"Alcohol can compete with your affections. It sure did in my case," Bush said. "Affections with your family, or affections for exercise."
"It was the competition that I decided just wasn't worth it," he said.
Minutes after his speech on drugs, the president was back in the Oval Office for meetings with Italy's president.
In a day packed with events, Bush said he still had time for reflection.
"You can reflect when you are exercising," Bush said. "You can reflect, you know, late at night when I am upstairs with the first lady."
But there will be little of that tonight.
The president and first lady are spending the evening hosting one of many holiday parties, which for them means mostly posing for pictures until long after the sun goes down.
With about 13 months left in his presidential tenure, Bush said there are some things he'll miss about being the president.
"I'll miss a lot of the comforts and I'll miss a lot of people," he said.
Bush said he would miss leading the men and women of the military.
"It's such an honor to be the commander in chief of a group of people that are dedicated to the country, selfless, brave," he said.
"I'm going to miss avoiding traffic jams, not being on helicopters, Camp David will be a place we'll miss," Bush said. "On the other hand we'll have memories that will last our life."