Banks said that when it comes to healthy eating, education is the key.
"The reason that people eat so poorly is because a lot of times it's convenient, it's cheap, and it's what they have always known," she said.
At Pine Ridge, 60 percent of all households receive public assistance, meaning they have an income less than $2,000 a month for a family of four. Each month, eligible households can pick up government-issued commodity boxes, known simply as "commods," to maintain a nutritionally balanced diet.
Some say the "commods" miss the mark, offering only canned meats, cheese, with limited options for fruits and vegetables, and a lot of starchy carbohydrates. Food stamps are preferred by most. Families on the Pine Ridge Indian Reservation are at least six times more likely to be on food stamps than those across the U.S. Residents can drive as much as an hour away to stretch their funds at the handful of supermarkets near the reservation.
An alternative to faraway stores is Pinky's, a convenience store and small Laundromat in the Pine Ridge community of Manderson.
"We are here to ... meet the needs of a community that is far from major shopping areas," said Pinky Iron Plume Clifford, who has run the store for the past 28 years. It is a one-stop shop for top sellers like sodas, as well emergency food items including frozen dinners, milk and eggs.
"If you run out, you have to go to town. There's nothing worse than having a customer come in to buy eggs and you don't have any. Or an item that they need, baby formula, and we don't have it. So you drive the 45 miles to get it," she said.
Clifford recently added fresh fruit and vegetables to her inventory but said the store loses money on the produce, which is pricey to transport.
At Ecoffey's Subway, fresh vegetables are trucked in weekly from Billings, Mont. -- more than 400 miles away. Ecoffey has opened another Subway franchise in nearby Martin, also on the reservation, which receives its fresh supply of produce from Omaha, Neb., 500 miles away.
Despite the high cost of transporting the produce, the restaurants turn a profit thanks in part to the constant business they get from Pine Ridge residents. His customers, Ecoffey said, are getting a good deal.
"For a five-dollar meal," he said, "you can get a whole variety of vegetables that simply people can't afford in a grocery store."
Watch a "20/20" special, "A Hidden America: Children of the Plains" with Diane Sawyer tonight at 10 p.m. ET.