Adhering to a Mediterranean diet - rich in fruits, vegetables, fish, whole grains and healthy fats - may significantly improve sperm quality in men, a new study claims.

Infertility is a global public health issue and affects 15 per cent of all couples of reproductive age. Male factors, including decreased sperm quality, are responsible for about 25 per cent of these cases, researchers said.

Researchers at the Universitat Rovira I Virgili and the Pere i Virgili Health Research Institute in Spain conducted the first systematic review of all observational studies on sperm quality and male fecundability (reproductive rate) and their relationship with diet, food and nutrient consumption.

The results indicate that low sperm quality parameters are inversely associated with healthy diets rich in certain nutrients such as omega-3 fatty acids, certain antioxidants (vitamin E, vitamin C, beta-carotene, selenium, zinc, cryptoxanthin and lycopene), other vitamins (vitamin D and folate) and low saturated fatty acids and trans-fatty acids.

Fish, shellfish, seafood, poultry, cereals, vegetables and fruits, low-fat dairy and skimmed milk were positively associated with several sperm quality parameters.

In contrast, diets rich in processed meat, soy foods, potatoes, full-fat dairy and total dairy products, cheese, coffee, alcohol, sugar-sweetened beverages and sweets have been associated with lower-quality sperm in some studies.

A high intake of alcohol, caffeine, red meat and processed meat by males has a negative influence on the chance of pregnancy or fertilisation rates of their partners.

According to the researchers, the review has provided a comprehensive overview of existing high-quality research into the effect of diet and the consumption of different foods and nutrients on fecundability and male fertility so that safer and more effective dietary recommendations can be made in the future.

These results highlight the fact that adherence to a healthy diet, eg the Mediterranean diet, by men could significantly improve their sperm quality and the fecundity of their partners.

In order to improve sperm quality and fertility changes, many fertility clinics recommend simple lifestyle changes such as increased physical activity, cognitive behavioural therapy or yoga to reduce stress, give advice on how to reduce alcohol and caffeine intake and provide lists of dietary recommendations.

However, there is a lack of a proven scientific evidence regarding the role of diet in determining sperm parameters.