And he's not making excuses for the .249 batting average or a horrid basestealing percentage or a decline in his defense.
"It was just me," he said. "It wasn't because I signed a [two-year, $10.95 million] contract, it wasn't because of who I was dating [vocal star Rhianna]. I didn't play baseball for the money. I ain't gonna lie and say it's not nice setting yourself up, buying a house for Mom. But it's not the money, it's not the personal life. That had nothing to do with my performance. I can't blame it on anything else."
He said he can only use all that went wrong last year as a learning experience.
"I learned about myself, about dealing with frustration and I was frustrated about 85 percent of the time," he said. "It didn't go the way I wanted personally and for the team. I always feel if I do my part, the team will win, so I was very disappointed.
"Now I know I need to be more vocal, play as hard as I can and stay positive, become more of a leader. Nobody really stepped up last year and became that leader. We need more than Casey Blake and Jamey Carroll. We need all of us stepping up."
Kemp, 26, has been challenged by Colletti and Mattingly to fulfill the potential he showed in 2009, when he won a Gold Glove and hit .297 and drove in 101 runs. Colletti called him out for his defense last April and he was benched in July for, among other things, not hustling.
"That's under the bridge," he said of any lingering issues with Colletti. "We talked, we hugged, we're good. He was frustrated, I was frustrated. Sometimes things happen. Looking back, a lot of things happened last year that shouldn't have happened. But it happened."
Despite the issues that enveloped Kemp last year, he set a personal best with 28 home runs (including in each of the last five games). But his batting average dropped nearly 50 points, he broke his own franchise strikeout record (now 170) and he was caught stealing 15 times in 34 tries.
Kemp said the healthier diet and track training is designed to make him quicker on the bases and in the field.
"I like junk food, but it makes me feel sluggish," he said. "My energy is up. Last year, I wouldn't say I was overweight, but I didn't feel I was running like I should. It was weird. But I've been working out and I feel a lot quicker.
"I want to forget about a season like that," he said. "I don't want to have to talk about a season like that anymore. Turn the page, start a new chapter. I'm excited for the season, I can't wait to get going and get around the guys and have fun."