Optimising fertility with nutrition: Advice for both women and men

Infertility – a failure to achieve pregnancy after 12 months of unprotected and routine sexual intercourse – affects many reproductive-aged couples attempting pregnancy.

A growing body of evidence points to a link between diet and fertility for both females and males. It seems that negative lifestyle factors such as smoking, excessive caffeine intake and high BMI can significantly reduce fertility and reproduction. In addition, research shows that the nutritional status of both women and men before conception has a profound implication for the growth, development and long-term health of their offspring.¹

New Zealand has one of the heaviest populations in the OECD, with a mean BMI of 27–31kg/m².There is evidence that women who are overweight or underweight have reduced fertility due to increased ovulatory infertility and increased complications of pregnancy.²

Women with BMIs >35kg/m² have a two-fold increase in the time required to conceive. A BMI >27kg/m² is associated with an increased risk of complications during pregnancy, such as gestational diabetes, pregnancy-associated hypertension, preterm birth, caesarean section and large for gestational age infants.

Low BMI (<18kg/m²) is associated with a four-fold increase in time to conception and with an increased risk of preterm birth and intrauterine growth restriction.

For men, a BMI >30kg/m² may affect testosterone levels and increase erectile dysfunction.

While the cut-off for publicly funded fertility treatment is a BMI of 32kg/m², it is a great idea to encourage your patients to make improvements to their lifestyle as it has a significant effect on overall health and fertility.

Take-home message: encourage your patients to achieve an optimal pre-pregnancy weight; if they have a high BMI, weight loss is a really good idea.

Weight loss of 5–10 per cent can significantly increase fertility by restoring menstrual cycle, which increases the chance of ovulation and conception.

It is important to approach the subject of weight sensitively, without bias or judgement. Involving the multidisciplinary team and identifying barriers is essential if solutions are needed to overcome them.

Physical activity is good for strength, stress and reducing cardiovascular disease risk factors, and it should be encouraged, particularly for patients with high BMIs. For general health, encourage being physically active for 30 minutes per day, most days of the week. For those trying to lose weight, the Ministry of Health recommends 300 minutes of moderate-intensity exercise per week, with two non-consecutive days of resistance/weight training.

It is also important to discuss the potential negative health consequences of too much exercise. There is some evidence that more than seven hours of strenuous aerobic exercise per week is associated with increased rates of anovulation.

Both caffeine and alcohol can have a negative effect on fertility. Advise women and men to reduce caffeine intake to 100–200mg per day – one to two cups of medium-strength coffee or tea appears to be suitable. Be mindful of cumulative caffeine sources, such as coffee, tea, cola, energy drinks, green tea/matcha, chocolate and cocoa. Encourage patients to slowly reduce caffeine intake and suggest introduction of de-caffeinated options, such as decaffeinated coffee and caffeine-free herbal teas.

Alcohol is known to cause defects in human embryos. For women, consuming more than seven standard drinks per week may be associated with irregular periods and a longer time to conceive. For men, more than 20 standard drinks per week reduces the number of pregnancies in their partner.

Antioxidants (found in fruits and vegetables) are nutrients that fight inflammation and neutralise free radicals which damage cellular health and DNA. The egg and sperm are highly sensitive to oxidative stress caused by free radicals, and antioxidants help protect them from possible corresponding damage.

When compared with fertile men, up to 25 per cent of infertile men have been found to have significant levels of free radicals in their semen.³ This may lead to cell death, sperm abnormality and motility loss, as well as damage to DNA, abnormal fertilisation, reduced implantation and poor embryonic development. Preventing cell damage by free radicals is important, and smoking, recreational drugs, alcohol, pollutants and infections are particularly damaging.

Take home message: encourage patients to stop smoking and taking recreational drugs, and to reduce exposure to environmental pollutants, such as BPA. Suggest eating a range of brightly coloured fruits and vegetables every day as most New Zealanders do not eat enough of these.

A Mediterranean-style diet has been shown to increase chances of conception. A Mediterranean-style diet includes fish, seafood, legumes and lots of fruits and vegetables, while reducing intake of processed foods, red meat, sugary food and takeaways. Overall, a Mediterranean-style diet is a basic healthy diet without too much processed food.

