Dr. Mònica Bulló, Associate Professor of Human Nutrition Unit, Faculty of Medicine and Health Sciences, Rovira i Virgili University, Spain.
First of all, could you explain what is the background behind the study?
Infertility is estimated to affect about 15% of all reproductive-age couples and 40-50% of cases are due to the male. Potential causes of infertility are associated with lifestyle, which includes dietary habits. Moreover, sperm quality may be modulated by inflammatory and oxidative processes, among others, thus compromising fertility. Since nuts modulate some of these molecular processes, we thought they should play a role in sperm quality.
Which was the starting point of this project?
In many fertility clinics antioxidant or other dietary supplements are recommended in order to improve fertility. However, the scientific evidence for these recommendations is very low. Some observational studies and randomized controlled trials have found that the adherence to a healthy diet, rich in omega-3, some antioxidants such as vitamin C and E, selenium and zinc, carnitines and folate, may improve semen quality and fecundability in men. Given that nuts are particularly rich in some of these nutrients, their consumption should beneficially affect semen quality.
What was the aim of the study?
The aim of the study was to demonstrate a beneficial role of regular consumption of nuts on classic and novel sperm quality parameters, which could be linked to an improvement in male fertility. The classic parameters include semen volume, total sperm count and concentration, vitality, motility and morphology, and are commonly used for clinical diagnoses. However, our study wanted to go further and so we looked in detail at potentially new markers at molecular levels including sperm DNA fragmentation, reactive oxygen species, micro RNAs, DNA methylation and chromosomal anomalies. These parameters are beyond those commonly assessed but we suspected that they would be closely related.
119 young men participated in the research. Can you give us a description of the study? This was a randomized controlled study conducted on 119 healthy males who follow a western-style diet, which is vastly different from a Mediterranean one. Participants were assigned to either a group that followed their usual diet supplemented with 60 g/day of mixed nuts (almonds, hazelnuts and walnuts) or their usual nut-free diet for 14 weeks. And now you may ask, why 14 weeks? Well, because that’s the sperm cycle.
Can you explain its main conclusions? I can proudly say that our hypotheses were true. The main results of the study demonstrate that regular nut consumption, in an otherwise imbalanced diet, improved sperm quality parameters such as total sperm count, vitality, motility and morphology and that the findings could be partially explained by a reduction in sperm DNA fragmentation. However, whether our findings can be translated into increased male fertility requires further studies. At this moment in time we can only assume that regular nut consumption improves the quality of sperm. In the same way, we saw other tendencies and statistics in other fields but these also require further studies.
So, could nut consumption help improve male fertility? We demonstrated an improvement in several parameters that could contribute to male fertility. However, we did not analyze fertility by itself. The classical parameters which we found to be beneficially modulated by nut consumption have been linked to increased male fecundability and fertility, but not the novel ones. The study provides evidence for the first time that nuts can have other medical functionalities beyond everything that has already been proved in biomedicine, such as improvements in the field of cardiovascular disease. We have before us an open window. It’s a matter of continuing to investigate
What specifically do nuts contain to potentially increase the number and quality of sperm? Nuts are remarkable for their bioactive compounds. They are high in several components, such as proteins, fiber, fat, MUFA, PUFA, magnesium, vitamin E, omega-3, ALA, omega-6 and are high in substances directly related to anti-inflammatory and anti-oxidant compounds. So, if the hypothesis was that inflammation and oxidation negatively affect fertility, why shouldn’t nuts be beneficial?
What level of daily nut consumption would you recommend to potentially improve sperm count? In our study we used 60 g/day and we did not conduct any dose-response analysis, so we do not have information regarding whether lower doses could bring the same benefits.
Infertility is a major issue nowadays. Are you planning to continue your investigations further in this area? There are still some results derived from the study that deserve further analysis and we will also analyze DNA methylation in more depth in order to identify new potential markers of sperm quality.
What’s the next step? What are the implications of the research? Could this study open the door to new investigations? One of the next steps being studied is the role of DNA methylation in improvements in classic sperm parameters (seminogram). To demonstrate that a food group such as nuts can modulate sperm quality parameters is of great interest in developing public health strategies in developed countries where infertility seems to have fallen drastically. We believe our findings open new avenues for research into how they can be translated into an increase in the chances of fertility and whether nut consumption also has a positive effect on female fertility.
So, would you recommend eating nuts to increase fertility? I would say: Why not? Nuts are rich in beneficial compounds. In this study, we are not saying that they can raise male fertility to 100%, because there are so many other factors to be taken into account, but we have found solid evidence that they improve sperm quality patterns.