I always wonder if it is helpful to think about gaining weight and losing weight. That is, I am not convinced by the idea of 'going on a diet to lose 0.6 stone in a year'.
I would like to suggest that it is better to think about your ongoing lifestyle. That will be a certain balance of eating and exercise. Given that balance, your body will settle down to some weight. If you weigh more than now, then you will gradually lose weight. If you way less that than equilibrium weight, then you will gradually gain weight.
But the point is that you should think long-term about what balance you need to be healthy, and how you can create an lifestyle with enough exercise and reasonable eating habits. If you get that right, then the weight thing will follow.
Instead, thinking about a diet, and a short-term thing to make a short-term change in your weight. Well, it somewhat turns the whole thing into an ordeal to get through, and what happens at the end?
So, what I would take from Colin's mile-a-day calculation is that it is something to think about when working out how you can create a healthy lifestyle for yourself.