"We found that married couples were much more likely to be obese and they were much more likely to watch a lot of television and not engage in enough physical activity, relative to those who were just dating," Gordon-Larsen said.
New studies also show women happen to gain the most weight.
One year after her wedding, Nancy Putorak went to the doctor who suggested that she "must be very happy."
"I thought it to be a strange comment," Putorak said. "But I said, 'Yes I am.'"
Putorak learned she had gained 15 pounds. Thirty-five years later, the pounds had multiplied for her and husband Marty, who was considered clinically obese. Even their dog Zephyr gained weight.
"I think you're content," Nancy Putorak said. "You're not exercising as much because you're busy working on your marriage."
Professor Amy Gorin of the University of Connecticut psychology department says that marriage can work in your favor.
"If one spouse decides to lose weight and make changes in their eating and exercise, it's likely to have a positive influence on the other spouse," Gorin said.
Since her husband started dieting, Putorak has naturally lost weight too, as did Zephyr.
"She does all the cooking in the house, and we ate 95 percent, if not more, of our meals at home," Marty Putorak said. "She used ingredients to keep that calorie and fat content down."
The Putoraks are living proof that the vow -- in sickness and in health -- carries some real weight.
ABC News contributed to this report.