"That's the thing about drive-through windows," he says. "You can hide when you order five things, and they ask you if you'd like two drinks with it."
Jessica remembers going on vacation to the Biltmore Estate near Asheville, N.C., where she toured the mansion's sprawling gardens by herself because Mac was too embarrassed to walk around.
"I wanted to be so protective of him because people would just stare," she says. "He saw the world from the seat in the car."
In November 2009, Mac saw the world from a hospital bed when necrotizing fasciitis, a flesh-eating skin bacteria, assaulted the left side of his body.
The infection was dangerously close to his heart, forcing doctors to remove softball-size chunks of infected tissue.
Mac tried to laugh off what was happening but the situation scared him. He didn't want to die.
The low-hanging fruit method
A year later, Mac hit 530 pounds and realized he had to try to lose weight.
"There is not an 'aha' moment," he says. "It was more like, 'OK, if I'm going to try to do this, I'm going to have to do it a little bit at a time. But I better do something before I lose my family to my untimely demise.'"
Mac started "dabbling" at Scrivner's gym. Next he gave up fast food and all-you-can-eat buffets. Then stopped ordering soft drinks. Finally, he started buying healthy food from the grocery store.
Mac describes his strategy as the "low-hanging fruit" method. It allowed him to lose weight without having gastric bypass surgery, hiring a nutritionist or discovering a dieting secret folks in Hollywood would give their big toe to know about.
"It was simple, but it wasn't easy," says Mac. "I knew that I had to make a change because I was sick and tired of not being able to do anything I wanted to do."
Rachel Berman, a registered dietician and director of nutrition for Caloriecount.com, says setting small, attainable goals like the ones Mac made is a better approach to weight loss than using an "all-or-nothing mentality" because people appreciate the progress that comes from each change.
"If you do too much at once, it can be overwhelming and that makes you less likely to maintain it," she says.
Scrivner says he avoided Mac when he first started showing up at the gym, asking members to not say anything to his friend.
"We've hounded him so much over the years," he says. "We were all just kind of holding our breath and hoping he would stick with it."
After Mac lost about 50 pounds, Scrivner approached him about entering an upcoming Jailbreak race.
Together they made a video inviting people to sign up to run the approximately 3-mile obstacle course, promising Mac was going to keep exercising and enter the event, too.
True to his word, Mac competed in the Jailbreak race at 350 pounds.
"I just knew I wanted to complete it," says Mac. "I remember crossing the finish line and being ecstatic."
He has since entered and completed 5K and 10K runs, a half-marathon, a duathlon and a sprint triathlon. He will enter the Hotter 'N Hell Hundred-mile bicycle race this October.
At 230 pounds, Mac is now light enough to ride a motorcycle, an activity his weight kept him from for years. In November he will fulfill a lifelong dream by racing a motorcycle in the Baja 1000 in Baja California, Mexico.
"I had people in my life that I could go to and ask questions and I could use their knowledge," he says. "I did not do this alone."
Mac still does weekly weigh-ins and says the battle to maintain his weight will last the rest of his life. He spends his free time with Jessica and their two children, Matthew, 3 and Libby, 5. The McDonalds will celebrate their 15th wedding anniversary in December.
"I think we're stronger now than we've ever been," says Jessica, who is writing a Ph.D. dissertation about obesity's impact on the learning process. "He's my biggest cheerleader."