The 40-year-old star said his behaviour was unacceptable, reported Us magazine.
"I want to apologise for my inexcusable remarks. My behavior was unbecoming and unacceptable. I've long struggled with my body image and have worked very hard to achieve a healthy weight," he said.
"Instead of responding to comments with compassion, I lashed out in anger," he said and added "I'm not asking for sympathy, but rather understanding and forgiveness. I can say with certainty that I'm taking a deep look at myself and I'm incredibly sorry to everyone I've hurt."
The Twitter bashing reportedly first began when Richman, posted a selfie on Instagram. "Had ordered this suit from a Saville Row tailor over a year ago. Think I'm gonna need to take it in a little," he had wriiten.
A blogger then wrote she 'never liked Adam', which led to a nasty exchange between Richman and several others. The comments have since been deleted.