One of my foodie friends has entered menopause with great gusto. My friends and I have been treated to endless, dramatic and sometimes hilarious accounts of her escapades as a woman on the verge (her words, not mine).
More recently she has started carrying around a bag of flaxseed in order to smother all of her food when dining out. She claims that flaxseed has cured her hot flashes (and she has tried everything).
As she is quite evangelical about flaxseed, the rest of us are a bit scared to ask her about the evidence behind this. As mentioned she is quite dramatic and may well be susceptible to a little ‘white magic’ or the 'placebo effect' as it is more commonly caused.
In many ways, you could argue that what matters is the fact that she is getting good symptomatic relief and I should leave it at that.
However, as a diehard investigator, I have to know if there is a grain (or seed) of truth in the claims that flaxseed relieves menopausal symptoms (or anything else for that matter).
What Is Flaxseed?
Flax (Linum usitatissimum L.) is a blue flowering herb that grows well in the northern hemisphere and is an oil seed crop.
Flax can be divided into two main parts:
- the stem which is a rich source of fiber and
- small, brown, oval-shaped edible nutty seeds (flaxseeds).
Flaxseed is also commonly called linseed. Technically speaking, flaxseed is the term used when flax is used as food while linseed is more commonly used for industrial applications of this plant.
There are two main types of flax:
- brown flax which grows in warm humid climates and
- golden flax which prefers to grow in colder climates.
Flax has been cultivated for at least 5000 years. The French King, Charlemagne, was a raving fan of flaxseed (presumably he was not menopausal) and even passed a law requiring that all of his subjects take flaxseed.
From an economical perspective, flaxseed is an important crop. Canada is currently the worlds largest producer and exporter of flaxseed, while India has the highest acreage of flaxseed worldwide.
Fiber derived from flax is cultivated for linen (although technically speaking we should say that fiber comes from linseed).
From a nutritional perspective, flaxseeds are a source of:
- alpha lipoic acid (22% of flaxseed) which in turn is a source of omega-3
- lignans (secoisolariciresinol diglucoside) which are a rich source of phytoestrogens and
- Fiber (28% by weight).
A closer look at the typical content of flaxseed shows that 100 gm contains:
- Protein 20.3 g
- Fat 37.1 g
- Minerals 2.4 g
- Fibre 24.8 g
- Carbohydrate 28.9 g
- Energy 530 kcal
- Iron 2.7 mg
- Vitamin A 30 microgm
- Vitamin E 0.6 mg
- Thiamine 0.23 mg
- Riboflavin 0.07 mg
- Niacin 1 mg
- Pyridoxine 0.61 mg
- Folic Acid 112 micrograms.
There are two interesting things about the nutritional content of flaxseed that are worth mentioning here.
Firstly, flaxseeds are a source of alphalipoic acid (ALA) which in turn is a source of long chain omega-3 (EPA and DHA). Omega-3 enriched eggs come from chickens that are fed a diet high in flaxseed.
However, it should be noted that the conversion of ALA to EPA and DHA from flaxseeds is inefficient and is especially poor in people with a diet rich in omega-6 such as vegetable oils and processed foods. This means that flaxseed is far from a perfect source of omega-3.
Secondly, whole flaxseeds pass through the digestive system undigested. The best way to eat flaxseeds is to grind a few days supply at a time in a coffee grinder. That way you get the benefit of the whole seed. The science behind this is nicely explained in the New York Times bestselling book 'The Plant Paradox'.
Essentially, the main function of plant seeds is to produce new plants and not to feed humankind.
There are two types of seeds:
One type is ingested by animals and birds who travel away from the parent plant and pass out whole seeds in their feces which means that the parent plant does not compete with the offspring for nutrients.
One type falls from the parent plant and sprouts close by.
Flaxseeds are designed to be eaten whole and trafficked by birds and animals to new locations which means that they are resistant to degradation in the gastrointestinal tract. Hence the need to grind or de-hull them.
There is an actual Flax Council which reports that over 300 new flax products are launched each year in the US and Canada.
There are over 1000 flaxseed products for sale on Amazon ranging from seeds to oil to powder to flour capsules. A 1200 mg capsule of flaxseed costs less than $0.20.
