"I think the key is you don't have to run a marathon to be active and get a great benefit. Do something fun that you enjoy," he said, adding that some overweight people like to work out in water to reduce some of the strain. "It doesn't have to be pounding or grueling. Start slow and set reasonable goals."
Gneiting said he wasn't sure he'd make it to the finish line Sunday.
"I thought at some point that my joints were going to give out, and there wasn't going to be anything I could do about it," Gneiting said.
He could barely lift his arm to wave to the hundreds of people cheering him on. But seeing one of his sumo friends at the 15-mile mark gave him the boost he needed to plod on.
Gneiting has four sons between the ages of 2 and 7 -- "future sumo champions," he called them -- and a 12-year-old daughter who is also overweight.
"I want her to look at her dad and say, 'I'm not going to let this weight inhibit me.'"
Gneiting said he hopes his marathon effort will serve as a "penicillin shot" for overweight people with low self-esteem.
"I want to show them that just because you're overweight you can still be happy and pleased and proud of yourself and you can still accomplish something."
As for running another marathon, Gneiting said "No way."
"But I said 'no way' last time," he said. "Ask me in three years."