in bowel obstruction due to the bulk forming laxative effects of flaxseed. Bowel obstruction occurred in one patient in a clinical trial (65866). However, this is not likely to occur if flaxseed is consumed with an adequate amount of fluids.

Immunologic ...Occasionally, allergic and anaphylactic reactions have been reported after ingestion of flaxseed (16761). Handling and processing flaxseed products might increase the risk of developing a positive antigen test to flaxseed and hypersensitivity (6809,12911,26471,26482).

Oncologic ...Flaxseed contains alpha-linolenic acid (ALA). High dietary intake of ALA has been associated with increased risk for prostate cancer (1337,2558,7823,7147,12978). However, ALA from plant sources, such as flaxseed, does not seem to increase this risk (12909).

Other ...Orally, partially defatted flaxseed, which is flaxseed with less alpha-linolenic acid, might increase triglyceride levels (6808). Raw or unripe flaxseed contains potentially toxic cyanogenic glycosides (linustatin, neolinustatin, and linamarin). These chemicals can increase blood levels and urinary excretion of thiocyanate in humans. However, these glycosides have not been detected after flaxseed is baked (5899).

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