I don't believe in Starvation Mode (If you've read my book you know why).
However, I do believe in diminishing returns when it comes to weight loss exercises like running or walking.
The amount of calories running or walking causes you to burn (above and beyond your normal resting metabolic rate) is dictated by how much you weigh and how far you move.
If you lose weight then these exercises burn less calories. And, it doesn't matter if this weight is fat OR muscle.
The bottom line - The more weight you lose the less effective these exercises become at burning calories.
You can watch my video for more details: