We are all in agreement, the best way to train to walk is to walk.
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We all know the foods which we can not resist, just try to cut them down. Take a 5kg bag of potatoes on a mile walk to show you how much effort carrying excess weight will be.
just take it steady at first. Don't try to do 6 miles for your first walk. Do 2 miles, 3 days in succession. Like anything manual, get the quality right first, the speed will follow naturally.
Interesting about food. I like cheesecake. If I ate my daily calories in that every day, and nothing much else. I would become sick of it I suspect. It is really down to calories, not what you eat.
Rather than potatoes, get a cheap backpack, some waterproof clothing and a water container. Serves a dual purpose that way.
But leave the 'weight training' till later.