I have to wonder why my friend does not just take a few flaxseed capsules as opposed to hauling around a giant bag of flaxseed but maybe the magic is in the ceremony and not the seed?
Is There Any Research?
There are 2933 publications on flaxseed which includes 220 clinical trials. Let's compare this to the number of studies on omega-3. There are over 10 times more publications and clinical trials on omega-3 as compared to flaxseed. Alternatively, we could compare to chia seeds, which boast only 9 clinical trials at the time of writing.
I know that I just said that flaxseed is a source of omega-3 but for the purposes of this article, I am going to focus on studies on flaxseed. I am not going to join the dots or extrapolate eg if flaxseed is a source of omega-3 and if omega-3 does this, then flaxseed should do this too.
Nope, I am sticking to the facts that we have about flaxseed itself.
Does Flaxseed Help with Weight Loss?
A 2017 systematic review and meta-analysis crunched data from 45 randomized trials to assess the effect of flaxseed on body weight and body composition (5). The study was carried out by research collaboration with contributors from Iran and Canada.
The meta-analysis had a clear and simple conclusion; it showed that supplementation with flaxseed resulted in a significant reduction in body weight and waist circumference. Sub-group analysis suggested optimal outcomes were seen with doses of >/= 30g/day, >/= 12 weeks of supplementation and patients with a high baseline BMI.
The study authors concluded that 'Whole flaxseed is a good choice for weight management particularly for weight reduction in overweight and obese participants'.
Do Flaxseed Helps Make Skin and Hair Healthy?
There is really only one study that addresses the question of flaxseed and skin (6). This small German study showed that flaxseed can improve skin quality in women (though as you will see I don't fully agree with the conclusions).
This study had three arms:
- flaxseed as a source of alpha-linoleic acid and linoleic acid
- borage oil as a source of linoleic and gamma-linoleic acid and a
- a control group who received medium-chain fatty acids.
Skin irritation was induced in these women with a nicotinate treatment.
Both of the intervention arms had significantly less skin reddening and water loss as compared to the control arm. There was no difference in hydration between the arms of the study.
Personally speaking (as I don’t deliberately irritate my skin with nicotinamide every day), I am more interested in the hydration results. Hence, I consider this to be a negative outcome study.
Then there was a study that looked at the effect of flaxseed supplementation in 6 horses who had ‘sweet itch’ (7). Apparently, this is a common skin condition in horses and is due to an allergic reaction to bites from midges. Not only can horses develop annoying skin rash and itch, but they can also self-mutilate in an effort to scratch that itch.
In this study, six horses received flaxseed supplementation for 42 days. This was a before and after type study design where each horse acted as its own control. The results of the study showed that flaxseed supplementation reduced the skin reaction to midges bites.
Also, the horses had a significant decrease in long-chain fatty acids (behenic acid and lignoceric acid) in their hair. Again here we see benefits in terms of reducing skin irritation but not evidence of helping promote skin appearance, hydration or wrinkles (the things that women like me would want to buy in a jar).
I have no idea what to make of the changes in the fat content of the horse's hair and the authors don't comment on whether the horse looked more glossy or shiny.
There is very little published data on flax for hair and skin and the available information certainly does not support a role of flax as a general cosmaceutical.
Does Flaxseed Decrease Menopausal and Hormonal Imbalance Symptoms?
There are plenty of menopausal women (like my foodie friend) who are looking for effective, safe and natural alternatives to hormone replacement therapy.
A 2013 systematic review evaluated flax interventions for the improvement of menopausal symptoms and post-menopausal bone health (8).
The researchers initially found 64 relevant studies but eliminated 53 studies because they included flaxseed along with other treatments which would have made it difficult to isolate out the effects of flaxseed alone. They found 10 studies that looked at the severity of menopausal symptoms but found no significant benefit of flaxseed on these symptoms or circulating sex hormones.
Flaxseed consumption did result in a significant increase in the ratio of urinary -hydroxyestrone/16-hydroxyestrone which has been shown to be protective against breast cancer. These studies did not follow the women to see if this actually panned out into actual clinical benefits and therefore remains just a nice theory for now.
