Make sure that you eat lots of nutrient-dense foods such as whole grains, low-fat dairy and brightly colored fruits and vegetables, both for your health and your baby's.

CNN: How can I safely control my pregnancy weight gain?

Fat-free foods don't fit into a nutrient-dense diet unless they're naturally free of fats, like vegetables and fruit.

CNN: Get the biggest bang for your calorie with nutrient-dense food

Researchers don't know why a plant-based diet seems to have a protective effect, but one likely reason is the nutrient profile of vegetarian diets, which tend to be higher in fiber and lower in saturated fat.

WSJ: Vegetarians Live Longer Than Meat-Eaters, Study Finds

Any food with a lot of fat is going to increase the calories and, in essence, make the food less nutrient dense.

CNN: Get the biggest bang for your calorie with nutrient-dense food