article
by Dr Harriet Holme18 Sep 2020
More than 80% of couples will conceive within a year of trying. A couple may be considered to have fertility concerns (or sub-fertile) if they have been trying to conceive for over a year with no success (1). After this time, it is a good idea to speak with your doctor. If you are a woman over the age of 36 years, or have known fertility concerns, you should see your doctor sooner. Difficulty conceiving may affect between 10-25% of all couples who are trying to have a baby (1,2). Subfertility factors are split pretty evenly between men and women (1,2).
Human semen quality has declined worldwide in the last 40 years by up to 50%, having a significant impact on fertility (3). This thought to be due in part to modifiable lifestyle factors such as lifestyle, unhealthy diets and pollution (3).
Male factor infertility can be caused by a number of reasons, ranging from structural problems, hormonal levels, genetics, and medications. Unfortunately, not all causes of abnormal sperm production have an identifiable underlying cause. Overall, up to 25% of cases of male infertility have no identifying cause, with all investigations within the normal range.
At this undeniably stressful time, couples naturally look to improve their fertility with diet. I’ll explore in this article if that is possible, what the evidence is for different diets, what foods to avoid and supplements that may support your fertility.
Carbohydrates
Both the quality and quantity of dietary carbohydrates can influence glucose homeostasis and insulin sensitivity, which may influence ovarian function (4). Reduction in dietary carbohydrates among women with polycystic ovary syndrome (PCOS) has been shown to also improve insulin sensitivity, decrease testosterone levels, and potentially enhance ovulation (4). However, carbohydrate intake in healthy women, has not been found to modify these hormones (4).
Whole grains have antioxidant, and anti-inflammatory properties, in addition to beneficial effects on glucose metabolism. One study (EARTH study) showed that a higher level of whole grains in the pre-conception diet, was associated with a higher probability of live birth (5).
Dairy and Soy
Studies on mice, replicated in humans have suggested that dairy might increase the rate of ovarian aging, but no association between overall fertility has been found (4). Looking at women undergoing assisted reproduction technologies (ART), again no association between dairy consumption and pregnancy was found (4). While there has been previous concerns about soy, there is no robust evidence of negative effects on fertility (6).
Meat and Fish
Blastocyst (the stage after an egg has been fertilised, before it becomes an embryo) formation was decreased among women consuming more red meat, while increased by higher fish consumption (4). These findings have led to widespread guidance to eat two servings of fish per week, avoiding larger fish (swordfish, bigeye tuna) that have highest levels of contamination with mercury.
In men, there is mixed evidence of any negative effect of meat consumption (6). Although a number of studies did find that eating processed meat was associated with poorer sperm quality, and given that processed meat is associated with increased risk of long term cancer, it seems sensible to avoid it (6).
Omega 3 and 6 Fatty Acids
Omega fatty acids are called essential, as your body is unable to manufacture them, so they must be included in your diet. Omega 3 and 6 fatty acids play an important role in the production of sperm. Omega fatty acids are used for energy during oocyte (egg) maturation and early embryo development (4). They also are chemical precursors for a number of important hormones, that play a vital role in implantation and the maintenance of pregnancy.
Mouse studies have found that omega 3 supplementation delayed ovarian aging, and one study has replicated this in humans (4). The EARTH study found that for every 1% increase in serum long-chain omega 3 polyunsaturated fatty acid levels, the probability of clinical pregnancy and live birth increased by 8% (4).
Observational studies have found that a higher intake of omega 3 fatty acids was associated with a greater proportion of morphologically normal sperm (6). A trial of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) supplements (1.84g/d for 32 weeks) among 211 men with reduced number and motility of sperm found a significant increase in total sperm count and percentages of motile and morphologically normal sperm. Additionally, alpha-linolenic acid (ALA) and DHA were also associated with a positive outcome in women undergoing ICSI (7).
A systematic review of 16 studies found that 14 of the 16 studies found an improvement or association between both dietary omega 3 and supplementation, and at least one marker of semen quality (8). However, more research is required in order to fully clarify the effect.
