Drinking whole fat milk and eating ice cream appears to be better for women trying to become pregnant than a diet consisting of low-fat dairy products such as skimmed milk and yoghurt, according to new research published in Europe's leading reproductive medicine journal, Human Reproduction, today (28 February). 
Researchers in the United States have found a link between a low-fat dairy diet and increased risk of infertility due to lack of ovulation (anovulatory infertility). Their study showed that if women ate two or more servings of low-fat dairy foods a day, they increased their risk of ovulation-related infertility by more than four fifths (85%) compared to women who ate less than one serving of low-fat dairy food a week. On the other hand, if women ate at least one serving of high-fat dairy food a day, they reduced their risk of anovulatory infertility by more than a quarter (27%) compared to women who consumed one or fewer high-fat dairy serving a week.
Lead author of the study, Dr Jorge Chavarro, who is a research fellow in the Department of Nutrition at Harvard School of Public Health, Boston, Massachusetts, USA, said that, given the scarcity of information in this area, it was important that more research should be carried out into the association between low-fat dairy foods and anovulatory infertility in order to confirm or refute the findings.
"Clarifying the role of dairy foods intake on fertility is particularly important since the current Dietary Guidelines for Americans recommend that adults consume three or more daily servings of low-fat milk or equivalent dairy products: a strategy that may well be deleterious for women planning to become pregnant as it would give them an 85% higher risk of anovulatory infertility according to our findings."
In the meantime, he said that his advice to women wanting to conceive would be to change their diet. "They should consider changing low-fat dairy foods for high-fat dairy foods; for instance, by swapping skimmed milk for whole milk and eating ice cream, not low fat yoghurt." However, he said that it was important that women did this within the constraints of maintaining their normal calorie intake and limiting their overall consumption of saturated fats in order to maintain general good health. "Once they have become pregnant, then they should probably switch back to low-fat dairy foods as it is easier to limit intake of saturated fat by consuming low-fat dairy foods," he said.
In their prospective study, Dr Chavarro and his colleagues identified 18,555 women, aged between 24 and 42, without a history of infertility, who had tried to become pregnant or had became pregnant between 1991 and 1999. The women were part of a much larger study of 116,000 women in The Nurses' Health Study II.
Every two years the women completed a questionnaire that asked if they had tried to become pregnant for more than a year without success, and what the cause was if they had been unable to conceive. The women also supplied information on how often, on average, they had consumed certain foods and drinks during the previous year. During the eight years, 438 healthy women reported infertility due to an ovulatory disorder.
After adjusting for various factors such as age, parity, body mass index, total calorie intake, physical activity, smoking, drinking and contraceptive use, the researchers found an 85% increased risk of anovulatory infertility in women eating two or more servings of low-fat dairy food a day compared to women eating one or fewer servings a week, and a 27% decreased risk of infertility for women eating high-fat dairy food one or more times a day compared to women eating a serving one or fewer times a week.
Dr Chavarro said: "Intake of total dairy foods was not associated with the risk of anovulatory infertility, but when the low-fat and high-fat foods were considered separately, we found a positive association between low-fat dairy food intake above five servings a week and risk of anovulatory infertility, and an inverse association between high-fat dairy food intake and risk of developing this condition."
Further analysis of the findings in which specific foods were investigated, showed that an extra serving per day of a low-fat dairy food such as yoghurt, appeared to increase the risk of anovulatory infertility by 11%, if the total daily intake of calories was unchanged. In contrast, an extra daily serving of a high-fat dairy food such as whole fat milk was associated with a 22% lower risk (with an unchanged calorie intake). The study showed that the more ice cream the women ate, the lower was their risk, so that a woman eating ice cream two or more times a week had a 38% lower risk compared to a woman who consumed ice cream less than once a week.
The researchers believe that the presence of a fat-soluble substance, which improves ovarian function, might explain the lower risk of infertility from high-fat dairy foods. "The intake of dairy fat, or a fat-soluble substance present in dairy foods, may partly explain the inverse association between high-fat dairy foods and anovulatory infertility," said Dr Chavarro.
Previous studies had suggested that lactose (a sugar found in milk) might be associated with anovulatory infertility, but Dr Chavarro's study found neither a positive nor negative association for this, and nor was there any association between intake of calcium, phosphorus or vitamin D and anovulatory infertility.
 A prospective study of dairy foods intake and anovulatory fertility. Human Reproduction. doi:10.1093/humrep/dem019.