Dr. Gary Steinman of the Long Island Jewish (LIJ) Medical Center in New Hyde Park, NY studied three groups of women:
- Vegans (those who ate no animal products at all)
- Vegetarians (those who didn't eat meat but did consume dairy products)
- Omnivores (those who ate meat, including dairy products)
The results of his study showed that the group of vegan women had twins much less often -- in fact, five times less -- than the other groups.
His theory is that Insulin-like Growth Factor (IGF), a protein that helps embryos survive during the early stages of development, is elevated when cattle are given growth hormone to increase their production of milk and beef. When women ingest the milk from these animals, their own hormones react, stimulating ovulation.
This theory would explain the rapid rise in multiple births in the last thirty years. The increase had often been attributed to advanced maternal age and increased use of fertility technology. However, this study may indicate that dietary habits may also be a factor.
It would also explain why an increase is only evident in fraternal, or dizygotic twinning, which results from the fertilization of multiple eggs. Identical, or monozygotic, twinning rates have remained unchanged. Monozygotic twins occur when a single fertilized egg splits into two. As of yet, no one has clearly identified the causes of monozygotic twinning.