Healthy men eating a traditional western-style diet, randomised to 75g/day of walnuts (high in omega 3 and 6) for 12 weeks, were found to have improved sperm vitality, motility and morphology compared with the control group (6). A prospective study found that men’s fish intake was related to shorter time to pregnancy and a lower risk of infertility (6).
There is considerable evidence suggesting that greater intake of omega 3 polyunsaturated fatty acids and lower intake of trans fats are associated with shorter time to pregnancy and better ART outcomes; the effect from other fatty acids (such as omega 6 fatty acids, saturated fats, and mono-unsaturated fats) on female fertility is less clear (4).
It’s not known if dietary omega fatty acids or supplementation have different effects on fertility, but given their importance for general health, it’s a good idea to incorporate them into your diet.
Sources of omega 3 fatty acids:
Sources of omega 6 fatty acids
Trans Fats
Trans fats are primarily found in commercially baked and fried foods and may accumulate in the testis. Trans fats have been banned in the USA, and companies in the UK signed up to a voluntary code to avoid them. However, as there is no need to declare them on the ingredients, it is not known if products still contain trans fats. Trans fatty acids and saturated fat appear to have an opposite effect to polyunsaturated fats (6). Intake of trans fats has consistently been related to poor semen quality and lower sperm counts (6). Trans fats have also been associated with increased risk of cancer, cardiovascular disease and diabetes, so are best to avoid altogether.
Mediterranean Diet
There is evidence of a beneficial effect of maternal Mediterranean diet with regard outcomes for ART (4). The Mediterranean style or similar diets have been consistently associated with better quality sperm and less DNA fragmentation (6). Greater adherence to healthy dietary patterns favouring whole grains, fish, fruits, vegetables, and olive oils, aligned with the framework of a healthy diet may not only improve overall health but improve fertility (3,4). Adherence to healthy dietary patterns is positively associated with sperm concentration and sperm motility (3).
A prospective observational study performed on 161 women found that a diet rich in fish, legumes, vegetables and low in carbohydrates was associated with a 40% increase in chance of pregnancy by intracytoplasmic sperm injection (ICSI) IVF (7). Conversely, there are studies that show no benefit of a Mediterranean style diet, but given the general health benefits, it is a good framework to follow.
Pesticides
Fruit and vegetables are universally recommended as an essential component of a healthy diet, but they do remain the greatest source of pesticide exposure for the general public (6). A study found that men who were ate the highest amount of fruit and vegetables associated with high pesticide residue (e.g. spinach, strawberries and apples), eating greater than 1 serving per day had a significantly lower (49%) total sperm count than men who ate less than 0.5 servings per day) (6). While eating even low to moderate pesticide residue fruit and vegetables was still associated with a higher percentage of abnormal sperm (6). While fruit and vegetables play a hugely important role in our diet, this study highlights the possible risk of pesticides. Therefore, while trying for a baby, it would be better to swap to organic produce to avoid possible risk from pesticides.
Weight
There is strong and consistent evidence that being overweight or obese plays a significant role in both male and female fertility (6). Time to conceive and increased rate of miscarriage are affected by female weight, with increasing time to conceive in those under weight (BMI <19) or over weight (BMI>25) (7). High BMI is also associated with complications of pregnancy such as gestational diabetes, hypertension and premature births (7). A healthy, balanced diet not only benefits your long-term health, but also helps sustain a long-term healthy weight.
Smoking
Smoking has significant effects on fertility, associated with a rapid decline in ovarian reserves, delayed time to pregnancy, increased risk of miscarriage, and lower success of ART (7). Similarly in males, smoking is associated with increased risk of motility and morphology problems with sperm (7).
Alcohol
A meta-analysis (grouped analysis) of 19 observational studies involving 98,657 women found that those who drank alcohol were more likely to have a lower rate of fertility (9). A dose response effect was seen, which means that as the quantity of alcohol consumption increased, it was associated with a greater reduction of fertility (9). Also, a systemic review of six epidemiological studies investigated a link between alcohol and fertility outcomes among women undergoing ART (10). Three of these studies found that alcohol consumption was associated with a decreased rate of fertilisation, embryo quality and implantation while undergoing ART (10).
