BOSTON -- Two-thirds of Americans are overweight or obese, according to the Centers for Disease Control and Prevention, and the number of people turning to gastric bypass surgery is increasing. But while the surgeries are very successful at taking off the pounds, there can be some unexpected side effects if patients aren't careful.

NewsCenter 5's Liz Brunner reported that Letitia Tucker battled her weight for years. Finally, in 2001, she had gastric bypass surgery. Doctors rerouted her digestive system, making her stomach smaller and bypassing it and parts of her intestine, limiting the amount of food her body could absorb.

"The food just runs through your body so you only absorb somewhere between a quarter and a half of the food that comes into your body," said Dr. Frederick Finelli, of Washington Hospital Center.

With that lack of absorption comes a lack of vitamins, including vitamin A, which is important for good eyesight. Even though Tucker lost more than 200 pounds, she lost a lot more. She lost her sight.

For a while, she continued to drive.

"I was basically following cars because I could see the cars, but I couldn't make out a tag or a red light," she said.

Tucker wasn't taking her vitamin supplements required after surgery, and doctors said that isn't uncommon.

"We try to stress to patients before surgery and after surgery how important it is to take their vitamins, to have follow-up, to show up for their appointments, to get their blood work, but patients are only human," Finelli said.

"When I saw her the first time, she simply couldn't see the eye chart at all," said Dr. Barry Lee.

Tucker could not even see the large E at the top of the chart. Lee put Tucker on vitamin A supplements and her vision was restored.

"After one year, she's back to 20-20 (vision)," Lee said.

Now with her daily dose of vitamin A, Tucker can safely climb behind the wheel.