Both studies were presented in Istanbul at the 28th annual meeting of the European Society for Human Reproduction and Embryology (ESHRE).
However, other experts consulted by WebMD warn that both studies are small and it's too soon to recommend drastic dietary changes based on the findings.
"In a small study, all sorts of spurious results can come out," says Richard Paulson, MD, professor of reproductive medicine and head of the fertility program at the University of Southern California in Los Angeles.
About 1 in 6 couples worldwide have some type of infertility problem during their reproductive years, according to ESHRE. Since 1978, about 5 million babies worldwide have been born with the help of fertility treatments.
Diet & IVF Success: Coffee Study
For the coffee study, Kesmodel evaluated nearly 4,000 cycles in women undergoing infertility treatments at a Denmark clinic.
At the start of the treatment and before each treatment cycle, the women reported how much coffee they drank per day. Kesmodel also took into account age, smoking, alcohol habits, weight, and other factors that may affect the success of fertility treatments.
Those who drank more than five cups of coffee a day cut their chances of achieving pregnancy.
"They have only half the chance of achieving pregnancy compared to women who do not drink coffee at all," Kesmodel tells WebMD.
The finding needs to be repeated in other studies, Kesmodel warns. But if the current study turns out to be valid, the effect of heavy coffee drinking on IVF success would be about the same as the known risk of smoking during IVF.
"I am not saying people [undergoing IVF] should not drink coffee at all," Kesmodel tells WebMD. "One or two cups a day would likely be okay."
He can't explain the link, and points out that he found evidence only of an association between heavy coffee drinking and odds of IVF success, not proof that coffee causes IVF failure.
Diet & IVF Success: Fats
In previous research, Chavarro and his team found links between trans fats and saturated fats and fertility problems.
In the new study, he evaluated 147 women having IVF at the Massachusetts General Hospital Fertility Center.
He grouped the women into categories depending on how much of three different kinds of fat they ate.
He also took into account their body mass index, smoking habits, and infertility diagnosis, all of which could affect their treatment.
- Women who ate the most saturated fats (found mostly in animal food sources) had fewer mature oocytes -- cells that form eggs.
- Women who ate the most polyunsaturated fats (found in plant-based foods and oils) had more poor-quality embryos than those who ate the least.
- Women who ate the most polyunsaturated fats also had a 12% higher proportion of cells in the embryo that were dividing more slowly than expected.
- Higher levels of monounsaturated fats (found in oils and many foods and found to improve cholesterol) increased the chances of a live birth after embryo transfer. Those who ate the most were about 3.5 times more likely to have a live birth than those who ate the least.
The amount of fats eaten varied. For instance, those in the lowest monounsaturated group ate about 9% of calories from this fat. Those in the highest group, about 25%.
Chavarro can't explain the links. "At this point it is not entirely clear what the underlying mechanisms explaining these associations might be," he tells WebMD.
Diet & IVF Success: Perspectives
No dietary advice changes should be based on the new research, experts who reviewed the findings agree.
"The coffee finding is not a shock," says Harry Lieman, MD, interim division director of reproductive endocrinology and infertility at Montefiore Medical Center/Albert Einstein College of Medicine in Bronx, N.Y.
In studies of women trying to conceive without IVF, he says, increased caffeine intake has been linked with an increased length of time to get pregnant.
He already tells his IVF patients not to drink more than two cups of coffee daily. "Now I have IVF evidence," he says.
The finding that women drinking five or more cups of coffee a day fared worse in IVF treatment may simply reflect other extreme habits, Paulson says.
"Anyone who drinks five cups of coffee a day probably has other habits that are not ideal," he suggests. "We cannot conclude from this study that coffee in and of itself interferes with having a good pregnancy outcome following IVF."
Paulson tells his IVF patients they can indulge in one cup of coffee a day, even if it is coffee-house coffee -- typically double the serving size at home.
"Drinking coffee in excess, based on this study, does seem to have a detrimental effect," says Peter Klatsky, MD, assistant professor of reproductive medicine at Montefiore Medical Center/Albert Einstein College of Medicine.
However, the findings may apply to a small percentage of patients, he says. "Most patients are not drinking five or more cups," he says.
The research on fat is too new to trigger diet advice changes, the experts agree.
Until more research is in, the experts who reviewed the findings suggest women undergoing IVF stick with the same guidelines as others. The Dietary Guidelines suggest keeping saturated fat intake low and total fat intake moderate.
This research was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.
SOURCES: Ulrik Kesmodel, MD, PhD, consultant gynecologist, Fertility Clinic of Aarhus University Hospital, Aarhus, Denmark.Jorge Chavarro, MD, ScD, assistant professor of nutrition and epidemiology, Harvard School of Public Health; assistant professor of medicine, Harvard Medical School, Boston.28th Annual Meeting, European Society of Human Reproduction and Embryology, Istanbul, July 1-4, 2012.Richard Paulson, MD, professor and vice chair, obstetrics and gynecology; chief, division of reproductive endocrinology and infertility, Keck School of Medicine, University of Southern California, Los Angeles.Harry Lieman, MD, interim division director of reproductive endocrinology and infertility, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, N.Y.Peter Klatsky, MD, MPH, assistant professor of reproductive medicine, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, N.Y.
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