"I have been eating a lot of pasta and pizza, a lot of carbs," said Phelps, who claimed his third gold medal in three days on Tuesday and his third world record.
He is vying for an historic eight - which would surpass the 36-year-old record of US swimmer Mark Spitz of seven golds at one Games. To get there, Phelps must swim 17 times over the nine days of competition, and get enough rest and calories to keep the campaign alive.
"I have been eating and sleeping as much as I can," said Phelps, who is sharing an apartment with five teammates in the Olympic Village.
"I have woken up about 4:30 to 5am every morning, fallen back asleep for about an extra half-hour and then I have to get up.
"It takes me a while to get up in the mornings, but it is the Olympics," added Phelps, whose prowess is the only reason the swimming schedule has been turned on its traditional head with finals in the morning and heats at night.
US broadcaster NBC lobbied for the switch the better to showcase Phelps in prime viewing time back home.
Phelps has more than proved his assertion that morning finals won't affect him.
But his overall pace is punishing.
"I have been getting as much recovery as I can, it's going to be crucial for the next few days," said Phelps, who had Tuesday evening off but was due for three swims - the 200m butterfly final, 4x200m free relay final and 200m individual medley heats - on Wednesday.
"I have been getting two massages a day and ice baths," Phelps said.
Finding time to rest amid the frenzy is difficult, and made more-so by well-meaning friends from far-flung timezones.
"I had friends texting me all of yesterday after the relay to say they couldn't sleep, because they were so excited, and a few asked how I was napping," he said.
"I texted back: 'I'm not napping, if you keep texting me. I'll talk to you guys after the race tonight.'
"I had to force myself to put it out of my head," he said of the epic relay win. "It's not easy, but I have so much to do in every race. To be able to do that I have to be 100 percent focused and put it out of my head."