The inclusion of nuts in a regular diet significantly improves the quality and function of human sperm, according to results of a randomised trial which measured conventional semen parameters and molecular changes over a 14-week study period. The findings, say the investigators, "support a beneficial role for chronic nut consumption in sperm quality" and reflect a research need for further male-specific dietary recommendations.

The results of the study are presented today by Dr Albert Salas-Huetos from the Human Nutrition Unit of the Universitat Rovira i Virgil in Reus, Spain.(1)

The study was performed, he said, against a background of general decline in quantity and quality of human sperm, attributed in industrialised countries to "pollution, smoking, and trends toward a western-style diet." (2) In this study subjects randomised to the nut group had significant improvements in their sperm count, vitality, motility and morphology (shape); these were consistent with improvements found in other recent studies with diets rich in omega-3, antioxidants (eg, vitamin C and E, selenium and zinc), and folate. Nuts are dense foods containing many of these nutrients and other phytochemicals.

The study was a 14-week randomised clinical trial in which 119 healthy young men aged 18-35 were allocated to either their usual western-style diet supplemented with 60 grams/day of mixed almonds, hazelnuts and walnuts, or their usual western-style diet without nuts. In its analysis the study recorded not just sperm parameters (according to WHO benchmarks) but also changes in several molecular factors, including sperm DNA fragmentation.(3) Sperm and blood samples were analysed at baseline and after 14 weeks of intervention.

Results firstly found significantly higher levels of sperm count, vitality, motility and morphology in the men randomised to the 60 g/day nut diet than in those following their usual diets free of nuts. Improvements in the former group were by around 16% in sperm count, 4% in sperm vitality, 6% in sperm motility, and 1% in morphology. These four parameters, explained Salas-Huetos, are all associated with male fertility. Moreover, the subjects in the nut group also showed a significant reduction in their levels of sperm DNA fragmentation, a parameter closely associated with male infertility. Indeed, it was this change in the level of DNA fragmentation in the sperm cells by which the investigators explained, at least in part, the improvement in sperm count, motility and morphology.

Although these are statistically significant results from a randomised trail with a high level of scientific evidence, Salas-Huetos emphasised that subjects in the study were all healthy and apparently fertile men following a western-style diet. He thus warned that results cannot be extrapolated to the general population.

So should men hoping to conceive a baby -- either naturally or with IVF -- add nuts to their everyday diet? "We can't yet say that," said Salas-Huetos, "based solely on the results of this study. But evidence is accumulating in the literature that healthy lifestyle changes such as following a healthy dietary pattern might help conception -- and of course, nuts are a key component of a Mediterranean healthy diet."

1. This was a collaborative study led by Dr Mònica Bulló from the Rovira i Virgili University and Drs Joan Blanco and Ester Anton from the Autonomous University of Barcelona. The study was funded by the International Nut and Dried Food Council.

2. There remains some controversy over a decline in sperm counts in developed countries, mainly because of how the measurements were taken. However, a huge meta-analysis last year reported "a significant decline in sperm counts between 1973 and 2011." The analysis, which included more than 40,000 men whose semen samples were screened in 244 studies, found the results "driven by a 50-60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand." The decline in sperm concentration was put at -1.4% per year and in total sperm count at -1.6% per year. (See Levine H, Jørgensen N, Martino-Andrade A, et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Hum Reprod Update 2017; 23: 646-659.)

3. The World Health Organization lists four semen quality parameters in its latest manual of 2010: concentration (ie, count, which should be a minimum of 15 million sperm cells per ml semen); progressive motility (32% minimum); vitality (58%); and morphology (4%). These are the main parameters measured to evaluate semen quality within a normal range. At the molecular level it has also been proposed that the genetic integrity of each sperm cell is essential for successful fertilisation; if DNA strands in the cell become damaged or fragmented, they will be unable or less likely to fertilise an egg and maintain embryonic development. It is believed that this DNA fragmentation is caused by oxidative stress as a result of environmental and lifestyle factors. Sperm DNA fragmentation can be tested by a range of assays.