Do flax seeds help with weight loss?

Slightly. A 2024 meta-analysis of 64 trials found flaxseed products lowered body weight by 1.4 lb (0.63 kg) on average (95% CI 0.6 to 2.2 lb (0.27 to 1.00 kg)) and waist size by 0.56 in (1.43 cm), against control. The authors graded that evidence moderate. The trials disagreed with each other a lot, and most were not blinded. The effect was larger in people with a BMI above 30. In people with coronary artery disease, five trials found no change in weight or BMI.

Established. On average, flaxseed lowers weight by under a kilogram. A 2024 meta-analysis of 64 trials put it at 1.4 lb (0.63 kg), and an older one of 45 randomized trials put it at 2.2 lb (95% CI 0.68 to 3.7; metric: 0.99 kg, 0.31 to 1.67). The two reviews draw on many of the same trials.

What the trials found

The pooled reviews

Besides weight, the 2024 review found BMI 0.24 lower and waist 0.56 in (1.43 cm) smaller (95% CI 0.31 to 0.81 in (0.80 to 2.06 cm)). In its subgroups the effect was larger in trials that lasted 10 to 20 weeks and in people whose BMI was above 30. Those subgroup gaps come from comparing different trials with each other, which is weaker than testing the question directly. The 2017 review of 45 randomized trials pointed the same way. In its subgroups the benefit appeared with whole flaxseed at 30 g a day or more, taken for 12 weeks or longer, in people with a BMI of 27 or more.

In type 2 diabetes, a 2025 meta-analysis of 16 trials in 1136 people found flaxseed reduced weight and waist size, and the change in BMI did not reach significance. It reported only standardized differences, with very high disagreement between trials, so the size in kilograms is unknown. In coronary artery disease, a 2024 meta-analysis of 5 trials found a weight difference of 0.11 lb (0.05 kg) (95% CI 0.62 lb (0.28 kg) gained to 0.86 lb (0.39 kg) lost) and no change in BMI. Weight was not the main aim of those trials.

The trials with big numbers

Myth. Flaxseed does not take off nine kilos. That number comes from one 12-week trial in 50 overweight and obese adults, where 30 g a day of milled flaxseed plus lifestyle advice gave 21 lb (9.36 kg) of weight loss against 6.8 lb (3.09 kg) with advice alone. The trial was small and unblinded, it had no placebo, and its 13 lb (6 kg) gap is far above the pooled average of under 2.2 lb (1 kg).

A second trial with a large gap tested a different product. In 108 overweight adults on a calorie-reduced diet, a fiber extract made from flaxseed mucilage gave 11 lb (4.96 kg) of weight loss at the high dose and 8.2 lb (3.70 kg) at the low dose, against 2.9 lb (1.33 kg) on placebo, over 12 weeks. It is a single trial of a proprietary extract, and its result does not carry over to the seed you buy in a shop.

Two trials of 30 g a day of the seed itself, in people who were not recruited for their weight, came out small or null. In 70 people with ulcerative colitis, 12 weeks of ground flaxseed did not change weight, BMI or waist against control. In 112 people with high blood pressure, 12 weeks lowered BMI by 0.86 units against 0.06 on placebo.

Who should be careful

Of the 64 trials in the 2024 review, only 3 tested their flaxseed product for purity, and none mentioned the risk of heavy metal contamination. That is a gap in reporting, and it is not evidence of contamination. In a separate 4-week crossover trial in 80 volunteers eating flaxseed foods, blood cadmium and serum thiocyanate stayed within reference values. In the mucilage extract trial, adverse events were mainly respiratory infections and gut symptoms, and none were judged related to the extract. In 34 healthy adults, 40 g a day of milled flaxseed in a muffin for 30 days caused no adverse events, with 8 to 9 people in each dose group.

Not for everyone. Raw ground flaxseed releases cyanide compounds. In healthy women eating 1.8 oz (50 g) of raw ground flaxseed a day for 4 weeks, urinary thiocyanate, a marker of cyanide exposure, rose 2.2-fold. That was a 1993 study with no control group, and in muffins baked with flaxseed the cyanogenic glycosides could not be detected. EU law sets maximum levels of hydrocyanic acid in linseed because, in the regulator's words, raw ground linseed exposes a person to more cyanide than whole or heat-treated seed. Those findings favor baked or cooked flaxseed over raw ground seed.

