The Silence of the Lambs star enlisted the help of his third wife, Colombian-born Stella Arroyave, in 2008 to help him adopt a healthier lifestyle.
The actor admits he became hooked on fatty foods before embarking on an extreme diet, which is believed to be meat-free.
He says, "I was addicted to bread, cookies, whatnot. I love all the bad stuff."
Hopkins now enjoys a simple life revolving around healthy eating and plenty of exercise - although he admits his initial weightloss was so drastic, it surprised even himself.
Images of a frail-looking Hopkins in 2008 and 2009 sparked fears for his health, but he insists he's currently in the best shape of his life.
The star, 73, tells New York Post columnist Cindy Adams, "My wife's no dictator, but she said I must stick to a regimen. So I'm in the gym six days a week, I power walk, live on 800 calories a day. No pasta. No seconds. A sandwich occasionally. Now I'm a health nut.
"I lost too much, 75 pounds in two years. But I gained a little back in Europe (while shooting Woody Allen's You Will Meet a Tall Dark Stranger earlier this year (10))."
His strict new diet means he's no longer able to fit into most of his clothes, so he's donated his larger items to charity.
He says, "I can't get back into my wardrobe. I gave it all away to some mission. I tried tailoring the pants but they look ridiculous."