There was too little information on bone health to draw any meaningful conclusions. The take-home message was that flax is not currently indicated for the alleviation of menopausal symptoms.
In order to do justice to the issue of flaxseed for menopausal symptoms, let’s take a closer look at one of the clinical trials.
A 2010 study from Brazil enrolled 38 post-menopausal women in a study where they were randomized to either 2 slices of bread containing 25g of flaxseed or wheat bran per day (9). The study ran for 12 weeks. All patients finished the study (it is pretty unusual to have no dropout rate in a study, so kudos to the study team).
Both arms of the study had significant but similar reductions in hot flashes and menopausal symptoms. What does this mean? This means that flaxseed is not more effective than placebo at reducing hot flashes.
A 2016 Iranian systematic review looked at flaxseed and Hypericum perforatum on hot flashes, estrogen-dependent cancers and vaginal atrophy (10). This paper was quite confusing. In the methods section, the authors state that ‘flaxseed showed beneficial effects on hot flash frequency and intensity which was not statistically significant’.
However, seven lines later, in the conclusion section the authors state that ‘the results of our systematic review suggest a beneficial effect on vasomotor symptoms with both flaxseed and Hypericum perforatum."
Finally, a 2102 study found no benefit of flaxseed for menopausal hot flash symptoms in 188 women from 22 sites (11). There was a reduction of 4.9 in the hot flash score in the flaxseed arm as compared to a 3.5 score reduction in the placebo arm. This difference is not statistically significant.
There is no science to support a role for flaxseed for menopausal symptoms. Some women who received both placebo and flaxseed reported improvements in menopausal symptoms.
Do Flaxseeds Support Digestive Health?
Flaxseed was described as a laxative by Hippocrates way back in 500 BC. This makes sense as we know that flaxseeds are a source of fiber. What (if anything) do we know beyond that?
A 2012 British study compared the pilot study compared the clinical effectiveness of (i) whole linseeds versus ground linseeds; (ii) whole linseeds versus no linseeds; and (iii) ground linseeds versus no linseeds in the management of irritable bowel symptoms (12).
The study was randomized but not blinded and involved 40 patients over a time period of 4 weeks. There were no significant changes in stool frequency or stool consistency for any of the groups and no statistically significant difference between the three arms of the study.
Despite this, the authors conclude that 'linseeds may be useful in the relief of irritable bowel symptoms'. I am not sure how they reached this conclusion as this is not what their own research showed.
Beyond that, there is a study in mice who were given acetic acid to cause inflammatory bowel disease and then given flaxseed to try to cure the ulcerative colitis (13). The study looked at a bewildering array of cytokines and declared that flaxseed had beneficial effects on IFN-γ and TNF-α and increasing IL-17, which was deemed a good thing.
There is no direct human clinical research evidence that flaxseed is good for digestive health.
Do Flaxseeds Lower Cholesterol and Treat Hyperlipidemia?
An Iranian study compared the effect of 30 g of raw flaxseed powder to placebo every day for 40 days in 70 patients with hyperlipidemia (14). The study showed that the flaxseed intervention was effective at significantly reducing cholesterol and hyperlipidemia as compared to the control arm of the study.
The cardiovascular clinical implications of flaxseed supplementation were reviewed in 2009 and the author concluded that the data shows that flax lignans but not flaxseed oil slows the progression of atherosclerosis (15).
Flaxseed (flax lignans) does lower cholesterol and lipids in people with hyperlipidemia and also slows the progression of atherosclerosis.
Do Flaxseed Help Prevent Cancer?
The majority of data on flaxseed and cancer relates to breast and prostate cancer.
It is generally agreed in the complementary/alternative medicine community that the level of evidence needed before intervention should be recommended should be directly proportional to the risk/severity of the disease.
Using that logic, cancer interventions need significant data in order to be considered.
In clinical research, we use a hierarchy for the evaluation of research and rank the value of the research from lowest to highest as follows:
- theoretical research ie this compound should logically work
- laboratory data ie animal data or experimental cell lines
- observational studies
- clinical trials, and then
- meta-analysis and systematic review of high-quality clinical trials.
