2005

Chestnut, a San Jose State University student, entered the competitive eating scene in 2005 with a break-out performance in the deep-fried asparagus eating championship, in which he beat high-ranked eater Rich LeFevre by eating 6.3 pounds of asparagus in 11.5 minutes. That same year, during Nathan’s Hot Dog Eating Contest, he ate 32 HDB, placing third behind Takeru Kobayashi and Sonya Thomas.

On October 22, 2005, Chestnut set a new world record for downing 32.5 grilled cheese sandwiches in 10 minutes at the Arizona State Fair, as part of the GoldenPalace.net World Grilled Cheese Eating Championship circuit.

2006

Chestnut qualified for the 2006 Nathan’s Contest by eating 50 HDB. As July 4 approached, there was speculation that 2006 might be the year when Kobayashi would be beaten. It was not to be, however. Although Chestnut turned in a great performance, leading Takeru Kobayashi through most of the contest, the final tally put Chestnut at 52 and Kobayashi at ​53 3⁄4 (a new world record). Chestnut lost to Kobayashi in the Johnsonville World Bratwurst Eating Championship in Sheboygan, Wisconsin. He ate 45 bratwurst sausages in 10 minutes. Kobayashi ate 58.

2007

In 2007, Chestnut won the Wing Bowl XV, an annual Philadelphia event at the Wachovia Center. In this competition, he ate 182 chicken wings in 30 minutes, becoming a Wing Bowl champion and record holder.

On July 4, 2007, Chestnut and Kobayashi battled the field in a record-setting hot dog eating battle in Coney Island in Brooklyn, New York, at Nathan’s Hot Dog Eating Contest. Chestnut knocked off Kobayashi 66–63, leading to the latter’s first defeat in the contest in six years.