Got milk? Drinking dairy could give you strong bones, healthy teeth and… twins?

A New York researcher found that women who eat dairy products are five times more likely to have twins than vegan women, who don’t eat any foods made from animals.

Most likely to blame is a protein called insulin-like growth factor, which a cow’s body produces naturally. The protein is the cow’s way of responding to a form of synthetic growth hormone, which many farmers inject into their bovines to increase milk and beef production.

This protein can enhance ovulation, stimulating the ovaries and increasing the chances they will release more than one egg. Researchers say the protein may also act as a shepherd to the embryo, giving it a better chance to survive during the earliest, most critical stages of development.

Like cows, humans naturally produce the protein, but the study shows that vegan women have thirteen percent less insulin-like growth factor in their bodies than milk-drinking women do.

Diet isn’t the only thing that increases a woman’s production of this protein, though. Experts say some women naturally produce more than others. Black women tend to produce more insulin-like growth factor than white or Asian women. Black women also tend to have more twins.

The number of twins born in the United States has been on the rise since 1975. But researchers say the number of twins increased even more in the 1990s when farms began using growth hormone on cows.