“I climbed in the mountains,” the 54-year-old former wife of Prince Andrew told L'illustré, the French-language weekly, which features an interview with her in this week's issue.
“I asked the mountains to help me.”
Ferguson, known in England as the Duchess of York, recently joined her former husband and two daughters, Princess Beatrice and Princess Eugenie, for a ski holiday at Verbier in the French-speaking part of Switzerland.
Despite the fact Ferguson and the prince divorced in 1996, they have continued to spend their family ski holidays together for the past 20 years at the upscale Alpine resort, L'illustré notes.
The people from Valais “are so welcoming,” she told the magazine, calling Switzerland her “second country”.
The interview was conducted in English with the responses translated into French.
“J'ai oublié tout mon français,” she is quoted as saying when asked if she has managed to learn a bit of the language during her stays in the region.
Ferguson explained that as a special envoy for the Institute of Global Health Innovation she wanted to raise awareness of the terrible effects of obesity, diabetes and all the illnesses linked to overweight.
As an ambassador “I thought that I should show an example,” she said.
Ferguson said she lost the weight not by going to a fitness club but by exercising in the mountains.
“I can spend four hours doing nothing but climbing, burning calories,” she said, adding that she has also been eating local food, including apples and pears from the region.
Ferguson said she was very attached not just to Verbier but to all of Switzerland.
“I've made it my second country,” she told L'illustré.
“To catch a train in Martigny to go to Zurich and know that it will be on time, it's fantastic,” she told the magazine.
“I like your sense of organization, your discipline.”
Ferguson said she chose to return to Verbier, a place she first visited as a 17-year-old school girl, because the “people of Valais are so welcoming”.
She has teamed up with Christian Sarbach, owner of the Cuckoo's Nest, a mountainside restaurant located at 2,700 metres, to promote Children in Crisis, a foundation she started.
A portion of the prices for certain meals at the high-altitude restaurant, such as the “Fergie” salad, go to the foundation.
“By eating a salad in the restaurant you can educate a child in Afghanistan,” Ferguson told L'iIlustré.