Folic acid
Folic acid supplementation is recommended for all women trying for a baby and during the first 12 weeks of pregnancy, to reduce the risk of neural tube defects such as spina bifida. Pre-natal folic acid supplementation has also been shown to reduce ovulatory infertility and lead to a shorter time to pregnancy (4).
The effects of folic acid on male fertility are more mixed. A randomised controlled trial, of folic acid supplementation (15mg/d for 90 days) was associated with a 53% increase in sperm concentration and a doubling in the proportion of motile sperm (6). While a meta-analysis of six studies found that folic acid supplementation in men improved sperm concentration, but did not have a significant effect on motility or morphology (11). The same meta-analysis also concluded that combined folic acid and zinc supplementation improved sperm concentration and morphology but not motility (11).
Another randomised controlled trial looked at the effects of folic acid (5 mg/d for 182 days), or zinc, or folic acid and zinc, or placebo; sub-fertile men assigned to the folic acid and zinc arm had a 74% increase in total normal sperm count compared with pre intervention values and a 41% increase compared with post intervention values in the placebo arm, which did not reach statistical significance (6). It is difficult to interpret this result.
There is some evidence that supplementation with folic acid and B12, leads to a higher rate of pregnancy via IVF, but again more research is needed (12). NHS guidance is for preconception and conception supplementation of folic acid, and ensure your diet includes adequate B12 by eating meat, dairy, and eggs. If you are vegan then you should consider taking a supplement.
So, while folic acid does seem to play an important role in sperm production, quite how far this extends is uncertain. Given that folic acid is relatively safe, with few reported side effects, supplementation and a diet rich in folate are potentially worth a try.
Examples of foods rich in folate:
Myoinositol
Myoinositol is a carbohydrate that has an important role in signalling in the body. There is emerging evidence that myo-inositol may have a positive effect on sperm quality, but further research is needed (13).
Vitamin D
Vitamin D is known to have wide ranging effects on health. Recent systematic review findings on the role of vitamin D in fertility revealed evidence that vitamin D may have a positive impact on IVF outcomes such as improved pregnancy rate in females and semen quality in males(14).
Higher vitamin D levels have been associated with increased clinical pregnancy rate following IVF therapy in one study (15), while in another study more than two-thirds of infertile women were found to be vitamin D-deficient compared with the general population (16). In addition, vitamin D-deficient women were found to have significantly lower clinical pregnancy rates (17). However, other studies have not confirmed an association between vitamin D and IVF outcomes (18,19).
Collectively, these studies indicate that more robust clinical data is required to assess the effect of vitamin D in women undergoing IVF therapy
(14). Despite a negative effect of vitamin D deficiency on fertility rates, it is not clear if vitamin D supplementation in couples who have normal levels of vitamin D, is of benefit (4). However, in geographical locations where it is difficult to get enough sunshine to meet your vitamin D needs, such as the UK during autumn and winter months, it is still a good idea to supplement to prevent deficiency.
Omega 3
The importance of omega fatty acids both as whole foods and supplements is discussed above. It is important to avoid omega 3 supplements that are produced from liver or contain vitamin A as this is harmful during pregnancy.
Antioxidants
Previously, the most studied dietary micronutrient supplements in assisted reproductive techniques were found to be antioxidants that include vitamins A, B, C, D, E and coenzyme Q10 (20).
Vitamin E supplementation in both women and men has been shown to impact IVF outcomes, not only by reducing the time to achieve pregnancy in women, but also vitamin E administration in men has been found to improve sperm motility and reduce associated oxidative damage (12).
Studies have found a lower antioxidant level in the semen of infertile men (21). Supplementation of L-carnitine, selenium, vitamin C and vitamin E may lead to improved sperm concentration, motility, morphology and sometimes DNA integrity (21).
In males, antioxidants have been shown to reduce the number of reactive oxygen species, protecting semen from oxidative damage and improving sperm parameters such as motility (20) (22).