Let's see if we can find a meta-analysis to answer the question of cancer and flaxseed.
A 2018 Portuguese literature review took on the task of looking at flaxseed for breast cancer (16).
They reached the predictable conclusion that more studies are needed to answer the question (frustrating and not very helpful).
An older systematic review looked at the efficacy of flax in improving menopausal symptoms in women living with breast cancer and for potential impact on the risk of breast cancer incidence or recurrence (17). The authors of the study concluded that 'Current evidence suggests that flax may be associated with decreased risk of breast cancer.'
Flax demonstrates anti-proliferative effects in the breast tissue of women at risk of breast cancer and may protect against primary breast cancer. Mortality risk may also be reduced among those living with breast cancer'.
The big problem with this paper is the fact that it looked at so many variables that it is hard to really comment on the quality of the recommendations for breast cancer. Additionally, it focuses on menopausal women.
This means that we need to do our original research. We will follow the hierarchy of research as listed above.
Theoretically, flaxseeds contain phytoestrogen and could impact on breast cancer.
Next, let's look at laboratory bases studies and there are a number of studies that show that flaxseeds impact positively on breast cancer in laboratory animals (18).
The next level of research involves observational studies. A Canadian study looked at data from 6369 women who took part in the Ontario Women's Diet and Health Study and found that flaxseed intake is associated with a reduction in breast cancer risk (19).
On the plus side, this was a really well-organized study with a large number of data points. On the negative side, it just observes things and does not actually study the effect of flaxseeds (which brings us to clinical trial data).
Another Canadian study looked at the effect of daily intake of either a 25 g flaxseed-containing muffin or a control (placebo) muffin in 32 menopausal patients with newly diagnosed breast cancer (20). They found a statistically significant reduction in the expression of certain tumor markers and a significant increase in cancer cell death.
The authors concluded that flaxseeds have the potential to reduce tumor growth in post-menopausal women with breast cancer. The study does not follow these women and this means that we can't say if the flaxseed resulted in meaningful clinical outcomes.
A 2012 study from the USA found that flaxseed supplementation in 147 men with prostate cancer resulted in higher urinary levels of lignans, reduced levels of Ki67 (a marker of cell growth) and lower levels of vascular endothelial growth factor (a compound which promotes the growth of blood vessels (21).
For Breast Cancer: There seems to be some beneficial effect of flaxseeds but it is hard to be more prescriptive than that at this time.
For Prostate Cancer: There is very limited but positive data on flaxseed. It must be emphasized that this data is based on tumor markers and not clinical outcomes.
Is Flaxseed Safe?
Flaxseed was given Generally Regarded as Safe status by the FDA in 2009 (22).
In the study of 188 menopausal women who received a flaxseed bar or a placebo bar for six weeks, no difference was noted in the side effect profile between the two arms of the study except for skin itch which was more common in the placebo arm of the study (11).
That being said, It is best to avoid flaxseed during pregnancy and while breastfeeding as they contain hormones.
As noted by Hippocrates, flaxseed can cause diarrhea. Considering the high fiber content of flaxseed, it is important to drink lots of water while eating flaxseeds.
Many nutritionists do not recommend flaxseed oil as it goes rancid quickly and lacks the lignans present in the whole flaxseeds. The rancid oil contains oxidized fats which are toxic.
Overall, flaxseeds seem to be well-tolerated and a good food choice as part of a balanced, healthy diet.
There is limited data to support a role for flaxseed in cardiovascular health but it is not clear if flaxseeds are any better for heart health as compared to other sources of omega-3 or fiber.
Flaxseeds may have a role to play in some hormone-related cancers but there is too little data to more prescriptive than this at the moment.
As regards my foodie friend - there is no evidence to support recommending flaxseeds for menopausal symptoms. However, the studies show that women in both the flaxseed treatment arm and the placebo arm reported symptom improvement.
She is one of those women. I have no intention of disillusioning my dear friend and plan to allow her to enjoy the benefits of her flaxseeds.
On the other hand, I have no intention of recommending them to any of my friends or patients for menopausal symptoms either.