Research suggests that eating more plant sources of protein (legumes, kidney beans, tofu, edamame beans) and fewer animal sources may help improve ovulatory infertility – replacing 25g of animal protein per day with plant protein is associated with a 50 per cent lower risk.¹

Take home message: recommend more plant-based, minimally processed sources of protein, such as tofu, tempeh, beans, lentils, chickpeas, nuts and seeds. Suggest reducing meat by half or replacing at least one meat meal per week with a plant-based, protein-rich meal.

Evidence suggests women who consume diets high in monounsaturated fats (olive oil, avocados, salmon) have higher fertility rates.² For men, diets rich in anti-inflammatory omega-3 fatty acids improve sperm health, quality and motility, whereas high intake of saturated and trans fats adversely affect sperm quality.

Take home message: replace saturated fats (eg, butter, coconut oil) with monounsaturated fats (eg, olives, avocados, nuts and oily fish), while also being aware of portion sizes if weight is an issue. Reduce sources of saturated fat, such as animal fat, chicken skin, bacon and processed meats.

If eating a wide variety of foods, there shouldn’t be any need to take additional supplements before and during pregnancy, except folic acid and iodine. However, for those living south of Nelson Marlborough, vitamin D deficiency should be considered during late winter to early spring. Accumulating data suggest vitamin D may be important for fertility, with receptors located in the ovaries, placenta and endometrium as well as in the testicles and sperm.

Start making changes to diet and lifestyle at least three to four months before trying to conceive.

Choose a range of healthy foods from each of the four food groups (fruits and vegetables, grain foods, milk and milk products, and protein foods).

Increase antioxidants (fruits and vegetables) – the recommendations are now seven-plus a day for women (two serves of fruits and five of vegetables) and eight-plus a day for men.

Increase dietary fibre as it helps with hormonal control, bowel function and a healthy gut microbiome – encourage a variety of fruits, vegetables, legumes, wholegrains, nuts and seeds.

Choose lean animal and plant-based protein sources (eg, lean red meat, chicken, legumes, tofu, edamame beans), and reduce red meat to approximately one to two servings per week (if no problems with iron deficiency).

Avoid processed meat – foods high in sodium and nitrates are not good for fertility. Switch to smoked salmon or tuna, which provide good omega-3 fatty acids instead.

Include healthy fats (ideally olive oil or other plant-based liquid oils) and oily fish for omega-3 fatty acids (salmon, mussels, tuna, mackerel, sardines). One serving size of salmon is the size of a deck of cards (some salmon fillets at the supermarket are enough for two servings!). Tinned fish varieties are more economical. Vegetarian sources of omega-3 fatty acids include chia seeds, walnuts, flaxseeds/linseeds, edamame beans and hemp seeds.

Decrease saturated fat (animal fat and coconut fat), such as butter, meat fat, chicken skin, chips, pastries, biscuits and cream.

Decrease simple carbohydrates, such as “white flour type” products (eg, biscuits, muesli bars, processed breakfast cereals – choose rolled oats, plain Weetbix and plain Special K instead).

Choose moderate-fat dairy products, such as reduced-fat milk and yoghurts. Some studies (in ovulatory infertility) show high-fat dairy products may be better for fertility. However, these contain higher levels of saturated fat, so encourage reduced-fat dairy products for those trying to conceive. Dairy products are very good for calcium and protein, and most women in New Zealand do not have enough. Soy milk is the next best option in terms of nutritional completeness. If lactose intolerance is an issue, choose a zero-lactose milk or fortified soy milk. Most rice, almond and oat milks are a lot lower in protein, and some are not fortified with calcium – encourage patients to read nutritional labels.

Drink no more than two caffeinated drinks per day. Limit alcohol. Drink plenty of water.

As for artificial sweeteners and fertility treatment – watch this space. Artificially sweetened drinks are better than sugary drinks, but it’s best not to have too much. Encourage patients to drink plain water or plain reduced-fat milk. Also look for lifestyle drinks now available without sugar and artificial sweeteners.

Sarah Munn is a registered dietitian at Dietary Specialists private practice in Christchurch