Not for everyone. If you take regular medicines, check with your pharmacist before taking flaxseed as a supplement. In a review of 1,491 documented supplement and drug interaction pairs, flaxseed was one of the three supplements with the most documented contraindications. That review counts documentation, not harm to patients, and its abstract does not say which conditions or drugs are involved.

We did not find evidence on flaxseed for weight loss in pregnancy or in children, so this page cannot say anything about them either way.

What expert bodies say

We found no agency position on flaxseed for weight. The US Office of Dietary Supplements has no flaxseed fact sheet, and neither the EU nor the US has an authorized weight claim for flaxseed or linseed. On safety, the EU regulates linseed through the hydrocyanic acid limits described above.

How we searched

What would change this answer

• A placebo-controlled trial of whole milled flaxseed lasting 6 months or more, with weight as its main outcome. The local copy of ClinicalTrials.gov lists no such trial that is active.
• A blinded repeat of the 50-person lifestyle trial. Its 13 lb (6 kg) gap is the largest weight result on this page, and nobody has repeated it.
• Trials that test their flaxseed for purity and heavy metals and report it.

Flaxseed's fiber, omega-3 fat and the trials on blood pressure and cholesterol are on the flaxseed page.

Sources

1. ev-flxw-01 · Meta-analysis or systematic review · systematic review and random-effects meta-analysis of clinical trials, GRADE assessment · n = 64 trials, 72 treatment arms
   Our meta-analysis revealed significant reductions in body weight (WMD = -0.63 kg; 95 % CI: -1.00, -0.27, P < 0.001; I2 = 76.7 %, P < 0.001), body mass index (BMI) (WMD: -0.24 kg/m2, 95 % CI: -0.36, -0.11, P < 0.001; I2 = 78.5 %, P < 0.001) and waist circumference (WC) (WMD: -1.43 cm, 95 % CI: -2.06, -0.80, P < 0.001; I2 = 81.1 %, P < 0.001) following flaxseed supplementation.
   
   Who: adults in clinical trials of lignans, whole flaxseed or flaxseed oil
   Effect: weight WMD -1.4 lb (95% CI -2.2 to -0.6; metric: -0.63 kg, -1.00 to -0.27), I2 76.7%; BMI WMD -0.24 kg/m2 (95% CI -0.36 to -0.11); waist WMD -0.56 in (95% CI -0.81 to -0.31; metric: -1.43 cm, -2.06 to -0.80)
   Certainty: GRADE moderate per the authors, but heterogeneity is high and most trials were not blinded; the average loss is under 2.2 lb (1 kg).
   Complement Ther Med, 2024 · checked 2026-10-07 · we read the abstract
2. ev-flxw-02 · Meta-analysis or systematic review · systematic review and meta-analysis, subgroup analysis and GRADE · n = 64 trials
   Subgroup analyses indicated that interventions lasting 10-20 weeks, and studies involving subjects with higher BMI (>30 kg/m2) showed more significant anti-obesity effects. Based on the GRADE evaluation, body weight, BMI, and WC results were considered as moderate-certainty evidence.
   
   Who: adults in clinical trials of flaxseed products
   Effect: larger effect with 10-20 week interventions and baseline BMI > 30 kg/m2; GRADE moderate for weight, BMI and waist
   Certainty: Subgroup differences are observational comparisons across trials.
   Complement Ther Med, 2024 · checked 2026-10-07 · we read the abstract
3. ev-flxw-03 · Meta-analysis or systematic review · systematic review and meta-analysis of clinical trials · n = 64 trials
   However, three studies did testing for purity, and 40 studies reported potency. Also, the risk of contamination with heavy metals was not mentioned in studies. Another limitation was the lack of blind evaluation in the studies.
   
   Who: clinical trials of flaxseed products
   Effect: purity tested in 3 trials; potency reported in 40; heavy metal contamination not mentioned in any
   Certainty: A gap in reporting, not evidence of contamination; flaxseed cadmium and cyanogenic glycosides are carded in cards_daily_flaxseed.py.
   Complement Ther Med, 2024 · checked 2026-10-07 · we read the abstract
4. ev-flxw-04 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 45 RCTs
   Meta-analyses suggested a significant reduction in body weight (WMD: -0.99 kg, 95% CI: -1.67, -0.31, p = 0.004), BMI (WMD: -0.30 kg m-2 , 95% CI: -0.53, -0.08, p = 0.008) and waist circumference (WMD: -0.80 cm, 95% CI: -1.40, -0.20, p = 0.008) following flaxseed supplementation. Subgroup analyses showed that using whole flaxseed in doses ≥30 g d-1 , longer-term interventions (≥12 weeks) and studies including participants with higher BMI (≥ 27 kg m-2 ) had positive effects on body composition.
   
