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Research warning against too much fat and animal protein is part of a growing recognition of the role of lifestyle factors in infertility -- for women and men

Paleo buzzkill

All that meat could be hurting your fertility

By Sarah Elizabeth Richards on November 8, 2015

If you’re trying to get pregnant, you suddenly become aware of how every bite you put into your mouth might affect your fertility. The vigilance is justified: Research over the last decade has made a convincing case that a high-protein, low-carb diet is best for conceiving.

First came news that refined carbohydrates and sugar could wreak havoc on your blood sugar and insulin levels and disrupt your hormones, followed by a study suggesting that patients who ate more protein and fewer carbohydrates had a fourfold greater chance of IVF success than bread and pasta lovers. Yet a handful of new studies now shows that swapping cake pops for bacon isn’t a good strategy, either. (That’s in addition to last week’s World Health Organization bombshell that processed meats cause colorectal cancer.)

The research – separately warning against too much fat and animal protein – is part of a growing recognition of the role of lifestyle factors that some scientists believe might be responsible for the one-third of infertility cases that doctors can’t attribute to old eggs, weak sperm or blocked Fallopian tubes. The recent research is also important because it shows the effect of diet on fertility for both women and men — independent of one’s weight. (Ob-gyns are on message to warn women that obesity is pregnancy enemy number one.)

Azucena Sanchez arranges processed sausages for curing at the small family-run 'Sierra de las Villuercas' traditional sausage processing plant on October 29, 2015 in the village of Deleitosa, in Extramadura province, Spain. (Photo by Denis Doyle/Getty Images)
A recent World Health Organization announcement linked cancer to red meats and particularly processed meats like sausages. (Denis Doyle/Getty Images)

In the first study, researchers from the University of Colorado Denver found that female mice fed a high-fat diet consisting of 60 percent lard for 10 weeks had significantly compromised fertility, whether they were fat or thin. The researchers cut open the mice’s ovaries and found that in addition to increased inflammation the lard eaters had nearly half as many primordial follicles as the control group. (These are the undeveloped eggs that females are born with and continually die off until menopause.) “I had thought that as long as someone was lean, a high-fat diet wouldn’t affect her reproductive function, so this was a surprise,” explained lead author Malgorzata Skaznik-Wikiel, MD, who presented the study at the annual meeting of the American Society for Reproductive Medicine (ASRM) last month. Other mice that were fed the lard diet ended up giving birth to fewer pups per litter.

Obviously, the study has limitations, considering that few of us eat a diet that high in fat, never mind lard. But it’s definitely an indictment against the saturated fat found in red meats, butter and cheese. (The American Heart Association recommends we limit our intake of that kind of fat to less than 5 percent of total calories.) Next, the researchers will study whether the effect is true for healthier fats, such as olive, sunflower and fish oils.

In another study, a Harvard team tracked whether men’s consumption of trans fats hurt their sperm quality. The researchers analyzed the dietary histories of 141 men undergoing IVF treatment with their partners and found that those who had consumed more trans fats had poorer fertilization rates. “What was shocking was that the amount of trans fats wasn’t even that much,” explained lead author Mariel Arvizu, a doctoral candidate in nutrition at the Harvard School of Public Health. “We considered a portion of French fries to be a large amount.”

A man eats "curry wurst and pommes" a German sausage with French Fries and mayonnaise from a street vendor in Berlin on 25 August , 2011. The dish is second only to the Doner kebab as the German's favorite fast food. AFP PHOTO / ODD ANDERSEN (Photo credit should read ODD ANDERSEN/AFP/Getty Images)
Harvard researchers found men undergoing IVF treatment with their partners who had consumed more trans fats had poorer fertilization rates. (ODD ANDERSEN/AFP/Getty Images)

Although the U.S. Food and Drug Administration announced this summer it will phase out trans fat — also known as partially hydrogenated oils — over the next three years, it can still be found in many margarines, processed cookies and crackers and coffee creamers. The research is significant because it’s one of the first clinical human studies to evaluate the effect of fat on sperm. “This shows that men have an active role in the reproduction process from the beginning,” said Arvizu.

While it’s important to embrace good nutrition if you’re trying to prepare your body to grow a human being, fertility doctors caution against putting too much stock in the advice du jour. “The problem is that studies often fall on both sides of the fence. For example, some say dairy is helpful to fertility, and some say it’s not,” said Owen Davis, MD, reproductive endocrinologist at Weill Cornell Medical College and ASRM president. Case in point: The rate of infertility is constant around the word — whether you’re eating vegetarian meals in India or enjoying asado in Argentina.

Besides maintaining a healthy weight and consuming enough folic acid and vitamin D, women are advised to restrict caffeine and alcohol and aim for a diet rich in lean meats, whole grains, fruit and vegetables. (New recommendations include future dads, too.) “Beyond that, we don’t have enough strong evidence to say it’s bad to eat a lot of protein,” he said.

However, as in most articles on diet and health, the best recommendations come back to the darling of nutritional studies: the Mediterranean Diet. A 2010 Dutch study of 161 couples undergoing fertility treatment found that those who ate a diet rich in vegetable oils, fruit, fish and whole grains had a 40 percent better chance of conceiving than those who indulged in mayonnaise, snacks and meat products. Those findings inspired British researcher Alexandra Kermack at the University of Southampton to test the anti-inflammatory effects of omega-3 in what would be found in a serving of salmon on women starting six weeks before undergoing IVF.

“We don’t know the mechanisms how any of these dietary interventions work,” said Kermack, whose previous research on amino acids showed that diet affects the nutritional composition of the womb and might determine whether embryos implant and thrive. “But it’s essential we figure this out because we need to make sure women have the right advice.”

Sarah Elizabeth Richards is a health and science journalist and author of Motherhood, Rescheduled: The New Frontier of Egg Freezing and the Women Who Tried It.


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