The study in the American Journal of Preventative Medicine finds young women who got married or lived with a partner gained four pounds over a 10-year period.
Not surprisingly, having a baby packed on twice as much, around nine added pounds.
Overall, partner and baby status had more to do with a women's weight than their physical activity.
Researchers suspect single women try to stay skinny to attract a mate and having a baby may cause metabolic changes leading to weight gain.
