Dr Andrew Murrray spoke out as a survey showed 48% said they were likely to enjoy the outdoors over the festive period.
The Edinburgh-based locum GP, who has completed long-distance running challenges around the world, urged the other half of the population to do the same as Scotland prepares for 2013, the Year of Natural Scotland.
Dr Murray said: "Walking is the simplest way to better health and just 30 minutes of walking every day gives more protection against death than any medication.
"More than half of all calories are expended by walking and people underestimate the good that even low levels of physical activity can have, like walking to the shops, or to meetings as I do when I can. Walking can also help fight obesity and is a great treatment for diabetes, high blood pressure, depression and many other conditions.
"Simple physical activity not only makes people feel better quickly, it also adds years of quality life – and a stroll to walk off the excesses of Christmas Day is an ideal step on the path to better health."
Dr Murray completed a 77-day run from John O'Groats to Southern Morocco – the equivalent of 100 marathons, averaging 34 miles a day – in January, arriving in temperatures of 35˚C.
Last month he completed seven ultra marathons on seven continents in just seven days. He travelled to Antarctica, Patagonia, Atlanta, London, Egypt, Dubai and Australia, where he finished on the Harbour Bridge in Sydney, running 31 miles at each location.
Sport Minister Shona Robison said: "In 2013, the Year of Natural Scotland, there will never be a better time to enjoy Scotland's great outdoors."