If you are having trouble getting pregnant, and ovulatory infertility is suspected, think of it as temporary health food. OK, maybe that’s going a bit too far. But a fascinating finding from the Nurses’ Health Study is that a daily serving or two of whole milk and foods made from whole milk—full-fat yogurt, cottage cheese, and, yes, even ice cream—seem to offer some protection against ovulatory infertility, while skim and low-fat milk do the opposite.

The results fly in the face of current standard nutrition advice. But they make sense when you consider what skim and low-fat milk do, and don’t, contain. Removing fat from milk radically changes its balance of sex hormones in a way that could tip the scales against ovulation and conception. Proteins added to make skim and low-fat milk look and taste “creamier” push it even farther away.

The depth and detail of the Nurses’ Health Study database allowed us to see which foods had the biggest effects. The most potent fertility food from the dairy case was, by far, whole milk, followed by ice cream. Sherbet and frozen yogurt, followed by low-fat yogurt, topped the list as the biggest contributors to ovulatory infertility. The more low-fat dairy products in a woman’s diet, the more likely she was to have had trouble getting pregnant. The more full-fat dairy products in a woman’s diet, the less likely she was to have had problems getting pregnant.

Our advice on milk and dairy products might be criticized as breaking the rules. The “rules,” though, aren’t based on solid science and may even conflict with the evidence. And for solving the problem of ovulatory infertility, the rules may need tweaking. Think about switching to full-fat milk or dairy products as a temporary nutrition therapy designed to improve your chances of becoming pregnant. If your efforts pay off, or if you stop trying to have a baby, then you may want to rethink dairy—especially whole milk and other full-fat dairy foods—altogether. Over the long haul, eating a lot of these isn’t great for your heart, your blood vessels or the rest of your body.

Before you sit down to a nightly carton of Häagen-Dazs (“The Fertility Diet said I needed ice cream, honey”), keep in mind that it doesn’t take much in the way of full-fat dairy foods to measurably affect fertility. Among the women in the Nurses’ Health Study, having just one serving a day of a full-fat dairy food, particularly milk, decreased the chances of having ovulatory infertility. The impact of ice cream was seen at two half-cup servings a week. If you eat ice cream at that rate, a pint should last about two weeks.