Between 25% to 87% of male subfertility is considered to be due to the effect of oxidative stress (2). Oral supplementation with antioxidants is thought to improve sperm quality by reducing oxidative damage (2). A Cochrane review found low-quality evidence from seven small randomised controlled trials that suggested that antioxidant supplementation in sub-fertile males may improve live birth rates for couples attending fertility clinics (2). Overall, there is no evidence of increased risk of miscarriage, however antioxidants may increase the chance of mild gastrointestinal upset but the evidence is of very low quality. More research is needed on the optimal dose of these supplements, and also if the benefits in sperm parameters, lead to an increased rate of pregnancy live births (21).
A Cochrane review looking at 50 trials, including 6510 sub-fertile women undergoing ART found that antioxidant supplementation increased pregnancy rate and number of live births (1). This suggests that among sub-fertile women with an expected live birth rate of 20%, the rate among women using antioxidants would be between 26% and 43% (1). Therefore, there is limited evidence in support of supplemental oral antioxidants for sub-fertile women, but unfortunately insufficient evidence to draw any conclusions about adverse events.
Overall, supplementary antioxidants have been found to improve semen quality, particularly motility, and may increase the probability of successful pregnancies. Evidence of a benefit in women is more mixed (6). Therefore, sub-fertile couples should be advised that overall, the current evidence is inconclusive based on serious risk of bias due to poor reporting of methods of randomisation, failure to report on the clinical outcomes live birth rate and clinical pregnancy, often unclear or even high attrition, and small overall sample sizes. Further large well-designed randomised placebo-controlled trials reporting on pregnancy and live births are still required to clarify the exact role of antioxidants.
Combinations
A number of different combinations of nutrients have been trialled. Some of these combined effects support those seen in isolation.
Supplementary intake of selenium and zinc, omega-3 fatty acids, Coenzyme Q10 (CoQ10) and carnitine have been positively associated with sperm quality (3).
A meta-analysis analysed 15 studies, totalling 2900 participants reported the following findings (23):
Vitamin D, vitamin E, CoQ10, and L-carnitine together have shown improvements in live birth rates (24).
A meta-analysis of seven randomised controlled double-blind placebo controlled trials found that selenium (200mcg/day and 100mcg/day) improved sperm concentration and motility; L-carnitine (2g/day) and acetyl-l-carnitine (1g/day) improved motility; co-enzyme Q10 (200 and 300mg/day) improved motility and morphology (25).
There is evidence to support that zinc and selenium levels may be lower in couples undergoing IVF, and that supplementation may help, but more evidence is needed (6,12).
Therefore, try to ensure your diet has lots of zinc and selenium in it. Foods rich in:
Aim to eat a whole food diet, similar to a Mediterranean style diet, full of good quality carbohydrates that are less likely to contribute to insulin resistance. Not only does a healthy diet reduce risk of other long-term disease, but also helps maintain a healthy weight, which is important with regards fertility.
Try to avoid processed meat, but the evidence does not suggest that you need to avoid other types of meat, dairy or soya. Eat more healthy polyunsaturated oils such as extra virgin olive oil, and omega fatty acids by trying to have fish twice a week.
Eat a handful of nuts a day, and regularly choose walnuts that are high in omega fatty acids. More research is needed to determine if a diet rich in omega 3 is as beneficial as supplementation. However, given the importance of omega 3 in our diet and the beneficial effects on long term health, regular intake is important.
Avoid trans fats, alcohol and smoking. Both partners should aim for a healthy weight as both underweight and overweight are associated with decreased fertility.
Folic acid supplementation decreases the risk of neural tube defects and is associated with a shorter time to pregnancy and increased concentration of sperm. Therefore, it seems reasonable for men to have a folic acid rich diet, and trial folic acid supplementation, given there are no significant side effects reported and it is safe for women to take during pregnancy. While there might not be strong evidence of benefit of vitamin D if you have normal levels, it’s advisable to ensure your vitamin D levels are sufficient.
Supplementary antioxidants have been found to improve semen quality, particularly motility, and may increase the probability of successful pregnancies. Evidence of a benefit in women is more mixed (6). Further studies are needed to clarify the exact role of antioxidants in females, but in males they appear to be relatively safe (2). There are also lots of ways of increasing your antioxidant intake in your diet.
Enjoy:
Avoid:
Supplement:
Article Credit: Dr Harriet Holme (https://healthyeatingdr.com/)
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