   Who: participants in RCTs of flaxseed supplementation up to November 2016
   Effect: weight WMD -2.2 lb (95% CI -3.7 to -0.68; metric: -0.99 kg, -1.67 to -0.31); BMI WMD -0.30 kg/m2 (95% CI -0.53 to -0.08); waist WMD -0.31 in (95% CI -0.55 to -0.08; metric: -0.80 cm, -1.40 to -0.20)
   Certainty: Older synthesis largely overlapping with the 2024 one; dose and duration thresholds come from subgroup analyses.
   Obes Rev, 2017 · checked 2026-10-07 · we read the abstract
5. ev-flxw-05 · Meta-analysis or systematic review · systematic review and random-effects meta-analysis of trials · n = 16 trials, 1136 participants
   Meta-analysis of 16 trials with 1136 participants indicated significant improvements in weight (SMD: 0.81; 95 % CI: 1.54 to -0.09, p = 0.028; I2 = 88.7 %, p < 0.001), waist circumference (SMD: 1.54; 95 % CI: 2.77 to -0.31, p = 0.002; I2 = 85.3 %, p < 0.001), and triglyceride (SMD: 0.56; 95 % CI: 1.02 to -0.10, p = 0.016; I2 = 87.4 %, p < 0.001), but not BMI (SMD: 0.63; 95 % CI: 1.28 to 0.02, p = 0.058; I2 = 87.9 %, p = 0.005)
   
   Who: patients with type 2 diabetes
   Effect: weight SMD 0.81 (95% CI 1.54 to -0.09 as printed), p = 0.028; waist SMD 1.54, p = 0.002; BMI SMD 0.63, p = 0.058; I2 85-89%
   Certainty: Standardized differences with very high heterogeneity; signs in the abstract are printed without minus, kilograms not given.
   Diabetes Metab Syndr, 2025 · checked 2026-10-07 · we read the abstract
6. ev-flxw-06 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 5 trials
   There was no significant effect of flaxseed supplementation on weight (WMD = −0.05 kg; 95% CI: −0.39, 0.28, p = .75; I 2 = 0.0%) and BMI (WMD = 0.01 kg/m2; 95% CI: −0.11, 0.12, p = .88; I 2 = 0.0%) according to the pooled results using the random‐effects model from five trials in patients with CAD (Figure 3F,G).
   
   Who: patients with coronary artery disease, trials lasting 10 to 24 weeks
   Effect: weight WMD -0.11 lb (95% CI -0.86 to 0.62; metric: -0.05 kg, -0.39 to 0.28), p = .75; BMI WMD 0.01 kg/m2 (95% CI -0.11 to 0.12), I2 0%
   Certainty: Few trials; weight was not the primary aim in this population.
   Clin Cardiol, 2024 · checked 2026-10-07 · we read the fulltext
7. ev-flxw-07 · Randomized controlled trial(s) · randomized controlled trial, lifestyle advice control (no placebo) · n = 50
   Participants were randomly assigned to take lifestyle advice or lifestyle advice plus 30 g/day milled flaxseed for 12 weeks. The primary outcome was body weight; secondary outcomes included other anthropometric parameters, lipid profile and inflammatory biomarkers. Results: At the end of the study, the following significant mean differences were seen in flaxseed and control groups, respectively: weight [-9.36 vs. -3.09 kg; P < 0.001], BMI [-3.34 vs. -1.2 kg/m2; P < 0.001]
   
   Who: overweight and obese adults, BMI 30.72 ± 3.31 kg/m2, 12 weeks
   Effect: weight -21 vs -6.8 lb (-9.36 vs -3.09 kg) (P < 0.001); BMI -3.34 vs -1.2 kg/m2
   Certainty: Small, unblinded, no placebo; the 13 lb (6 kg) difference is far above the pooled average and likely inflated.
   Int J Vitam Nutr Res, 2022 · checked 2026-10-07 · we read the abstract
8. ev-flxw-08 · Randomized controlled trial(s) · double-blind randomized placebo-controlled bi-center trial · n = 108
   At the end of the 12-week study, body weight reduction was greater in the 104HD group (4.96 ± 1.89 kg, p < 0.001 vs. placebo) and 104LD group (3.70 ± 2.57 kg, p < 0.001 vs. placebo) compared to the placebo group (1.33 ± 2.05 kg).
   
