Good for sperm
In the new study, researchers at UCLA recruited 117 healthy young men and gave walnuts to half of them for 12 weeks. At the end of that period, the walnut-eaters's sperm had better motility, while their sperm were also less likely to be malformed. A caveat: the study was partially funded by the California Walnut Commission, who also provided the walnuts.
A 2008 study found that men with diets high in folate — found in leafy greens and some fruits — had fewer sperm with the wrong number of chromosomes. Extra or missing chromosomes can cause a variety of congenital conditions, like Down's syndrome. Having lots of sperm with chromosome problems can also contribute to infertility.
The Peruvian maca plant
The plant, which can be taken in supplement form, appeared to increase sperm count and motility in one study. However, the study only looked at nine men, and most other research into maca's usefulness appears to have been done on rats.
Bad for sperm
A 2007 study found that men who used cell phones four hours or more per day had lower sperm quality than less phone-obsessed men. Followup research suggested that cell phone placement might matter — placing a cell phone right next to a cup of semen for an hour appeared to damage the sperm. So keeping a cell phone in a pants pocket may be ill-advised. No word on the potential fertility impact of dick pics.
In 2008, researchers found that stressed men had lower numbers of healthy sperm than men in a control group. One upside: therapy appeared to help bring sperm health back to normal.
Unfortunately, one study showed selective serotonin reuptake inhibitors (drugs like Prozac and Zoloft) lowered men's sperm count and damaged their sperm's DNA. So for men worried about the effects of stress on their fertility, SSRIs may not be the answer.
A study earlier this year found that men whose diets were high in saturated fat had lower sperm count and concentration than guys who ate lower-fat foods. Omega-3 fats like those found in fish, though, improved sperm quality.
Smoking marijuana can lower sperm count, according to a 2003 study. It can also make sperm move too quickly, unlike pot-smokers themselves. However, another study published this year found no effect of recreational drug use on sperm count.
The same study that found drugs are fine for sperm also found that men with low sperm quality were more likely than others to wear tight underwear as opposed to loose boxers. Study author Allan Pacey said men who wanted to boost their fertility should consider switching to looser options.