Ice Cream and Whole-Fat Milk Smooth the Way to Conception

BOSTON, Feb. 28 -- Eating rich ice cream and drinking whole-fat milk, and using heavy cream for coffee, may help reward women shooting for pregnancy, researchers here reported.

On the other hand, if pregnancy is not the goal, low-fat dairy foods, such as skimmed milk and low-fat yogurt, may the better bill of fare.

In a turn-about from the standard health prescription, researchers found that women who ate two or more portions of low-fat dairy foods a day increased their risk of ovulation-related infertility by 85%, compared with women who ate less than one portion a week, reported Jorge Chavarro, M.D., Sc.D., of the Harvard School of Public Health here, and colleagues, in the Feb. 28 issue of Human Reproduction.

If women ate at least one portion of high-fat dairy food a day, their risk of anovulatory infertility was 27% lower compared with women who had one high-fat dairy serving a week, or even less.

To determine whether the intake of dairy foods was associated with anovulatory infertility and whether this association differed according to fat content, the researchers prospectively followed 18,555 married premenopausal women without a history of infertility.

The women, participants in the Nurses' Health Study II, attempted a pregnancy or became pregnant over eight years (1991 to 1999). Diet was assessed twice during the study using food-frequency questionnaires.

During follow-up, 438 women reported infertility because of an ovulatory disorder. Intake of total dairy foods was not associated with the risk of anovulatory infertility, but the association with infertility appeared when low-fat and high-fat foods were considered separately.

After adjusting for various factors, such as age, parity, body mass index, total calorie intake, physical activity, smoking, drinking, and contraceptive use, the results were as follows: The multivariate-adjusted relative risk of anovulatory infertility comparing women consuming two or more low-fat servings a day with women consuming one or fewer servings a week was 1.85 (95% CI 1.24-2.77; P trend=0.002) for low-fat dairy foods.

The relative risk comparing women consuming one or more servings per day of high-fat dairy foods to those consuming one or fewer servings a week was 0.73 (CI 0.52-1.01; P, trend = 0.01).

Overall, there was an inverse association between dairy-fat intake and anovulatory infertility (P, trend = 0.05), the researchers reported.

Further analysis in which specific foods were studied, showed that an extra serving a day of a low-fat-dairy food, such as yogurt, appeared to increase the risk of infertility by 11%, if the total calorie intake 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.

Low-fat dairy foods included yogurt or sherbet, skim or low-fat milk, and low-fat cottage cheese. High-fat foods included whole milk, ice cream, whipped or heavy cream, sour cream, cream cheese, and other cheeses.

The study also found that the more ice cream the women ate, the lower their risk, so that a woman eating ice cream two or more times a week had a 38% lower risk compared with a woman who ate ice cream less often than once a week.

Intakes of lactose, calcium, phosphorus, and vitamin D were unrelated to anovulatory infertility, the researchers reported. It had been thought that dairy fat and lactose might impair fertility by affecting ovulatory function, they said. However, few studies have been conducted in humans, and the results are inconsistent.

In the current study, there was neither a positive nor a negative association for lactose and fertility within the usual range of intake levels in humans, they said.

In discussing the association between the low-fat diet and infertility, the researchers discussed the possibility that women with or with suspected polycystic ovary syndrome who changed their diet to include more low-fat foods would be likely to have anovulatory infertility. This was not the case in these data, the researchers said.

Among other explanations, Dr.Chavarro's team suggested that a fat-soluble substance present in dairy products might explain the benefit in high-fat foods. Whole-milk and other high-fat dairy products have higher estrogen concentrations, which decrease circulating IGF-I levels, they said. Alternatively, increased insulin sensitivity among high-fat dairy consumers may have improved ovulatory function.

A limitation of the study, the researchers wrote, is that it did not include a cohort of women known to be planning a pregnancy. Cases were clearly trying to conceive, whereas some pregnancy non-cases may have conceived accidentally. Another limitation was the failure to collect information on exposures of the participants' partners, such as smoking, that might have influenced female fertility.

Given the scarcity of studies in this area, it is important that these findings be confirmed or refuted, the researchers said. It is also important to investigate whether dairy foods have an impact on fertility beyond their association with anovulatory infertility, they added.

In the meantime, Dr. Chavarro advised women wanting to conceive to consider changing low-fat dairy foods for high-fat foods, for instance by swapping skimmed milk for whole milk and eating ice cream. However, he said, they should maintain normal calorie intake and limit their consumption of saturated fats. Once they have become pregnant, they should switch back to consuming low-fat dairy foods.

"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 low-fat milk or equivalent dairy products . . . a strategy that may be deleterious for women planning to become pregnant," Dr. Chavarro and his colleagues concluded.