BAKERSFIELD, Calif. -- A pound here, a pound there. Many adults find their bodyweight starts to creep up as they get older.

Some experts blame increasing hours spent at work and commuting -- which leaves little time for exercise.

But a new study has found family may help make us fat.

Researchers following young women in Australia found those who got married or lived with a partner gained 4 pounds more than those who remained single over a 10-year period.

And having a baby made the problem worse -- women with a child packed on twice as much -- around 9 added pounds.

Overall, partner and baby status had more relationship to women's weight than their physical activity levels.

Researchers are not sure why added family members trigger weight gain. They theorized that single women may try to stay skinny to attract a mate.

In addition, having a baby causes metabolic changes that could increase weight gain - although some experts said the sleep deprivation from having a newborn may cause women to eat more as brain fuel to stay awake.