WireImage.com

Gwyneth Paltrow is slimmer thanks to a mostly juice detox diet she followed for three weeks.

"I feel pure and happy and much lighter," the actress writes in her GOOP newsletter. "I dropped the extra pounds that I had gained during a majorly fun and delicious 'relax and enjoy life phase' about a month ago."

Photos: Gwyneth Paltrow

Paltrow goes on: "This program allowed me to work and exercise regularly, something I cannot do if I am on a liquid-only detox."

(Pal Mario Batali once told Us that Paltrow hits the gym three hours a day.)

Related: Gwyneth on her loving the Spanish lifestyle and other celebrity quotes

New York-based cardiologist Dr. Alejandro Junger explains the "Clean" detox works by cutting out most food and "reducing digestive work so detox can occur in full mode. The Clean Program eases digestion by providing two liquid meals a day and a solid one in between, eliminating allergenic and mucus-forming food, which frees up even more energy," the doctor writes.

"I followed [this program] to the letter and I can report that it worked wonders," Paltrow says. "This thing is amazing."

More from US Weekly:

See before and after photos of Us' weight winners.

See more photos of stars working out.

Check out pics of incredible shrinking stars.