Just to get back to the original posting about ray mears not being slim...
I have been on many extensive outdoor-stays (living off the land exclusivly) And, I realised, that eating gathered food, made me gain weight. What happens is that at home, I eat an X-amount of food. When I live in the "wilderness" I will eat the same amount of food. The difference however, is that the food I am eating while living wild, is that much richer, and contains more healthy vitamins, etc... in comparison to commercially grown food. Also, in these moderate parts of the world, the forests, are just stuffed with Wild-Foods. I never went hungry! This theory proved true, when at a certain course I went to in the States, most of the people who I stayed in touch with after the course, had the same experience of gaining weight
However, I did find, that it is possible to minimise this difference, when eating Organic