There is one consistent theme on social media when it comes to nutrition and fertility and that is that Flaxseeds and Peas are a no go for fertility, often these statements are made without relevant studies so let's look into it further by starting with Flaxseeds which are also known as Linseeds. It's important that I note that this blog is neither for or against the feeding of peas or flaxseeds to breeding dogs, it is simply a look at the available information to help dog owners make informed decisions. We welcome your feedback if you come across a study or reputable source of information we may have missed. Starting with 'Phytoestrogens' is a good place, "These plant oestrogens which are are substances that occur naturally in plants. They have a similar chemical structure to our own body's oestrogen (one of the main female hormones) and are able to bind to the same receptors that our own oestrogen does. Phytoestrogens behave differently to female oestrogen and this depends on the oestrogen's environment (whether a woman is in her reproductive years and has higher oestrogen, or is postmenopausal with lower oestrogen), how they bind to the oestrogen receptor and particularly to which oestrogen receptor they bind to. Eating phytoestrogens can produce either some of the same effects as human oestrogen (oestrogenic effects) or opposed effects (anti-oestrogenic effects). Which effects are triggered depends on existing levels of oestrogen in the body and how the phytoestrogens bind to receptors in the body.
Some Key Points on Phytoestrogens in humans:
The effect of phytoestrogens on menopausal hot flushes varies between individuals, as only a third to a half of on individuals have the gut bacteria that convert the phytoestrogens to a more potent form
There is growing evidence to suggest that phytoestrogens may help with bone and cardiovascular health, but this remains unclear.
It is not recommended that woman at high risk of breast cancer, or who have had breast cancer, take soy supplements
Different types of phytoestrogen include:
Isoflavones (found in soy and other legumes such as chickpeas, mung beans and alfalfa)
Coumestans (found in alfalfa and clover sprouts, and sprouted Legumes such as mung beans and soy sprouts)
Lignans (found in linseed, grains and vegetables)
Foods containing phytoestrogens:
Whole soybean soy milk
SEEDS & NUTS
Red Kidney Beans
Cancer & Phytoestrogens:
There has been much speculation about the risk of breast cancer from phytoestrogens in soy products. This is mainly based on the misconception that because these foods contain oestrogen-like compounds, they might stimulate breast tissue in the same way that our own body's oestrogen or pharmaceutical oestrogen can.
A 2006 review of research on the link between phytoestrogens and breast cancer showed that:
There is a small reduction in the risk of breast cancer associated with phytoestrogen consumption
The risk of breast cancer was reduced more in premenopausal women who consumed soy compared to postmenopausal wome.
A diet high in phytoestrogen in early life (before puberty) may be important for the anti-cancer effects of phytoestrogens in later life.
There is conflicting data on the breast cancer risk of individual isoflavones, daidzein and genistein, that are found in soy. For this reason, supplements containing individual soy isoflavones, and soy supplements which have standardised amounts of these constituents should be avoided. Eating whole soy foods is safer.
A 2013 review highlights that studies that show that eating soy decreases the risk of developing breast cancer, are done in Asian rather than Western cultures. This is likely attributed to the greater amount of soy consumed in Asian diets compared to Western diets. In a typical Asian diet, the average daily intake of isoflavones is 25-50mg, whereas in Western diets the amount of soy isoflavones is less than 1mg per day!
The bottom line with eating soy is that eating a diet with the amount of soy isoflavones typical of an Asian diet seems to be protective against breast cancer and it is these amounts that are needed for symptom relief.
How much soy contains 50mg of isoflavones? 50mg of soy isoflavones =
About 200g tofu
About 100-150g of tempeh
About three cups of whole bean soy milk
About 100g of cooked/canned soybeans
It's important to start with the fact that there have been no studies in the dog to verify whether or not flaxseed causes infertility.
From my understanding, the concern is the lignon portion of flaxseed can act as a moderate anti-estrogen agent and therefore, might affect reproduction in the female.
So let's see what Science says...
There is a 2009 rodent study(1) on 'Genistein' which is based around Soy isoflavones which looks into cycles and reproduction however given Soy isn't common in dog food, I'm not sure how relevant that may be. The study showed that eggs from mice treated neonatally with genistein had normal morphology (normal meiotic spindles) and fertilised equally as well as eggs from control mice suggesting the major contributor of infertility in these mice is not egg quality. One caveat is that these studies were done in young mice (2 months of age) and it is not known if the quality of the eggs decreases later in life.
A 1997 study(6) titled 'Effect of feeding rolled flaxseed on milk fatty acid profiles and reproductive performance of dairy cows' found that feeding FLX at 0.85 kg/cow per day (DM basis) altered the fatty acid profile of milk, but milk yield, milk composition, and reproductive performance of dairy cows were not affected.
Then we have a 2015 study(8) titled 'Milk yield and reproductive performance of dairy heifers and cows supplemented with polyunsaturated fatty acids' - this study was based around extruded linseed (Flaxseed) and soybean as sources of polyunsaturated fatty acids. Supplementation had a positive effect on profitability, with significant increases in milk yield in supplemented cows, but not in heifers. Treatments had no effect on milk fat content, but higher milk protein contents were observed with supplementation. A higher conception rate was found for supplemented heifers, but not for cows. Fat sources containing PUFAs are recommended for dairy cattle supplementation, since they improve fertility in heifers and milk yield in cows.
On a slight different reproductive topic is a 2006 study(9) titled 'Lower Pregnancy Losses in Lactating Dairy Cows Fed a Diet Enriched in α-Linolenic Acid'. The objectives were to determine if a diet enriched in α-linolenic acid (ALA) would influence ovarian function, early embryo survival, conception rates, and pregnancy losses in lactating dairy cows. Flaxseed and Sunflower seeds were used in this study. They found that pregnancy losses were lower in cows fed FLAX (9.8%) compared with those fed SUNF (27.3%). Including flaxseed in the ration of dairy cows increased the size of the ovulatory follicle and reduced pregnancy losses.
Let's look at a different animal, 'Sheep', a 2012 study(7) titled 'Effects of diets enriched in different sources of fatty acids on reproductive performance of Zel sheep' found that there was no difference in reproductive indices, including: fertility rates, prolificacy and sex ratio of lambs among groups. In conclusion, diets enriched in n-6 and n-3 polyunsaturated fatty acid prior to mating did not affect reproductive performance, insulin, IGF-1 and progesterone in Zel sheep.
From what I can gather from studies is that at this time Flaxseed doesn't negatively affect reproduction, however, no canine-specific studies have been done. If you come across one, be sure to let us know!
What about Peas?
When conducting a search online for why Peas are adverse to fertility I came across this statement: "There is a natural chemical in peas known as m-xylohydroquinone that may keep you from getting pregnant. Research on peas goes back as far as the 1950s. There is even research ongoing about how peas could be used as a natural contraceptive.&q