When Mariah Carey and Jessica Simpson each put on 70 pounds while pregnant, chances were good they weren't moving around enough. Even though each reportedly worked out with a personal trainer for 30 minutes or more a day, the rest of the time they must have been pretty sedentary.

A new study shows that's precisely why the pregnancy pounds pack on. If you're pregnant, whether you're at work or at home, make an effort to get up every half hour and walk around (the office, house, yard or parking lot) for at least five minutes.

But don't think that brief bouts of exercise will be all you need for you or your baby. You need to move as much as possible throughout the day (try to walk 10,000 steps), so you don't gain too much weight. Gaining too much puts newborns at risk for diabetes, obesity, depression, autism and premature death for their whole life!

Underweight women should gain 28 to 40 pounds; normal-weight women 25 to 35; overweight women 15 to 25; and obese women 11 to 20.

Other great ways to make sure you don't gain too much weight while you're pregnant: -Don't overeat. You're not eating for two adults! Only increase your calorie intake by around 100 calories a day for the first trimester; 250 for the second; and 350 for the third.

Avoid food cravings by stabilizing hormone levels with five to six small meals, and nine or more servings of fruits and vegetables daily.

© 2013 Michael Roizen, M.D. and Mehmet Oz, M.D.
Distributed by King Features Syndicate, Inc.