Last week a story in the British press on possible hazards of meat eating drew enough attention that the National Health Service (NHS) felt compelled to let people know that the study was not as significant as the promotion made it out to be.
"The study was small and has limitations because of its design. This research should be regarded as preliminary evidence, and larger studies will be needed to explore whether diet does affect semen quality," the NHS said.
The NHS noted that the study found men who consumed more protein had sperm abnormalities, the study had not even looked at where the protein had come from.
"One of the challenges in designing studies that look at nutrient in male fertility is designing a well-monitored study of what men are really eating," said Williams.
He noted that the effects of foods and environments can vary between individuals.
"Those are factors that are very difficult to control when you're doing a research study about male infertility."
Undetermined -- But Worth Watching
"Unfortunately, there aren't any good well-controlled studies that investigate the direct effect emotional stress has on male factor fertility," said Williams.
He noted that the concern behind emotional stress is not on sperm production but on the effect infertility might have on the couple.
Because infertility can be so stressful, he said, he often refers couples to a counselor to help them through the process emotionally.
"Any strategies or coping mechanisms that help with stress management can certainly be beneficial as they go through the fertility process," said Williams.
"But whether or not the stress management directly improves the testicular function and production of sperm is unknown at this point."
Moalem notes that there might be some physiological reasons why emotional stress would cause fertility problems.
When the fight or flight response is triggered, he said, "you spend more energy…to get you out of a bad situation than to maintain the body.
"Our body's not geared toward reproduction as much."
For that reason, he said, when women are under a lot of stress, it can actually bring on an early period, perhaps the body's way of saying "It may not be the best time to have kids."
Moalem noted, however, that "I haven't seen any studies that do a good job for [the effect of stress on fertility]. It's very hard to study because it's so individual."
Obviously aging itself can't be avoided, but ignoring the biological clock when deciding when to have kids can be a problem for men as well as women.
"Certainly the impact of age and fertility is better established and more pronounced in women than in men, but there is growing evidence that with time the quality of men's sperm declines," said Williams. "There can be impaired sperm quality with advanced paternal age.
"There are some studies that demonstrate that when combined with advanced maternal age, that advanced paternal age can put offspring at risk for certain conditions like Down's syndrome, autism and schizophrenia, but there's active research going on in this field of advanced paternal age to better answer these questions."
Morgentaler, however, notes that advanced paternal age is still less of a concern than advanced maternal age.
"There is an age-related decline in sperm numbers," he said, but "Male fertility is very different from female fertility.