His mom, dad and sister were all in the army, so it was a natural next step for J. Roundtree. But at his biggest, he weighed about 400 pounds, too heavy to enlist.

Determined to slim down, Roundtree started with workout DVDs, and then moved on to jogging, basketball and swimming.

"Even when I first started doing it people were like why are you doing that?" he told our Columbus, Ohio affiliate WSYX. "For about a month or two I didn't see any results at all.”

But after 18 months of dedication, the 21-year-old literally became half the man he used to be – he now weighs in at 200 pounds!

"I never would have imagined that he would do that but when J. sets his mind to something, don't tell him he can't do it because he'll prove you wrong," said his mother Diane. "When I see him in his military uniform that's going to tear me up, I mean, I will be the happiest mother in the world.”

Roundtree has already enlisted and is set to start basic training in November at Fort Benning in Georgia.

“If I impact somebody with my story then I did my job.”

Every night on Evening Express, we bring you stories about people who are doing good in their communities, around the country and around the world. Click the Facebook and Twitter icons to share this story – and a little inspiration – with your family and friends! Click here to see more Do Good stories featured on the show.