   Who: overweight and moderately obese adults, BMI 25 to under 35, hypocaloric diet, 12 weeks
   Effect: weight loss 4.96 ± 1.89 kg (high dose) and 3.70 ± 2.57 kg (low dose) vs 1.33 ± 2.05 kg placebo; at least 5% loss in 68% and 46% vs 9%
   Certainty: Proprietary mucilage fiber extract (IQP-LU-104), not whole seed; single trial.
   Obes Facts, 2022 · checked 2026-10-07 · we read the abstract
9. ev-flxw-09 · Randomized controlled trial(s) · double-blind randomized placebo-controlled bi-center trial · n = 108
   Respiratory tract infections and gastrointestinal symptoms were the main adverse events reported and none of the adverse events were related to the intake of IQP-LU-104.
   
   Who: overweight and moderately obese adults, 12 weeks
   Effect: main adverse events respiratory tract infections and gastrointestinal symptoms; none related to IQP-LU-104
   Certainty: Short trial of an extract; tolerance of 30 g or more of whole seed (bloating, need for fluid) not assessed here.
   Obes Facts, 2022 · checked 2026-10-07 · we read the abstract
10. ev-flxw-10 · Randomized controlled trial(s) · randomized controlled trial · n = 70 enrolled, 64 analyzed
    However, we not observed any significant differences between two groups regarding the body weight, BMI, waist circumferences, systolic, and diastolic blood pressure (p > .05).
    
    Who: patients with mild-to-moderate ulcerative colitis, 30 g/day ground flaxseed, 12 weeks
    Effect: no significant difference in body weight, BMI or waist (p > .05); insulin and lipids improved
    Certainty: Population not selected for overweight; weight was a secondary outcome.
    Phytother Res, 2021 · checked 2026-10-07 · we read the abstract
11. ev-flxw-11 · Randomized controlled trial(s) · triple-blind randomized placebo-controlled trial · n = 112
    BMI decreased by 0.86 units compared to 0.06 units in the placebo group.
    
    Who: patients with hypertension aged 35 to 70, 10 g or 30 g flaxseed or placebo, 12 weeks
    Effect: BMI -0.86 (30 g group) vs -0.06 (placebo)
    Certainty: BMI change under 1 unit; the 10 g dose results not given for BMI in the abstract.
    Explore (NY), 2022 · checked 2026-10-07 · we read the abstract
12. flx-c1-08 · Randomized controlled trial(s) · randomized controlled dose-ranging trial · n = 34
    Plasma ALA concentrations increased with all flaxseed doses (P < 0.01), except the 20 g/day dose (P = 0.10), yet there was no significant dose-dependent response (P = 0.81). Only with the 30 g/day diet were n-3 polyunsaturated fatty acids (P = 0.007), and eicosapentaenoic acid (EPA) (P = 0.047) increased from baseline values. ... Flaxseed was well tolerated, even at the highest dose, as there were no reported adverse events, changes in cholesterol, platelet aggregation or urinary 11-dehydro-thromboxane B2.
    
    Who: 34 healthy adults aged 18 to 49, one muffin daily with 10, 20, 30 or 40 g milled flaxseed, 30 days
    Effect: plasma ALA up at 10, 30 and 40 g/day (P < 0.01), not at 20 g (P = 0.10), no dose-response; EPA up only at 30 g/day (P = 0.047); enterolignans up at all doses; no adverse events, no cholesterol change
    Certainty: 8 to 9 people per arm; 30 days; the missing effect at 20 g/day suggests noise rather than a true dose gap
    Eur J Nutr, 2016 · checked 2026-09-23 · we read the abstract
13. flx-c1-10 · Observational data · non-randomized controlled feeding study in healthy women with food chemistry analyses · n = —
    Flaxseed raised alpha-linolenic acid and long-chain n-3 fatty acids in both plasma and erythrocyte lipids, as well as raising urinary thiocyanate excretion 2.2-fold. Flaxseed also lowered serum total cholesterol by 9% and low-density-lipoprotein-cholesterol by 18%. ... Cyanogenic glycosides (linamarin, linustatin, neolinustatin) were highest in extracted flaxseed mucilage but were not detected in baked muffins containing 150 g flaxseed/kg.
    
