Does red meat affect male fertility?

"Want to be a dad? Cut out sausages and eat chicken," the Daily Mail reports, prompted by the findings of a recent study into diet and fertility outcomes for couples undergoing fertility treatment.

This study analysed the diets of 141 men attending a fertility clinic with their partners for help getting pregnant. Sperm from men who reported a diet high in processed meat had less success fertilising eggs in the laboratory. But sperm from men who ate more chicken were more successful.

Crucially, however, none of these variations in diet affected the chance of the couples becoming pregnant after treatment, or having a baby. This means the study cannot prove that processed meat causes lower male fertility or that chicken boosts it. These associations could be valid, but there might also be other factors involved. And men who choose to avoid eating processed meat may also be healthy in other ways.

That said, eating a healthy, balanced diet low in processed meat certainly can't hurt in terms of boosting male fertility. Other methods include quitting smoking if you smoke, moderating your consumption of alcohol, and avoiding things that warm up your testicles, such as wearing tight underwear or having hot showers or baths, all of which can affect sperm production.

Where did the story come from?

The study was carried out by researchers from Harvard Medical School and Massachusetts General Hospital in the US, and Huazhong University of Science and Technology in China. It was funded by the US National Institutes for Health and the China Scholarship Council.

The study was published in the peer-reviewed medical journal Fertility and Sterility.

The Daily Mail's reporting of the study was of a high standard, signalling an appropriate note of caution: "Because the scientists looked only at statistics and did no health or lifestyle tests, they cannot draw any firm conclusions as to cause and effect. But they suspect the levels of fat and chemicals in processed meat may be significant."

The Mail provided the sound advice that, "Experts advised couples undergoing fertility treatment to eat a healthy diet." The article also included useful commentary from an independent expert, Allan Pacey, professor of Andrology at the University of Sheffield, who said: "I would be concerned that eating poultry is just a surrogate marker for some other aspect of a man's life which has not been measured here."

What kind of research was this?

This prospective cohort study looked at the effect of the male partner eating meat on a couple's success during fertility treatment.

Infertility is a common problem. Around one in seven couples may have difficulty conceiving, which is around 3.5 million people in the UK. It is usually advised you seek advice for potential infertility problems if you and your partner are unable to conceive after one year of trying.

Fertility treatments are also called assisted reproductive technology (ART). There are various options that may be considered, depending on the likely cause of the couple's fertility problems.

These include medications to help the woman release eggs, in vitro fertilisation (IVF), where the sperm and eggs are cultured in the laboratory and the embryo is then implanted, and intracytoplasmic sperm injection (ICSI), where a single sperm is injected directly into the egg.

Following a healthy lifestyle and maintaining a healthy weight through physical activity and a balanced diet, not smoking or using other substances, and moderating alcohol intake may also help boost the chances of conceiving.

The researchers say the possible impact of the man's diet on fertility has had a lot of attention recently, particularly the role of meat intake, which may influence sperm development. This was the focus of their new study.

This type of study can't prove cause and effect, as the couple were already having fertility problems at the time the male diet was assessed and many other factors could be involved. A randomised control trial, randomly allocating diets differing in meat intake, would be required for this.

However, there would likely be several ethical issues of randomising a man attending a fertility clinic to high or low meat intakes to see if this had an effect. For example, there could be a possible time delay for any effects and the known adverse health effects of a high-meat diet, such as an increased risk of bowel cancer.

What did the research involve?

The research gathered dietary information from 141 men whose partners were having fertility treatment to help them conceive between 2007 and 2014. All of the couples in this study were receiving IVF or ICSI. The amount and type of meat intake by the male partner was estimated from dietary questionnaires.

They wanted to see if the amount and type of meat affected fertility success, which was defined in a number of ways:

fertilisation rate – the proportion of female eggs successfully fertilised by male sperm in the laboratory
implantation rate – the percentage of embryos successfully implanted into the women's womb
pregnancy rate – the percentage of fertility cycles (attempts) leading to a pregnancy
live birth rate – the percentage of fertility cycles leading to a live birth

The analysis took account of factors (confounders) known to affect fertility in addition to meat intake, including:

total energy intake
age
body mass index
alcohol
caffeine
prudent dietary pattern – a diet high in fruit, vegetables, wholegrain foods, poultry and fish
western dietary pattern – a diet high in red and processed meat, sugary desserts, high-fat foods and refined grains

Taking account of these factors helps isolate the individual effect of eating meat against everything else.

What were the basic results?

Processed meat was linked to lower fertilisation rates, whereas eating more chicken was linked to higher fertilisation rates.

Men's total meat intake, including their intake of specific types of meat, was not associated with implantation, pregnancy or live birth rates.

There was a 13% higher fertilisation rate in men in the highest quarter of poultry intake compared with those in the lowest quarter (78% versus 65%).

Processed meat intake was inversely related to fertilisation rate in couples having conventional IVF – that is, as processed meat intake went up, the fertilisation rate went down.

The fertilisation rates for men in increasing quarters of processed meat intake were 82% (lowest quarter of processed meat intake), 67%, 70% and 54% (highest processed meat intake) in conventional IVF cycles.

Processed meat intake was not associated with fertilisation rate in couples receiving ICSI.

How did the researchers interpret the results?

The authors concluded that, "Our study expands the growing literature regarding the relationship between diet and markers of male fertility.

"However, owing to the scarcity of data on how men's diets in general and meat intake in particular influence infertility treatment outcomes, further research is needed to clarify these relations to allow the formulation of clinically relevant recommendations in the future."

Conclusion

This study of a cohort of men attending a fertility clinic for help to conceive found fertilisation rates in the laboratory during IVF were less successful if men reported a diet high in processed meat, and more successful if they ate more chicken.

Importantly, the effect of overall meat intake was not related to fertility success, which is the chance of becoming pregnant after the treatment cycles, or having a live birth.

It was also not clear whether the variation in fertility rate influenced how many cycles of IVF were needed, or how long the couple needed medical assistance, before they became pregnant or had a child. If more IVF cycles were needed, this would be more expensive, especially if people are paying for private fertility treatment.

So what does this mixed bag of results tell us? It does not tell us processed meat causes lower fertility or chicken boosts it. That could be true, but there could be lots of reasons why the individual couples at the fertility clinic had difficulty conceiving – not all related to male fertility.

Also, the amount of processed meat men eat could be a marker of how generally healthy their diet is, or how healthy they are in general, both of which may influence sperm development and fertility. The researchers did attempt to account for this in their analysis, but this might not completely eliminate the effects. Other relevant factors, such as smoking, have not been taken into account.

The researchers say they previously found a link between meat intake and changes in sperm shape in sub-fertile men attending a fertility clinic. This gives a potential biological mechanism explaining how meat might be linked to fertility, but again it might not necessarily be because of meat – it could be the wider diet, or something else entirely.

The results are relevant to couples receiving fertility treatment. However, they are not directly relevant for people conceiving without medical assistance. In fact, a useful exercise would be to compare the diets of men from couples needing fertility assistance with those who got pregnant naturally.

Though the theory of meat intake influencing sperm development is plausible, for all we know these men may be eating much less meat than those who have had no trouble conceiving naturally.

The study is consistent with current advice to follow a healthy, balanced diet. Though this study does not prove a high intake of processed meat reduces male fertility, it has been linked to other adverse health risks – notably bowel cancer.