Clare Balding has revealed that being slimmer has given her a new lease of life.

The TV presenter, who was diagnosed with thyroid cancer in 2009, showed off her slimmer self as she graced the front cover of the January issue of Good Housekeeping.

"I downloaded a free app called MyFitnessPal and it tells me how many calories we should be eating if I wanted to lose a certain amount of weight. And then I started walking," said the 42-year-old sports presenter.

"Exercising and calorie counting is very boring but it worked, and it worked quite quickly. I feel much brighter because of it, and I feel capable and I am less tired because I feel fitter."

Clare unveiled the Macmillan Cancer Support Christmas tree, named the Tree of Light, in Covent Garden, London. She dedicated her bauble for the tree to Radio 4's Rory Morrison, who died this year from Waldenstrom's Macroglobulinemia, a form of non-Hodgkin lymphoma. Rory worked alongside Clare's partner Alice Arnold at the station.

"The bauble that I wrote is dedicated to Rory Morrison. He was a great friend of my partner Alice and to her, he was part of her Radio 4 family," she said.

"He died six months ago of a very rare form of blood cancer, so I talked to his widow. He has two young children and this is their first Christmas without him."

Clare, who still has fears about facing another battle with cancer, said the tree has significance for cancer sufferers.

"For those who have had it and have got through it, it's a pretty powerful reminder that we are very lucky," she said.

The Macmillan Tree of Light will be open every day from 11am to 9pm until Christmas Eve in London's Covent Garden.