    Who: healthy women eating 1.8 oz (50 g) raw ground flaxseed a day (12 to 13 percent of energy) for 4 weeks; test meals and baked muffins analyzed
    Effect: urinary thiocyanate 2.2-fold; total cholesterol -9%, LDL -18%; postprandial glucose -27% with 50 g carbohydrate from flaxseed or 25 g mucilage; cyanogenic glycosides highest in extracted mucilage, not detected in baked muffins
    Certainty: 1993 single-group feeding study, no randomized control, sample size not in the abstract; thiocyanate rise shows cyanide exposure at 50 g/day raw seed even though the authors judged it safe
    Br J Nutr, 1993 · checked 2026-09-23 · we read the abstract
14. flx-c1-11 · Randomized controlled trial(s) · randomized double-blind crossover clinical trial · n = 80
    The percentage of flaxseed supplemented test food out of total dietary intake was 20% of energy. ... No significant changes were observed in the basic laboratory values or in blood lipids. There was a significant increase in serum alpha-linolenic acid, eicosapentaenoic acid and docosapentaenoic acid. Serum enterolactone concentration was doubled during flaxseed supplementation. Serum thiocyanate and blood cadmium values did not exceed reference values and there was no difference between the diets.
    
    Who: 80 volunteers, double-blind crossover, meals with 1.3 g/100 g ground flaxseed and 5 g/100 g flaxseed oil for 4 weeks against unsupplemented foods, 4-week washout
    Effect: no change in basic laboratory values or blood lipids; serum ALA, EPA and DPA up; enterolactone doubled; thiocyanate and cadmium within reference and no difference between diets
    Certainty: the flaxseed dose is expressed per 3.5 oz (100 g) of food rather than grams per day; sponsor was a national technology agency; lipids did not change
    Eur J Clin Nutr, 2002 · checked 2026-09-23 · we read the abstract
15. flx-c1-13 · Observational data · structured literature review of documented interactions and contraindications · n = 1491 pairs
    While 85 primary literatures, six books and two web sites were reviewed for a total of 1,491 unique pairs of HDS-drug interactions, 213 HDS entities and 509 medications were involved. ... Of the 152 identified HDS contraindications, the most frequent involved gastrointestinal (16.4%), neurological (14.5%), and renal/genitourinary diseases (12.5%). Flaxseed, echinacea, and yohimbe had the largest number of documented contraindications.
    
    Who: 85 primary papers, six books and two websites covering 213 supplement entities and 509 medications
    Effect: flaxseed among the three entities with most documented contraindications; the most frequent contraindication categories were gastrointestinal (16.4%), neurological (14.5%) and renal or genitourinary (12.5%)
    Certainty: a count of documentation, not of clinical events; the abstract does not say which conditions flaxseed is contraindicated for; our drug-label layer has no flaxseed row
    Int J Clin Pract, 2012 · checked 2026-09-23 · we read the abstract
16. flx-c1-16 · Position of an expert body · European Commission regulation, recital and annex · n = —
    When ground linseed as such is consumed, the bioavailability of hydrocyanic acid and human exposure levels to it are higher than when whole linseeds are consumed or when they are heat-treated.
    
    Who: linseed placed on the EU market, including ground, milled, cracked and chopped seed sold to consumers
    Effect: Regulation (EU) 2022/1364 amends the contaminant limits for hydrocyanic acid in linseed (Annex rows 8.3.1 and 8.3.2) and exempts small consumer packs labeled Only to be used for cooking and baking. Do not consume raw!; the numeric mg/kg limits did not render in our fetch
    Certainty: a legal limit reflects the regulator's exposure assessment (EFSA ARfD 20 microgram cyanide per kg body weight), not a trial; the sentence was confirmed on the page by two independent fetches but the numeric limits could not be read from the table rendering
    Commission Regulation (EU) 2022/1364, Official Journal, 2022 · checked 2026-09-23 · we read the section